Monday, November 2, 2009

 

John Martinko, Department of Microbiology

Room 126  LS II

536-2349

martinko@micro.siu.edu

 

Office Hours: M, W 2-5, or by appointment

 

Web page:

 

http://www.science.siu.edu/microbiology/micr453/

 

Primary resource:

Brock Biology of Microorganisms, 12th edition

 Madigan, Martinko, Dunlap, and Clark, 2009 

 Pearson-Benjamin Cummings, San Francisco, CA

 ISBN 0-132-32460-1

 

Brock Biology of Microorganisms

12 th Edition

Chapter 27:

Microbial Growth Control

 

Sections 27.1-3

 

I. Physical antimicrobial control

 

Heat – autoclave ( F 27.3), Pasteurization, flame (loop)

 

Radiation - gamma rays, microwave, UV

 

Filtration –

 

 II.  Chemical Antimicrobial Control 

 27.4  Chemical Growth Control

Chemical agents are routinely used to control microbial growth.

 

antimicrobial agent: a natural or synthetic chemical that kills

or inhibits the growth of microorganisms.        

 

-cidal agents kill microorganisms

            prefix indicates the kind of organism killed

                        bacteriocidal, fungicidal, and viricidal agents

 

-static agents inhibit microbial growth

                        bacteriostatic, fungistatic, and viristatic agents

 

Some -cidal  agents may also be

-lytic agents -  lyse micoorganisms and viruses

 

Effect of Chemical Antimicrobial Agents on Growth

            Chemicals that have toxicity limit microbial growth in vitro.

 

            Experiment :

            Chemical  antimicrobial agents are added to exponentially

            growing bacterial cultures: Results:  Figure 27.9

 

bacteriostatic, inhibitors of protein synthesis, act by binding to

            ribosomes - tetracycline

 

bacteriocidal, agents bind tightly to cellular targets and are not

            removed by dilution - penicillin

 

bacteriolytic agents induce killing by cell lysis, - a decrease in cell

            number and turbidity - detergents dissolve membranes

            penicillin

 

Measuring Antimicrobial Activity  (Figure 27.10) 
minimum inhibitory concentration (MIC) - the lowest amount of agent needed to completely inhibit the growth of a test organism (tube dilution technique)

 

Figure 27.11

Agar medium is inoculated with the test organism.

 

Known amounts of antimicrobial agent are added

to filter paper disks and placed on the surface of the agar.

 

The agent diffuses from the filter paper into the agar; the further from the filter paper, the lower the concentration of the agent.

 

The diameter of the zone of inhibition is proportional to the amount of antimicrobial agent

added to the disk, the solubility, the diffusion coefficient, and the overall antimicrobial  effectiveness.

 

¥Distinguish between -static, -cidal, and -lytic agents.

¥Describe how the minimum inhibitory concentration of an antibacterial agent is determined 

 

27.5 Chemical Antimicrobial Agents for External Use

1. We must control microorganisms not pathogenic in humans

            Table 27.3 - mostly industrial applications

 

2.We must control growth of human pathogens in vitro

            (on inanimate objects).

            sterilants, disinfectants, sanitizers, and antiseptics.

            Table 27.4 – healthcare, food, water, personal hygiene

 

Table 27.4     Sterilants  are used on inanimate objects

                        (not live tissue)

sterilants, /  sterilizers / sporicides destroy all forms of

            (microbial) life, -even endospores AND viruses

           

Chemical sterilants are used when it is impractical to use heat or

            radiation

Hospital, laboratory applications:

            thermometers, lensed instruments, tubing, catheters,

            reusable medical equipment (respirometers)

 

cold sterilization - enclosed devices that resemble autoclaves

            employ a gaseous chemical agent:

            ethylene oxide, formaldehyde, peroxyacetic acid, or

            hydrogen peroxide

 

Liquid sterilization -sodium (hypo)chlorite solution / amylphenol

            instruments that cannot withstand high temperatures or gas

 

Table 27.4

Disinfectants, Sanitizers

            kill microorganisms, but not all kill endospores,

            used on inanimate objects

 

Disinfectants- kill (almost) all microorganisms - proper mix and

            exposure

Hospital  infection control

-ethanol and cationic detergents

            decontaminate floors, tables, bench tops, walls

Household disinfectants for general disinfection

                        swimming pools, and water purifiers

 

Sanitizers - reduce, but may not eliminate, microbial numbers to

                        a "safe" level- water soluble 

            Food contact sanitizers - mixing and cooking equipment,

                        dishes, and utensils

            non-food contact sanitizers - counters, floors, walls, carpets,

                        air, and laundry

Antiseptics and germicides- chemical agents that kill or inhibit

 growth of microorganisms and are sufficiently nontoxic to be

applied to living tissues.

 

handwashing  (hand  ÒsanitizersÓ/ treating surface wounds

certain antiseptics may also be effective disinfectants (FDA)

 

Antimicrobial Efficacy

Disinfectants and others can be neutralized by organic materials

            e.g., pathogens are often grow in large numbers as

             biofilms, limiting penetration of a chemical agent

 

ONLY  sterilants are effective against bacterial endospores

 

Certain vegetative cells - Mycobacterium tuberculosis-

are resistant to the action of common disinfectants

because of the nature of their cell wall

 

¥Distinguish between sterilizer, a disinfectant, a sanitizer, and an antiseptic.

¥What disinfectants are routinely used for treatment of water? Why are these disinfectants not harmful to humans?

 

Physical / chemical growth control

Sterilizers                 
            Kill all  (even spores) – 37% formaldehyde  
Disinfectants
            Kill all but spores – surfaces
                        3-8% formaldehyde, Lysol, high bleach  Sanitizer
            Kill most – reduce microbial load - not spores -                                   surfaces - low bleach
Antiseptics (germicides)
            Kill most
            Safe for  contact with skin – alcohols
                        reduce microbial load

Selective toxicity
Growth factors / Analogs

III.  Antimicrobial Agents Used in vivo

Treatment and Prevention of Infectious Disease

Compounds for internal use

            Synthetic drugs

            Antibiotics

 

27.6 Synthetic Antimicrobial Drugs

-manufactured chemical compounds that can be used internally

 

selective toxicity - the ability to inhibit or kill pathogenic

microorganisms without adversely affecting the host

First example - proof of concept  Fig 27.15

  

Bacterial structures are different from eukaryotic structures

 -targets for antimicrobial therapy    Fig 27.12

 

Some microorganisms are more susceptible to certain agents

            than others - different structures, etc.

            Fig 27.13      

 

27.6 Synthetic Antimicrobial Drugs

-manufactured chemical compounds that can be used internally

 

selective toxicity - the ability to inhibit or kill pathogenic

microorganisms without adversely affecting the host

First example - proof of concept  Fig 27.15

  

Bacterial structures are different from eukaryotic structures

 -targets for antimicrobial therapy    Fig 27.12

 

Some microorganisms are more susceptible to certain agents

            than others - different structures, etc.

            Fig 27.13

 

27.6 Synthetic Antimicrobial Drugs

-manufactured chemical compounds that can be used internally

 

selective toxicity - the ability to inhibit or kill pathogenic

microorganisms without adversely affecting the host

First example - proof of concept  Fig 27.15

  

Bacterial structures are different from eukaryotic structures

 -targets for antimicrobial therapy    Fig 27.12

 

Some microorganisms are more susceptible to certain agents

            than others - different structures, etc.

