Immunology

Transcript Immunology

Immunology and Microbiology

Host-Microbe Interactions Non-specific (Innate) Immunity

• • First line of defense (Non-specific resistance) Physical and Chemical Defenses Normal Flora • • • • Second line of defense (Non-specific resistance) Phagocytosis Inflammation Fever Antimicrobial substances: Complement, Interferon • • Third line of defense (Specific Resistance) Antibodies B cells and T cells

• Detect enemy • • • • • Immobilize/kill enemy Send out alarm Recruit help Make environment unpalatable for enemy/prevent spread (process repeats) • • • Toll-like receptors on macrophages; complement (3 ways) Phagocytosis; lysis Cytokine release • Inflammation; fever

Toll-like receptors: What are some evolutionarily conserved features of microbes that our immune cells could recognize?

Step 2.

Steps in phagocytosis

http://www.cellsalive.com/mac.htm

Clinical and laboratory features of patients with an inherited deficiency of neutrophil membrane complement receptor type 3 (CR3) and the related membrane antigens LFA-1 and p150,95. Ross GD.

• Over the last 3 years a group of more than 20 patients has been described worldwide who have a similar history of recurrent bacterial infections and an inherited deficiency of three related leukocyte membrane surface antigens known as CR3, LFA-1 and p150,95 (function unknown). It is believed that the patients with this disease have a reduced or absent expression of all three antigen family members on different WBC types. Neutrophils have a reduced phagocytic response to bacteria and yeast as well as a reduced ability to migrate into sites of infection.

Adapted from J Clin Immunol. 1986 Mar;6(2):107-13.

The Complement System

• • • Activated in 3 ways – Antibody-antigen (augments specific defense) – Molecules that recognize bacterial sugar polymer (mannan) – “Random binding” to cell surfaces (C3b) Triggers a cascade 3 effects

Effects of complement system 1. Opsonization

2. Membrane Attack Complex (Lysis)

Are G+ or G-ve cells more susceptible to killing by MAC? Why?

Bacterial cell wall structure

Gram-negative and gram-positive bacteria http://www.blackwellpublishing.com/trun/artw ork/Animations/Overview/overview.html

3. Inflammation

• • • What else triggers inflammation? Tissue damage What are features of inflammation?

What is the inflammatory process?

Which of the following statements about inflammation is false?

A. Vasodilation results in leakage of blood components B. The process can cause damage to host tissue

C. It is always accompanied by a fever

D. The signs of inflammation are redness, swelling, heat and pain E. It can be triggered by activating toll-like receptors (macrophages produce cytokines)

INFLAMMATORY PROCESS

trauma or infection chemotaxis and diapedesis vasodilation

Is inflammation a good thing?

Is that pus?

The movement of phagocytes in the direction of an infection, due to attraction by complement, chemicals released by microorganisms, and the remnants of damaged cell membranes is a process called

phagocytosis.

B) chemotaxis.

diapedesis.

cyto adherence.

FEVER

• • • • • Hypothalamus controls body temp Pyrogens resets temp set point Pyrogens: cytokines; LPS Unfavourable for bacterial replication Favourable for immune response--phagocytosis; lymphocyte replication etc

Interferon and viral infections: a protective alerting system

Complement and immunoglobulins can coat the outer surface of a microorganism, enhancing phagocytosis. This process is called

chemotaxis.

fixation.

C) opsonization.

endotoxicity.

membrane attack complexing.

Host-Microbe Interactions 1. Innate (Non-specific) Defenses a. Chemical and Physical; ( Biological ) b. Normal Flora

Host-Microbe Interactions

1. Contact with microbe a. colonization (normal flora) b. defense breached c. Loss 2. Infection a. cure, immunity b. establishment c. carrier 3. Disease d. Allergy

All of the following statements are true with regard innate immunity EXCEPT:

These responses are not directed specifically to the infectious agent.

These responses are not affected by prior exposure to the agent.

These responses are inborn.

These responses are operating constantly to prevent the establishment of any infection.

E) All of the above are true with regard to innate immunity.

First line of defense Barriers Physical Chemical

An enzyme found in our tears, saliva, serum, and mucus that degrades the peptidoglycan of the cell wall of Gram positive bacteria is called A) amylase

lysozyme.

keratinase.

streptokinase.

peptidase.

First line of defense Chemical & Physical Barriers

Which of the following substances is produced by the cells in our body and interferes with the multiplication of viruses by stimulating the production of antiviral proteins?

antivirase.

interferon.

inhibitase.

complement.

multiplicase.