            Fig 27.13      

 

Broad spectrum


Narrow spectrum

 

27.6 Synthetic  Antimicrobial Drugs

 

Growth factor analogs

Nucleic acid base analogs

Quinolones

 

Growth factor analogs

-synthetic compounds, structurally similar to a growth factor

 

-subtle structural differences between the analogs and the

  authentic growth factors prevent the analogs from functioning

  in the cell

           

GF analogs for vitamins, amino acids, purines,

              pyrimidines, and other compounds

           

Sulfa Drugs

-first widely used growth factor analogs that specifically

inhibit the growth of bacteria

            -predate antibiotics

            -large-scale screening of chemicals to find a cure

            for streptococcal diseases in experimental animals

 

Figure 27.16 Sulfanilamide

 

p-aminobenzoic acid (PABA) analog - part of the folic acid,

            vitamin - nucleic acids and amino acids

 

Blocks folic acid synthesis, inhibiting nucleic acid synthesis

 

Active only in Bacteria

            Bacteria must synthesize folic acid

                        most animals obtain folic acid from their diet

 

Widespread drug resistance developed with time - 10-20 years

-sulfamethoxazole (a clinically useful sulfa drug) plus trimethoprim,

a related folic acid synthesis competitor, is now used

           

            -drug combination produces sequential blocking of the

                        folic acid synthesis pathway

            -resistance to the combination drug requires two mutations

                         in the same pathway in the same organism

           

Nucleic Acid base analogs/ amino acid analogs

 

Example:  Fig 34.42 

AZT, a nucleoside analog of thymidine

 

Quinolones

 

-another class of synthetic antimicrobial drugs

 

-interact with bacterial DNA gyrase, prevent the gyrase from

            supercoiling bacterial DNA and packaging DNA in the

            bacterial cell

 

DNA gyrase is found in all Bacteria

 -fluoroquinolones (ciprofloxacin) are effective for treating both

 gram-positive and gram-negative bacterial infections

           

            -broad spectrum

 

            - (over)use in beef and poultry

                        prevention and treatment of respiratory diseases

 

Figure 27.18

Ciprofloxacin- urinary tract infections in humans

                        -treat infections from penicillin-resistant strains of

                         Bacillus anthracis (bioterrorism agent)

 

¥What is selective toxicity?

 

¥Distinguish synthetic chemotherapeutic agents from antiseptics and disinfectants.

 

¥Describe the action of a growth factor analog.

 

27.7 Naturally Occurring Antimicrobial Drugs: Antibiotics

            Antibiotics: natural antimicrobial compounds produced

            by fungi and bacteria (other microorganisms) that inhibit or

            kill other microorganisms

 

            -thousands known- <1% are clinically useful

 

-semisynthetic antibiotics

natural antibiotics structurally modified in the laboratory 

?enhanced efficacy?

 

Antibiotics and Selective Antimicrobial Toxicity

 

Figure 27.12

The susceptibility of microorganisms to individual antibiotics and

            other antimicrobial agents varies significantly

 

-gram-positive Bacteria and gram-negative Bacteria may differ in

            their susceptibility to an individual antibiotic

 

-broad-spectrum antibiotics are effective on both groups.

            broad-spectrum antibiotics may find wider medical

              use than a narrow-spectrum antibiotic

              (but vancomycin (MRSA) and isoniazid are very useful)

 

Antibiotics Affecting Protein Synthesis  Figure 27.13
Antibiotics inhibit protein synthesis by interacting with the ribosome - medical and research uses
-streptomycin inhibits protein chain initiation
-tetracycline inhibits protein elongation

Selectivity
-tetracycline is specific for ribosomes of Bacteria       

Problem:
antibiotics that inhibit protein synthesis in Bacteria also      inhibit protein synthesis in mitochondria

-tetracycline is still useful because the eukaryotic mitochondria are not affected at the concentrations used for antimicrobial therapy 

 

-Distinguish antibiotics from growth factor analogs.

 

- What is a broad-spectrum antibiotic?

 

- Identify the potential target sites for antibiotics that

            inhibit protein synthesis and transcription.

 

27.8    Beta-lactam Antibiotics

           

            penicillins, cephalosporins, and cephamycins

 

Figure 27.14 Penicillins and cephalosporins account for 54% of

antibiotics produced and used worldwide.

 

Figure 27.19 Penicillins, cephalosporins, and cephamycins

            -medically important antibiotics, share a structural

            component, the beta-lactam ring

 

Penicillins

-1929 Alexander Fleming characterized an antibacterial product of

the fungus Penicillium chrysogenum as the antibiotic penicillin G

 

-the first clinically effective antibiotic discovered

 

-1939 Howard Florey et al.  - process for large-scale production

 of penicillin

 

Penicillin G is active primarily against gram-positive Bacteria

-Staphylococcus, Streptococcus pneumoniae, S. pyogenes

 

- gram-negative Bacteria are impermeable to the antibiotic

 

Modifications of the penicillin G structure changes properties of

the resulting analogs         F 27.19

 

-semisynthetic penicillins -ampicillin and carbenicillin- are

  effective against some gram-negative Bacteria

 

-modified N-acyl groups of these semisynthetic penicillins allow

 them to be transported across gram-negative outer membranes

 

-resistance: penicillin G is sensitive to beta-lactamase

produced by some penicillin-resistant Bacteria

 

-semisynthetic oxacillin and methicillin are resistant to

            beta-lactamase

 

Mechanism of Action

Beta-lactam antibiotics inhibit cell wall synthesis, therefore are highly selective

 

-transpeptidation reaction cross-links two glycan-linked peptide chains (Figure 6.7a).

-transpeptidase enzymes [penicillin binding proteins (PBPs)] bind beta-lactam antibiotics instead of bacterial glycopeptides

 

Result:

no cross-linking, cell wall continues to be formed, resulting in a weakened, self-degrading cell wall

-osmotic pressure (high inside, low outside) and endogenous autolysins inside the cell, lyse the cell

-bacteriolytic, bacteriocidal

 

¥Draw the structure of the beta-lactam ring and indicate the site of beta-lactamase activity.

 

¥How do the beta-lactam antibiotics function?

 

27.9 Antibiotics from Prokaryotes

 

Macrolide Antibiotics

 

Erythromycin (produced by Streptomyces erythreus) contains

large lactone rings connected to sugar molecules (Figure 27.22)

 

-variations in macrolide ring and sugars = variety of macrolides

 

-protein synthesis inhibitor binds the 50S subunit of the

  ribosome

 

-use- in place of penicillin in patients allergic to penicillin

 or other beta-lactam antibiotics

 

Tetracyclines          Figure 27.23

 

-produced by Streptomyces

-early broad-spectrum antibiotics, inhibiting almost all

            gram-positive and gram-negative Bacteria

 

-naphthacene ring substituted at several positions to form new

tetracycline analogs

e.g. chlortetracycline has a chlorine atom,

oxytetracycline has a hydroxyl (OH) group, no chlorine

 

-natural products

-semisynthetic variations are constantly developed

 

-protein synthesis inhibitor

            interferes with 30S ribosomal subunit function

 

-tetracyclines (and beta-lactam antibiotics) are the most

important groups of antibiotics in clinical use

 

-also used in veterinary medicine

 

-in some countries tetracyclines are used as nutritional

 supplements for poultry and swine

 

-this prophylactic veterinary use is now discouraged

            -fosters drug resistance

 

Fig 27.25 Platensimycin

 

Streptomyces platensis

Inhibits bacterial lipid biosynthesis

 

Broad spectrum

            MRSA,  VRE

 

No toxicity

 

No resistance

 

¥What are the biological sources of tetracyclines? Macrolides?  Platensimycin?

 

¥Compare to the sources of penicillin beta-lactam antibiotics.

 

¥How does each antibiotic lead to death of the affected cell?

 

IV  Control of Viruses

 

27.10  Antiviral Drugs

Viruses use eukaryotic hosts to reproduce and perform

metabolic functions

 

-many drugs that control viruses target host structures and

 are also toxic for the host

 

Strategy

- several agents are more toxic for viruses than for the host

-a few chemical agents specifically target viruses

            HIV

 

Antiviral Chemotherapeutic Agents (Table 27.5).

 

Nucleoside analogs, some of which are

 

nucleoside reverse transcriptase inhibitors (NRTI),

 

all work by the same mechanism:

 

inhibit elongation of the viral nucleic acid polymer (DNA or RNA)

 

Model compound

-azidothymidine (AZT)

 

Fig 34.42  AZT inhibits retroviruses -HIV

 inhibits RNA-dependent DNA polymerase

-analog of thymidine, substitutes 3ÕN3 for the 3ÕOH in deoxyribose, stops chain elongation

 

AZT inhibits multiplication of retroviruses by blocking reverse transcription and production of the virally encoded DNA intermediate

 

Side effects

            -normal cell nucleic acid replication is targeted,

            causing host toxicity (all of the virus inhibitor                 drugs)

 

-NRTIs lose potency with emergence of drug resistance

 

Table 27.5

 

-Nevirapine, a non-nucleoside reverse transcriptase inhibitor

(NNRTI), binds to reverse transcriptase

            -inhibits reverse transcription

 

Phosphonoformic acid - inorganic pyrophosphate analog inhibits

internucleotide linkages, preventing synthesis of viral nucleic acids

 

protease inhibitors (PI) (Figure 27.31) prevent viral replication by

 binding the active site of HIV protease, inhibiting processing of

 viral polypeptides and virus maturation-less toxicity

 

fusion inhibitor -enfuvirtide -a 36-amino acid synthetic peptide

-binds gp41 membrane protein of HIV

-stops the conformational changes necessary for the fusion of

viral and target T lymphocyte cell membranes

 

Influenza Antiviral Agents

 

-adamantane derivatives -  amantadine and rimantadine

  synthetic amines that interfere with an influenza A ion transport

  protein, inhibiting virus uncoating and replication

 

-neuraminidase inhibitors  -  oseltamivir and zanamivir

  block the active site of neuraminidase in influenza A and B

  viruses, inhibiting virus release from infected cells

 

Both categories of drugs are used for treatment and prophylaxis

 of influenza infection (Section 34.9).

 

¥Why are there relatively few effective antiviral chemotherapeutic agents? Why aren't such agents used to treat common viral illnesses such as colds?

 

¥What steps in the viral maturation process are inhibited by nucleoside analogs? By protease inhibitors?

 

27.12 Antimicrobial drug resistance

-the acquired ability of a microorganism to resist the effects

  of a chemotherapeutic agent to which it is normally

  susceptible

 

Origins - antibiotic producers are microorganisms,

-antibiotic-producing microorganisms develop (or have)

             resistance  mechanisms to neutralize or destroy their

             own antibiotics (Streptomyces and Penicillium)

 

-resistance genes may be transferred between and among

  (related) microorganisms by genetic exchange

 

            vertical (chromosomal)

            horizontal (plasmids)

 

Resistance Mechanisms (Table 27.7)

(1) The organism may lack the targeted structure. Mycoplsma

-mycoplasmas, lack bacterial cell wall = resistant to penicillins

 

(2) The organism may be impermeable to the antibiotic

-gram-negative Bacteria are impermeable to penicillin G

 

(3) The organism may alter the antibiotic to an inactive form

-many staphylococci contain beta-lactamase that cleaves the

            beta-lactam ring of many penicillins (Figure 27.27)

Common Modifications  - Figure 27.27

 

 

 

(4) The organism may modify the target of the antibiotic

             (e.g., mutation in ribosome)

 

(5) The organism may develop a resistant biochemical pathway

-Bacteria resistant to sulfonamides modify their metabolism to take

 up preformed folic acid from the environment, avoiding the need

 for the pathway blocked by sulfonamides or the enzyme that

binds PABA acquires a higher affinity for PABA than sulfonamide

 

(6) The organism may be able to pump out an antibiotic entering

 the cell (efflux)

 

Mechanism of Resistance Mediated by R Plasmids

 

Drug-resistant bacteria isolated from patients have R (resistance)

            plasmids

 

-R plasmids encode enzymes that inactivate antimicrobial agents

             (beta-lactamase inactivates penicillin -Figure 27.27)

-R plasmids encode enzymes that prevent drug uptake

            or

-R plasmids encode proteins that actively pump out the drug

                       

-R plasmids may confer multiple antibiotic resistance

            -a single R plasmid may contain several different genes,

            each encoding a different antibiotic-inactivating enzyme

 

Origin of Resistance Plasmids

R plasmids existed before the antibiotic era.

 

-Escherichia coli freeze-dried in 1946 contained a plasmid with

genes conferring resistance to both tetracycline and

streptomycin

-neither antibiotic was used clinically until several years later

 

-strains carrying R plasmid genes for resistance to

Semisynthetic penicillins existed before the semisynthetic

penicillins had been synthesized.

 

-R plasmids with antibiotic resistance genes are found in

nonpathogenic soil Bacteria

 

? selective advantage for major antibiotic-producing organisms

that are  normal soil organisms (Streptomyces) ?

 

Spread of Antimicrobial Drug Resistance

-medical, veterinary, and agricultural antibiotic use provides

selective conditions for the spread of R plasmids and 

confers a selective advantage to bacteria containing R plasmids

 

-Antibiotic resistance is predictable

            -an outcome of ÒnaturalÓ selection

 

-(Over)use of antimicrobial drugs fosters resistance

 

-Increased clinical use of an antibiotic is paralleled by emerging 

            resistance to the same antibiotic

           

            Example: Neisseria gonorrhoeae (gonorrhea) resistance

            to ciprofloxacin (fluoroquinolone) / ceftriaxone

                        Figure 27.28c

 

Overuse

Good news:

Antibiotics are now prescribed at lower levels than in the past

(generally useful in 20% of cases)

-physicians now prescribe about one-third fewer antibiotics for

treatment of childhood infections than they did 10 years ago

 

Bad news:

-ineffective dose, patient non-compliance, lead to sublethal

doses of antibiotics for short periods of time, selecting for

resistant strains

 

Overuse

 More bad news:

 

-Antibiotics used in animal feeds as growth-promoters and 

prophylactic additives may lead to resistance

 

-fluoroquinolones have been extensively used for less than 20 yrs

as growth-promoting and prophylactic agents in agriculture  AND

-fluoroquinolone-resistant Campylobacter jejuni have emerged as

foodborne pathogens. Why?

 

? Routine treatment of poultry flocks with fluoroquinolones to

prevent respiratory diseases?

 

Antibiotic-Resistant Pathogens

 

Almost all pathogens are resistant to some antimicrobial agents

since widespread use of antimicrobial chemotherapy began in the

1950s (Figure 27.29)

 

Penicillin and sulfa drugs are not widely used because many

pathogens have acquired some resistance

 

Some pathogens are resistant to known antimicrobial agents

-vancomycin-resistant Enterococcus faecium (VRE)

-Mycobacterium tuberculosis (XDR TB)

-methicillin-resistant Staphylococcus aureus (MRSA)

-Pseudomonas aeruginosa

-Candida albicans

 

 

Steps to prevent resistance

 

Limited, appropriate use of antibiotics

 

Combination therapy

 

Potential reversal of resistance patterns with restricted use

 

¥Identify the six basic mechanisms of antibiotic resistance among bacteria.

 

¥Identify the primary sources of antibiotic resistance genes.

 

¥What practices encourage the development of antibiotic-resistant pathogens?

 

Brock Biology of Microorganisms

12th Edition

 

Chapter 28:

Microbial Interactions with Humans

II
HARMFUL MICROBIAL INTERACTIONS WITH HUMANS

 

F 28.12

Pathogens are disease-

producing microorganisms

 Various pathogen

 strategies cause disease

 

Virulence

the relative ability of a

pathogen to cause disease

            Growth in the body

            = infection

 

Model pathogens:

Neisseria gonorrhoeae

Streptococcus

Clostridium

Escherichia coli

Salmonella

Influenza

28.6 Entry of the Pathogen into the Host

 

Adherence Table 28.3

Pathogens initiate infections at breaks / wounds in skin /

mucous membranes of the respiratory, digestive, or genitourinary

            tract - specific adherence to epithelial cells (Figure 28.13)

 

Examples:

Tissue specificity

Neisseria gonorrhoeae (gonorrhea)

            adheres to urogenital epithelia through a surface protein

            Opa (opacity associated protein)

            Opa binds CD66 on the surface of human epithelial cells.

 

Species specificity-            

                        H5N1 strain adheres to bird epithelia

                                    not well to humans

 

Polysaccharides, proteins, or protein-carbohydrate mixtures

are synthesized and secreted by the bacteria.

 

slime layer - not attached to the bacteria  (Fig 28.4b)

 

capsule (Figures 28.13 and 28.14) a dense, well-defined

polymer coat surrounding the cell

 

 

Functions:

            1. adherence between other bacteria

            2. protect bacteria from host defense / phagocytosis

 

Vibrio cholerae

No capsule

 

Escherichia coli

Extensive capsule

 

Both adhere to villi  Fig 28.13

 

Fig 28.14 Bacillus anthracis          Extensive capsule

 

Fimbriae and pili

 

 -bacterial cell surface protein structures that function in mobility

  and attachment

 

-Pili of Neisseria gonorrhoeae attach to urogenital epithelium

 

-Fimbriae- strains of Escherichia coli with fimbriae

            (Figure 28.15)

            cause urinary tract infections more frequently than

            strains lacking fimbriae

 

Differences:

 

Type I fimbriae (Escherichia, Klebsiella, Salmonella, Shigella)

-uniformly distributed on the surface of cells

            enterotoxic strains of E. coli express fimbrial proteins

            called CFA (colonization factor antigens)

                        adhere specifically to cells in the small intestine

Fimbriae in E. coli  Fig 28.15

 

 

Pili are generally longer than fimbriae, with fewer pili found on

            the cell surface.

Flagella also increase adherence to host cells and

 boost virulence.

 

Invasion - getting a foothold in the host

-most pathogens must penetrate the epithelium to initiate

            pathogenicity

-attachment is established and invasion occurs at small breaks or

            lesions in the skin or on mucosal surfaces

 

-attachment and invasion can be enhanced on mucosal surfaces

            if normal flora is altered

           

How?  Example:      antimicrobial chemotherapy

                                     illness

 

Type organism:        Streptococcus pneumoniae

 

¥How do Opa proteins on Neisseria gonorrhoeae influence adherence to mucosal tissues?

 

¥What is invasion?

 

¥How does adherence initiate invasion?

 

21.7 Colonization and Growth (Infection)

colonization - pathogen multiplies in wounds, breaks, mucosal

            tissues, even blood

 

Pathogen must find nutrients and suitable conditions

in host (temperature, pH, and presence or absence of oxygen)

-soluble nutrients -sugars, amino acids, organic acids- are limited

-pathogens able to use complex nutrients (glycogen) are favored

 

Iron: concentration influences growth

-transferrin and lactoferrin in animals bind iron tightly

-some pathogens require iron

            -iron salt solution given to an infected animal

            increases the virulence of some pathogens

 

siderophores called aerobactin from Escherichia coli

(encoded on Col V plasmid) removes iron bound to host

transferrin

 

Localized Growth/ Infection and Spread in the Body

 

MRSA

Local infection- boil that may arise from Staphylococcus skin

infections may lead to generalized (systemic) infection

– spread of the pathogen through the blood and lymph systems

            can lead to extensive bacterial growth in tissues

 

Some of the organisms are shed into the bloodstream in large

numbers - bacteremia

 

Widespread systemic infection may occur – septicemia

 

¥Why are colonization and growth necessary for the success of most pathogens?

 

 

¥Identify host factors that limit or accelerate colonization and growth of a microorganism at a local site.

 

21.8 Virulence

 

Virulence is the relative ability of a parasite to cause disease

 

Measuring Virulence

virulence  estimates:

 

LD50 (lethal dose50) = dose of an agent that kills 50% of the

animals in a test group

 

 

Fig 28.16 Virulence quantified

For S. pneumoniae

 -hard to count the few organisms needed for LD50

            highly virulent pathogen - way less than 100 organisms

                        20?

 

LD50 for Salmonella typhimurium, a less virulent pathogen,  

            is much higher than for S. pneumoniae

                        2000?

 

The number of cells of Salmonella typhimurium required to kill

100% is about 10,000 times greater than the number of cells

needed to achieve 100% death with S. pneumoniae.

 

Attenuation- loss of virulence in a pathogen occurs because

            nonvirulent mutants may grow faster in vitro

 

Successive transfers in vitro select such mutants

 

Attenuated strains are used for production of many viral vaccines

            measles, mumps, rubella, some polio vaccines.

 

 BCG (bacille Calmette-Guerin) and Mycobacterium tuberculosis

 

 

 

Toxicity and Invasiveness

Virulence is due to the ability of a pathogen to cause host damage

through toxicity and invasiveness.

 

Toxicity is the ability of an organism to cause disease by means

of a preformed toxin that inhibits host cell function or kills host cells.

 

Major virulence factor for Clostridium tetani is tetanus toxin

-moves to distant parts of the body and initiates

irreversible muscle contraction and often death of the host.

 

Virulence in C. tetani is due almost exclusively to toxicity.

 

Invasiveness

Ability of an organism to grow in host tissue in such large numbers

that the pathogen inhibits host function (causes disease).

 

Major virulence factor for Streptococcus pneumoniae

            = polysaccharide capsule

            - prevents the phagocytosis of pathogenic strains

Encapsulated S. pneumoniae cause extensive host damage

            because they are highly invasive

            -grow in lung tissues in enormous numbers and initiate

            -host inflammatory responses that lead to pneumonia

            (nonencapsulated strains are destroyed by phagocytes)

 

Most pathogens fall between the extreme toxicity of C. tetani

            and the extreme invasiveness of S. pneumoniae

 

Most successful pathogens use a combination of toxins  

and invasiveness

 

            Salmonella, Streptococcus pyogenes, Staphylococcus

 

¥Explain

           

            attenuation

            toxicity

            invasiveness

 

¥Give examples

 

III.        Virulence Factors and Toxins

28.9  Virulence Factors (Table 28.4)

virulence factor

-pathogen-produced extracellular protein that aids in

            the establishment and maintenance of disease

 

Example; streptococci, staphylococci, and certain clostridia

            produce hyaluronidase (enzyme)

-promotes spread of organisms in tissues by breaking down host

            hyaluronic acid (intercellular cement)

            -digestion of the intercellular matrix enables these

            organisms to spread from an initial site

 

Fibrin, Clots, and Virulence

 

Coagulase (E)          produced by pathogenic

                                                Staphylococcus aureus

Coagulase causes fibrin (clot) to be deposited on S. aureus cells

            -protects the coated bacteria from attack by host cells

            -accounts for the extremely localized nature of many

            staphylococcal infections, as in boils and pimples.

            Coagulase-positive Staphylococcus aureus strains are more

            virulent than coagulase-negative strains

 

Streptokinase (E) fibrinolytic substance produced by

            Streptococcus pyogenes

Streptokinase dissolves clots, allowing S. pyogenes to move out

            of wound and into surrounding tissues

 

¥What advantage does the pathogen gain by producing enzymes that digest structural components of host tissues?

 

¥How can the activity of coagulase work to enhance the growth of Staphylococcus aureus?

 

28.10  Exotoxins Table 28.4

 Exotoxins -toxic proteins released extracellularly

Travel from a focus of infection and cause damage at distant sites.

 

4 categories;

1.Cytolytic toxins (CT) - enzymatically attack cells, cause lysis.

 

2.Enzymes (E)- break down host tissues or produce protective

structures for the pathogen

 

3.AB toxins:  AB toxins consist of two covalently bonded subunits

-B subunit binds to a cell surface receptor, allowing the transfer of

 the toxic A subunit across the cell membrane, where it damages

 the cell

 

4.Superantigen toxins (SA)           

stimulates large numbers of immune cells, resulting in extensive

inflammation

 

Fig 28.18 Cytolytic Toxins--hemolysins

 

(a)Streptococcus pyogenes  - streptolysin O

 

(b) Clostridium perfringens- lecithinase

 

Fig 28.19 Staphylococcal alpha toxin - a cytotoxin

 

 

AB toxins

 

Diphtheria Toxin (Figure 28.20)

Corynebacterium  diphtheriae AB toxin is a single polypeptide

-fragment B binds a host cell receptor

             binding induces proteolytic cleavage, separating fragments

            A and B

 

-A enters host cytoplasm - disrupts protein synthesis by

             blocking amino acid transfer from  tRNA to the growing

                        polypeptide chain

 

-A specifically inactivates elongation factor 2 in eukaryotic cells

            (involved in growth of the polypeptide chain) by catalyzing 

            the attachment of adenosine diphosphate (ADP) ribose

            from NAD+ to EF-2,  modifying its ability to bind and transfer

            amino acids from tRNA, stopping protein synthesis

 

Fig 28.20 Action of diphtheria AB toxin

 

Neurotoxic exotoxins

Botulinum toxin:  AB toxin, botulism, Figure 28.21

Most potent biological toxin known 

            1 mg of botulinum toxin can kill > 1 million guinea pigs

            1 g  = 1 BILLION

Botulism

-bioactive toxin complex binds to presynaptic membranes on

the termini of the stimulatory motor neurons at the

neuromuscular junction, blocking release of acetylcholine

 

Fig 28.21  Botulinum-poisoned (blocked) muscle cannot

receive excitatory A signal - contraction is prevented

Result: flaccid paralysis (death by suffocation)

 

Botulinum toxin-poisoned (blocked) muscle cannot receive an

            excitatory signal

 

Contraction is prevented

            transmission of the nerve impulse to the muscle through

            acetylcholine - muscle receptor binding/excitation

             is blocked

 

Result: flaccid paralysis and death by suffocation

 

Tetanus toxin AB toxin  Figure 28.22

a.         Normally, interneurons release glycine, an inhibitory

neurotransmitter.

 

G binds to receptors on the motor neurons,

stopping release of A by motor neurons and inhibiting muscle

contraction, allowing relaxation.

 

b.  Tetanus AB  toxin moves through motor neurons to the

spinal cord and binds specifically to ganglioside lipids at the

termini of the inhibitory interneurons.

 

TT blocks G release: motor neurons are not inhibited, leading

to continual release of A and uncontrolled contraction of the

poisoned muscles.

 

Uncontrolled contraction results in spastic paralysis

            trismus/lockjaw

 

 

Fig 28.22  Tetanus -spastic, twitching paralysis

            -affected muscles are constantly contracted

 

Fig 35.21 Tetanus.

Muscles of the mouth- trismus or lockjaw

Respiratory muscles-death due to asphyxiation.

 

¥Identify features are shared by all exotoxins.

 

¥Identify the unique features of exotoxins.

 

¥Are bacterial growth AND infection in the host necessary for the production of toxins? Explain your answer.

 

28.11  Enterotoxins

 

 

 

Enterotoxins are exotoxins whose activity affects the

small intestine

 

-causes massive secretion of fluid into the intestinal lumen

 

-leads to vomiting and diarrhea

 

 

Figure 28.23 Cholera toxin action of  cholera toxin

AB enterotoxin produced by Vibrio cholerae (cholera)

            one A subunit : five B subunits

-B subunit binds specifically with the ganglioside GM1 (a complex

            glycolipid) in the cytoplasmic membrane of epithelial cells

-the A subunit crosses the cell membrane, activates adenyl

            cyclase, converts ATP -> cAMP

-higher cAMP levels cause secretion of chloride and bicarbonate

            ions from mucosal cells into the intestinal lumen (out)

            - secretion of large amounts of water into the lumen (out)

            - rate of water loss into the small intestine can be greater

                        than the reabsorption of water by the large intestine

            - massive net fluid loss occurs - vomiting, diarrhea

 

Victims generally die from dehydration/ electrolyte imbalance

 

Treatment - oral fluid replacement with solutions containing

            electrolytes and other solutes

 

 

Other enterotoxins

 

Some enterotoxigenic Escherichia and Salmonella toxins are

functionally and structurally, related to cholera toxin

 -produced in the gut by colonizing bacteria

 

 -Staphylococcus aureus enterotoxin is a superantigen

            -stimulate large numbers of immune lymphocytes

            -causes systemic and intestinal inflammatory responses

 

Shiga toxins are protein synthesis inhibiting AB toxins 

 Shigella dysenteriae

 E. coli O157:H7 (Shiga-like toxin)

 

Foodborne diseases

 

Food poisoning - acquired by the ingestion of preformed toxin

            -growth in host is unnecessary

            Staph enterotoxin, botulism (latency - hours)

 

 

Food infections - require active growth to form toxins

            V. cholerae,  E.coli, Salmonella

            Food infections require  bacterial growth in the host,

            followed by toxin production (latency - days)

 

¥What key features are shared by all enterotoxins?

 

¥Describe the action of Vibrio cholerae toxin on the small intestine. Why does this lead to massive fluid loss?

 

ORT – Oral rehyderation therapy 

ORS- oral rehydration solution

UNICEF /WHO contents of reduced osmolarity ORS packets 2006.

A 1-liter preparation of ORT solution contains:

sodium chloride (NaCl) - 2.6g

trisodium citrate dehydrate - 2.9g

potassium chloride (KCl) - 1.5g

anhydrous glucose - 13.5g

recommendation for zinc supplementation

 

Sports drinks are formulated to rehydrate healthy individuals

 -too much sugar and too little electrolytes for ORT

 

 

28.12 Endotoxins

 

Endotoxin: the lipopolysaccharide (LPS) produced by

            gram-negative Bacteria as part of the outer layer of

            cell envelope is toxic

 

LPS endotoxins are cell-bound and released in large

            amounts only when cells lyse

            -in contrast, exotoxins are secreted products of living cells

            (Table 28.5).

 

Endotoxins have been studied primarily in Escherichia, Shigella,

            and especially Salmonella (gram- Bacteria)

 

Endotoxin Structure and Function

LPS consists of three covalently linked subunits (Figure 4.23)

            lipid A, a core polysaccharide, and the O-polysaccharide.    

 

 Fever - universal symptom

            endotoxin stimulates host cells to release endogenous

            pyrogens (cytokines) that affect temperature control in the    brain

 

Other symptoms

-diarrhea

-rapid decrease in lymphocyte, leukocyte, and platelet numbers

-release of cytokines leading to general inflammation

 

Large doses:

            death from hemorrhagic shock and tissue necrosis

 

Toxicity of endotoxins is MUCH lower than that of exotoxins (mice)

 

LD50 for endotoxin is 200-400 mg per animal

 

LD50 for botulinum toxin is about 25 pg

 

            about 10,000 fold less!

 

¥Why do gram-positive Bacteria not produce endotoxins?

 

 

¥Why are drug preparations tested for endotoxin?

            (Parenteral administration)

 

Start here 11/5

IV. Host Factors in Infection

 

 Uncontrollable risk factors: age, genetic makeup,

            tissue specificity

 

Controllable risk factors: diet, stress

 

Host Risk Factors for Infection

 

Age, Stress, and Diet

            Age -not controllable-        

            Infectious diseases are more common in the very

            young (<1 yr) and in the very old ( > 50, 65)

 

Infant diarrhea

            pathogens have a greater opportunity to become

            established and produce disease

            (limited by establishment of local flora? Immunity?)

 

            diarrhea from pathogenic strains of Escherichia coli is more

                        frequent in infants <1 year.

 

Infant botulism

            intestinal infection with Clostridium botulinum - infants <1 yr

 

            C. botulinum colonizes and grows, secretes botulinum toxin,

                        leading to flaccid paralysis

            contracted by ingestion of C. botulinum from soil, air,

                        (raw honey)

            prevented by establishment of the (competitive) intestinal

                        normal flora in older children and adults

 

> 50, 65 years

            infectious diseases are much more common

            much more susceptible to respiratory infections,

                        particularly influenza          

                        ?declining immune response to pathogens?

 

Stress (controllable)

fatigue, exertion, poor diet, dehydration, or drastic climate

            changes are stressors

                        -increase the incidence and severity of infections

 

Experimental Salmonella infections:

Rats subjected to Salmonella challenge after intense physical

  activity (long periods) show a higher morbidity and mortality

  than rested animals

 

Hormone studies 

- stress hormone cortisone produced at higher level under stress

                        Activates "fight or flee" response

                        anti-inflammatory agent

                        - suppresses inflammation, inhibits activation of

                         immune response, promotes infection

 

Diet (controllable)

 

Vibrio cholerae numbers necessary to produce cholera in an

            exposed individual are drastically reduced if the

            individual is malnourished

 

Dietary restriction of sucrose and good oral hygiene

  eliminate tooth decay.

 

Without dietary sucrose, Streptococcus mutans and

S. sobrinus are unable to synthesize the polysaccharide

slime layer necessary for adherence to tooth surfaces.

 

The Compromised Host   

Hosts in which one or more resistance mechanisms are inactive

            -probability of infection is therefore increased.

Healthcare-associated infections

            morbidity -2 million cases  / year

            mortality -100,000 deaths / year

Hospital procedures - catheterization, injection, surgery etc.,

            may introduce microorganisms

Organ transplant patients are treated with immunosuppressive

            drugs that reduce patient resistance to infection

General stress of illness

 

Compromised hosts outside the hospital result from:

            smoking, excess consumption of alcohol, i.v. drug use,

            lack of sleep, poor nutrition, acute or chronic infection with

            another agent

 

Chronic infection example:  HIV infection

HIV-AIDS deaths are generally due to opportunistic pathogens,

microorganisms that do not ordinarily cause disease in an

uncompromised host

 

Genetic diseases that attack the immune system predispose

individuals to infections - die from infection.  Which organisms?

¥Identify factors that control susceptibility to infection and cannot be controlled by the host.

 

 

¥Identify factors that control susceptibility to infection and can be controlled by the host.

 

28.14 Innate Resistance to Infection

 

Natural Host Resistance

 

Examples of species differences

 

Rabies

Raccoons and skunks are very susceptible to rabies infection.

Opossums rarely acquire rabies.

 

Anthrax (Bacillus anthracis)                     

            -birds are totally resistant to anthrax

            -fatal blood poisoning in cattle

            - cutaneous anthrax - mild pustules in humans          

            -pulmonary, or airborne, anthrax (bioterrorism) is

                         >90% fatal in humans

 

HIV infection occurs only in higher-order primates

            (great apes and humans)

Why?

            CXCR4 protein on T cells and

            CCR5 protein on macrophages

              are uniquely expressed in primates

 

They act as cell surface receptors and specifically interact with

            HIV gp120 protein

 

Other animals lack these receptors, cannot bind HIV,

and are thus protected from HIV infection

 

 

Figure 28.25 Physical and Chemical Defenses of the Body

Skin - effective barrier to the penetration of microorganisms.

            Sebaceous glands in the skin secrete fatty acids and lactic

            acid, lowering to pH 5

            -inhibits colonization of many pathogenic bacteria

             (blood and internal organs are about pH 7.4)

Ciliated epithelial cells on nasopharynx and trachea move cells into

            oral secretions

            -expectorated or swallowed and killed in the stomach

            -continual movement also prevents adherence

Stomach acidity (pH 2) kills/ reduces numbers of ingested bacteria

Resident microflora and pH prevent colonization

            stomach (pH 2)

            small intestine (pH 5) and

            large intestine (pH 6–7) (bacterial numbers of 1010 or more

                        per gram of contents)

Lysozyme found in  lumen of the kidney and the surface of the eye

 

 

Tissue Specificity (Table 28.6) Pathogens must be able to

            adhere and colonize at the site of exposure

 

Adherence to an exposure site does not guarantee colonization:

           

The site must meet nutritional and metabolic requirements of the

            Pathogen

 

Pathogens cause disease at tissue-specific sites:

 

 

Clostridium tetani cells or endospores introduced into a deep

            wound promotes growth and tetanus toxin production

            in the anoxic zones created by local tissue death

C.tetani pathogen is killed by the acidity of the stomach

           

 

Enteric bacteria - Salmonella and Shigella

            -colonize the intestinal tract, cause food infections

            -do not cause wound infections

 

- Identify physical and chemical barriers to pathogens.

            How might these barriers be compromised?

 

- How might preexisting infection compromise an

            otherwise healthy host?

 

 

Friday, November 20, 2009

 

Chapter 29 Essentials of Immunology

Chapter 30 Immunity in Host Defense and Disease

 

Readings:

Chapter  29.  Introduction

Sections 29.1. 29.2, 29.3, 29.4

30.2, 30.3, 29.9, 29.11, 30.4, 30.5,

30.7, 30.8.

 

Topic order:

1.The system: cells and organs

 

2.  Immunity: non-antigen specific and antigen specific

Innate                                          Adaptive

 

3.  Outcomes – artificial and natural

 

Lecture 1 Objectives:  Identify the cells and organs involved in

the immune response

 

Overview of immunity:

            innate/non-specific immunity

            adaptive/specific immunity

 

*inflammation: host response (induced by specific or

non-specific immunity)

            characterized by heat, pain, swelling, redness

 

 

*immunity:  the ability of a host to resist infection

 

Immunity often results from/in inflammation

 

*innate (non-specific) immunity:  the general ability of a host to

            resist most pathogens

 

*adaptive (specific) immunity:  the ability of a host to recognize

            and interact with an individual pathogen or pathogen

            component (individual molecular recognition)

           

Innate immunity often triggers adaptive  immunity.

The result is host resistance to individual pathogens.

 

*antigens: molecules (proteins, polysaccharides, lipids,

            nucleic acids) recognized by the adaptive immune

             response

*immunogens: molecules which elicit a specific immune

            response

29.1  Cells and Organs of the Immune Response

 

 

Blood: cellular and non-cellular elements

           

            non-cellular liquid portion:  

           

            proteins, salts in solution = plasma

           

            plasma with clotting proteins removed = serum

 

Table 29.1

 

Immune cells are nucleated white blood cells (wbc, leukocytes): 4.5-11 x 106 /cc

            Lymphocytes: 1.0-4.8 x 106 /cc ~ 20%

            Myeloid cells            

                        granulocytes: 3.5-6.2 x 106 /cc ~ 70%

                        monocytes: up to 8.0 x 105 /cc ~ 10%

 

Location and Origin of Leukocytes

 

Myeloid lines - granulocytes and monocytes

Lymphoid lines - lymphocytes

 

Circulate through the blood vascular system as well as the

lymphatic system

 

 

Fig. 29.1 Origins of immune cells

 

Blood vascular system

Lymph circulatory system 

Fig 29.3

 

Primary lymphoid organs-

thymus (T cell maturation)

bone marrow (B cell maturation)

 

Secondary lymphoid organs contain B and T lymphocytes and

APC (phagocytes)

 

-lymph nodes – lymphatic system

-MALT - all mucosal tissue, especially gut (GALT),

lungs (BALT)

-spleen – blood

 

Extravasation cells pass between the blood circulatory system and the lymphatic system. Leukocytes, but not rbcs, travel to all regions of

the body and travel back and forth between the two circulatory

systems.

 

Section 29.2 Innate immunity

The players are the phagocytes involved in INFLAMMATION

 

1.Macrophage- found in tissues  - myeloid –not circulating F 29.3

 

2. Neutrophils (PMNs) Fig 29.4a (myeloid precursor)

            Circulating effector cell-

            -moves to DANGER along chemokine/cytokine gradients

            (sources- macrophages, injured cells, mast cells, etc.)

            -extravasation

 

Fig 29.5 Overview of immunity

 

Phagocytes (and many other cells) express PRRs

-pattern recognition receptors that act as

pathogen-restricted activators of phagocytosis

   Macrophages make up 20% of some tissues

 

PRRs interact with PAMPs- pathogen associated

 molecular patterns

 

Phagocyte PRR interacts

with  pathogen PAMP

 

Leads to phagocytosis

 

Activates phagocyte

 

Fig 30.1 Pathogens, PAMPs, and PRRs

 

PRR-PAMP  examples:

MBL -mannose-binding lectin  -soluble –in blood

-  binds to PAMP- mannose on pathogen cell walls

 

TLR-4 - Toll-like receptor-4 - a membrane-bound

  receptor on phagocytes

Intreracts with

 bacterial lipopolysaccharide – a PAMP on

  Gram- bacteria: Escherichia coli, Neisseria gonorrhoeae

 

TLR-2  - a membrane-bound receptoron phagocytes

  binds peptidoglycans -a PAMP on

(Gram+ bacteria: Staphylococcus, Streptococcus

Function of Phagocytes

PMNs, monocytes and macrophages: kill bacteria

            directly

phagolysosome - an intracellular vacuole containing anti-bacterial substances and the ingested organisms

 

Phagocytes are activated by chemokines, cytokines and PRM

interaction to produce toxic oxygen compounds

 

H2O2 (hydrogen peroxide)              1O2 (singlet oxygen)

O2- (superoxide anion)                   NO (nitrous oxide)

OH. (hydroxide radical)

HOCl (hypochlorous acid) 

 

These compounds are toxic to most pathogens.  Synthesis

requires increased uptake and metabolism of O2 

            respiratory burst  - Fig 29.6

 

Fig 29.7

Neisseria gonorrhoeae in neutrophils

 

Leishmania in a macrophage

 

29.3 Inflammation, fever, and shock

 Inflammation

            Erythema (redness)

            Edema (swelling)

            Pain

            Fever (heat)

What sets up inflammation?

 

1.Injury such as  infection of host cells

 

3.Injured host cells release soluble chemotactic

            mediators-chemokines

 

3.Chemokines activate nearby macrophages and draw in PMNs

 

4.         Phagocytes ingest and kill pathogens

 

Phagocytosis causes:

            Destruction of pathogen, activation of phagocyte transcription,

                        resulting in

           

5.  Production of soluble, secreted mediators - cytokines

 

6.  Cytokines (proinflammatory IL-1, IL-6, and TNF-alpha) cause

            inflammation and may also recruit and activate more

             effector cells, including some involved in adaptive immunity.

 

Local vs.Systemic inflammation

 

1.Local inflammation results in rapid mobilization of effectors

            to the site of injury, leading to localized, targeted destruction

             of the affected tissue and pathogens.

 

2.         Widespread release of cytokines, for example in the

            bloodstream results in widespread release of cytokines, and

            whole-body inflammation:  Septic shock (sepsis) and death.

 

Summary for INNATE IMMUNITY

Mediated by interactions between pathogens and       phagocytes

Molecular interactions involve PRRs-
            pathogen recognition receptors –
                        (Toll-like receptors-TLRs)
 
                                                and

PAMPs – pathogen-associated molecular patterns

 PRR-PAMP interactions activate phagocytes
            O2 - dependent killing

 

29.4 ADAPTIVE  IMMUNITY
ANTIGEN-SPECIFIC IMMUNITY

Mediated by interactions between lymphocytes and   phagocytes (with digested pathogens)

Lymphocytes act directly or activate other effector systems to neutralize pathogens

BUT

the target is shifted: 
 
individual pathogen-specific molecules - antigens

 NOT general shared pathogen features (PAMPs)

 

Lymphocytes- lymphoid precursors- reside in secondary

 lymphiod organs- spleen, lymph nodes, MALT  (Fig  29.1)

 

T lymphocytes

            T cells- have antigen-specific receptors

            called TCRs-T cell receptors

 

 

 

B lymphocytes

            B cells have antigen-specific receptors called

            immunoglobulins

            antibodies

 

Fig 29.8  Three features of adaptive immunity

 

SPECIFICITY

-Immunity identifies and destroys a single target (pathogen)

 

MEMORY

            -vaccination

            -titer

 

Tolerance

            -no autoimmunity
            -transplants

 

Fig  29.21

Memory

 

Titer  Fig 32.10

 

Titer:  Amount of immune response (antibody).

 

Optimal 2-4 weeks after antigen

exposure.

 

Rise in titer is circumstantial evidence for infection.

 

Acute and convalescent serum.

 

 REVISIT Fig 29.5

 

Section 30.2 Adaptive immunity and T cells

 

T cells receive antigen from APCs

-Macrophages and dendritic cells in the secondary

 lymphoid organs 

 

APCs present antigen

(pieces of the pathogen about 10-20 amino acids in length)

 

Antigen is embedded in MHC

 

MHC I - all cells

 

MHC II – APCs only

 

Fig  30.2

Adaptive immunity is mediated by

T lymphocytes interacting  with

MHC-antigen on APC phagocytes.

 

APCs

-Macrophages

-Dendritic cells

 

Cell-mediated responses.

 

T cell subsets Tc, Th ( Th1 and Th2)

 

T cytotoxic  (Tc) cells interact with peptide-MHC on any

infected cells.  Tc cells then kill the infected target cell via

perforin and granzymes

             viruses, tumors

            Example: Varicella zoster - chickenpox

 

T helper (Th) cells interact with peptide-MHC II on APCs

Th1 cells produce cytokines  -soluble proteins-  that activate other effector  cells

            - the phagocytes, particularly macrophages.

            intracellular pathogens

            Example:  Mycobacterium tuberculosis

 

Th2 cells interact with B cells -next

 

 

Sec 30.3, Fig 30.3.

Antibody production requires a Th2  cell and a B cell. The B

cell is the APC. 

 

(1)Antibody  (antigen receptor) captures antigen (pathogen).

 

(2)B cell-processed antigen is presented  to the T cell,

which makes cytokines that

 

(3) Stimulate the B cell - makes antibody and differentiates to 

-plasma cell; antibody producer

-lots of memory cells

 

REVISIT FIG 29.5

 

 Section 29.9

F 29.15

Immunoglobulin G

 

V - variable region

-unique structure and function 

-binds one ag

 

C - constant region

-conserved structure and functions

-cell binding

-complement binding

 

150,000 MW

2H (50K), 2L (25K)

 

C domains identify Ig class

 

IgA - secretions - dimer

 

IgD- ? B cell surface

 

IgE- bind mast cell

            cause allergy,

            parasite immunity

 

IgG- serum

            secondary antibody

            binds complement

 

IgM- serum - pentamer

            primary antibody

            binds complement

 

29.11 Complement

Complement is series of proteins that interacts sequentially  

with pathogen-targeting molecules of the innate and adaptive

immune response.  Complement deposition results in:

-opsonization - enhanced phagocytosis

-lysis  pathogen or infected cell

 

Complement and antibodies interact in the sequence shown

in Fig 29.22

 

Section 29.11Figure 29.22  Complement is a series of interacting proteins that activate phagocytes or lyse targets. 

1. Ag-Ab complex on cell fixes complement, targets cell for phagocytes (opsonization) or
2. Lyses cell

 

Review:

1.Identify the end cells in the myeloid lineage.  What is their function?

 

2.Identify the primary and secondary lymphoid organs.  What are their functions?

 

3.What are PAMPs and PRRs?

 

4.Define the four major symptoms of inflammation.

 

5.Identify the APCs.

 

6.Identify the role of each T cell in adaptive immunity.

 

7.Identify the role of B cells, antibodies, and complement in adaptive immunity.

 

Chapter 30

            Natural immunity

           

            Artificial immunity / immunization

           

            Immune response diseases

                        allergy, autoimmunity

            Superantigens

 

II. Immunity and the Prevention of Infectious Disease

 

Innate immunity - no phagocytosis - recurrent bacterial, viral, and fungal infections

 

30.4 Natural Immunity

 Natural active immunity - adaptive immunity acquired by exposure to a pathogen (infection), followed by an adaptive immune response (T cells and Ig)

 

Natural passive immunity

 

Passive immunity - the transfer of preformed antibodies or

immune T cells from one animal to another by natural means.

 

Examples:

Cross-placental maternal antibodies in fetus / newborn - IgG.

Breast milk – IgA

 

Contrast active and passive immunity - Table 30.1

 

30.5 Artificial immunity and immunization

 

Vaccination / immunization

 

Antiserum (serum containing antibodies) or

            gamma globulin (purified antibodies) injected into an

            animal transfers immunity.

                        -artificial passive immunity

 

            Example:  hepatitis 

 

Purposeful exposure to a controlled dose of harmless antigen

to induce active immunity - antibodies or T cells

                        -artificial active immunity

 

 How do we make vaccines?

 

Immunization- strategies and examples

Antigen or antigen mixture: vaccine

 

 Inactivated antigens: toxoid (denatured toxin)

            reduced biological effects, but retained antigenicity

            tetanus toxoid

            diphtheria toxoid

 

Dead (inactivated) cells/ virus

            influenza (i.m.)

 

Attenuated cells / virus

            influenza (live attenuated influenza vaccine)

            MMR

 

Fig 30.4 Immunization recommendations 

 

Infants/ children

 

Adults

 

Middle age

 

Elderly

 

Compromised

 

Latest information:

 

http://www.cdc.gov/vaccines/default.htm

 

Immunization benefits

 

Direct benefits for the immunized individual - no disease

 

Indirect benefits

-Control infectious disease in the population - herd immunity

 

-Unimmunized individuals may be protected because

            immunized individuals cannot acquire or spread

            infection

 

Successes:  MMR  Fig 34.15

Smallpox- eradicated by 1980 - immunization and follow up

Polio – controlled

 

Review

 

Provide an example of natural passive immunity.

What are the benefits?

 

 

Provide an example of artificial active immunity.

What are the benefits?

 

III. Immune Response Diseases

 

Hypersensitivity: inappropriate immune response that results

in host damage

 

30.7 Allergy, Hypersensitivity, and Autoimmunity

 

 Categorized in Table 30.3 by immune effector mechanism

 

Table 30.4, Fig 30.5            Type I

Immediate hypersensitivity mechanism 

IgE, mast cells, cross-linking, activation, degranulation,

release of vasoactive mediators, symptoms

 

Fig 30.6         Type IV mechanism 

Th1 activation of other effectors - macrophages, Tc

Poison ivy, Tuberculin/ Tuberculosis

 

Table 30.5    

Type II - Antibodies to cell-surface antigens  - cytotoxic

Antigen is often organ-specific (diabetes, myasthenia gravis, GoodpastureÕs)

 

Type III - Antibodies bind to soluble or circulating antigens form immune complexes, fix complement, damage tissue (SLE, RA)

 

Why doesnÕt everyone get autoimmune diseases?

Age - increased chances with time

 

 

Gender - SLE, RA

 

 

 

Heredity  - Diabetes mellitus - MHC

 

 

 

?Antigen exposure and cross-reaction??

 

Review

 

Type I

 

Type II

 

Type III

 

Type IV

 

30.8 Superantigens

 

Act directly on host cells, (over)activate the immune system, cause host damage.

 

Streptococci and Staphylococci, in particular, produce exotoxin proteins.  These proteins bind MHC-TCR proteins outside th eusual peptide-bindinf g sitre.

 

Superantigens interact with T cells from multiple clones, stimulating larger numbers of T cells  (?10,000 times as many?) than a normal response.

 

Result:  Release of cytokines leads to massive inflammation

 

Examples (Table 28.4) Fig 30.7

 

Staphylococcal enterotoxin - diarrhea

 

Erythrogenic toxin (Streptococcus pyogenes) – scarlet fever

 

Toxic shock syndrome toxin – TSST – toxic shock

Like septic shock, massive systemic inflammation

Staphylococcus

 

Review

 

Define the differences between normal and superantigen activation of T cells.

            Antigen?

            Numbers of cells?

 

Identify the binding site (molecules) for superantigens on T cells and APCs

 

SUMMARY - IMMUNITY

Innate immunity

Phagocytes provide non-specific immunity to a variety of pathogens and pathogen products.  Innate immunity is triggered by interactions of PAMPs with PRRs.

 

Remember-

Cytokines/ chemokines interact with their respective receptors, activating phagocytes and triggering inflammation.

Adaptive immunity

APC phagocytes present pathogen components (antigens) to another subset of nucleated blood cells, the T lymphocytes.

T cells, found in lymph nodes, MALT, or the spleen, bear antigen-specific receptors (TCRs) on their surface.  

T cells can activate other T cells to produce antigen-reactive effector T cells or can interact with B cells that produce antibodies. 

Activated T cells and /or antibodies are capable of neutralizing or destroying antigens. 

The adaptive immune response is characterized by specificity, memory, and tolerance.

 

Final outcome of both innate and adaptive immunity:

      Inflammation

 

Result:

Protective immunity:

Active and passive immunity

      Natural and artificial (immunization)

 

Pathogen damage and (sometimes)

      Tissue damage –hypersensitivities, superantigens