Which of the following are mechanisms that protect the respiratory system from infection? 1. mucus 2. mucociliary escalator 3. normal flora 4. lysozyme 5. acidic environment

1,2,5.

1,3.

1,2,3.

2,4.

E) 1,2,3,4.

Normal Flora of Humans

What normal flora?

• • • •

A normal human has approximately 10 13 body cells and 10 14 individual normal flora!

microbes that grow on external and internal surfaces of the body without producing obvious harmful effects Transient microbial flora : only occasionally inhabit the body.

Symbiotic relationships: Commensal, Mutualistic, Parasitic

Body sites that harbor normal flora

Importance of the normal flora

• • • • • Prevent attachment of invading organisms Produce antimicrobial substances against other microbes that are pathogens Stimulate immune system – Cause the production of cross-reacting antibodies Significant nutritional source of vitamins

Cause dental caries and gum disease

How do we acquire microflora?

• • • • During birth & within first 12 hours after delivery Breast-fed v bottle-fed Contact with people, environment, food.

Eruption of teeth & introduction of solid food.

What leads to changes in the normal flora?

• • • • Antibiotic treatment Immunosuppression Diet Changes in physiology , e.g. estrogen-glycogen effect

Normal Skin Flora

• • • • 1000 to >1 million/ cm 2 Diphtheroids: G+ rods & cocci, e.g. Corynebacterium & Proprionobacterium , e.g. P.acnes (acne) facultatively anaerobic, coagulase negative Staphylococci [carriers of coagulase positive S. aureus in population] Yeasts

First line of defense (Non-specific resistance) • Physical and Chemical Defenses • Normal Flora Second line of defense (Non-specific resistance) • Phagocytosis • Inflammation • Fever • Antimicrobial substances: Complement, Interferon Third line of defense (Specific Resistance) • B cells and T cells • Antibodies and Humoral Response • Cellular Mediated Immunity

Genetic Immunodeficiencies

Common Variable Hypogammaglobulinemia: Affecting both males and females and occurring at any age, this disease is manifest by repeated pyrogenic infections. The B cells fail to mature to plasma cells. Passive Ig is the common treatment. Chronic Candidiasis: Fungal infection by nonpathogenic yeast is the manifestation of a number of afflictions where few mature T cells are present. These patients often have B cells that respond to T-independent antigens, but

Candida albicans

(yeast) stimulates a poor antibody response. 1) 2) What immune component fails to be made in CVH?

How come a defect in T cells affects antibody response in chronic candidiasis?

The two arms of the adaptive immune system

Antigen: a molecule (or parts of one) that causes antibody generation

(Immunoglobulin)

The specific region on an antigen recognized by an antibody

Antibody Structure Diversity in antibodies due to variable region An infinitely large number of possible immunoglobulins; 5 different classes: IgG, IgM, IgA, IgD & IgE Made by V(D)J recombination http://en.wikipedia.org/wiki/V%28D%29J_reco mbination

Effects of Antigen-Antibody Interactions

Fig. 16.06

Effects of Antigen-Antibody Interactions-2 Parasites; virally – infected host cells NK cells release perforins and proteases (16.8)

How is the antibody response triggered?

1. T-cell dependent antigens 2. T-cell independent Ags e.g. polysaccharides, LPS

response of young children to these antigens is poor Result: Clonal selection and expansion of B-cells

Result:

Memory

A plasma cell

Why is the RER in plasma cells so extensive?

Clonal Expansion

Negative selection Affinity maturation Class switching: IgM – IgG—IgG / IgA Formation of memory cells

Memory Cells mediate secondary response and lifelong immunity

Fig. 16.11

Cellular Immunity

• Cytotoxic T cells (CD8+) Eliminates cells infected with virus, intracellular parasite • Helper T cells (CD4+) Mediates B-cell proliferation; macrophage activation Both stimulated by dendritic cells (cells of innate immunity) Both produce cytokines that stimulate own proliferation

T cells activated by dendritic cells

B C A

A. Recognition of virally-infected cell by cytotoxic T cell results in apoptosis

B: Helper T-cell activation and interaction with B-cells

C. Helper T- cells can also activate macrophages

Fig. 16.19

Activated macrophage: a hungry beast!

•enlarged •membrane becomes irregular •increased number of _lysosomes, containing antimicrobial substances________ •produce nitric oxide

Applications of Principles of Immunity

IgG levels in fetus vs infant

What is passive and what is active?

Principles of Immunization

• • • • • Natural or artificial Passive or active Natural passive , e.g. IgG across the placenta Artificial passive, use of immune serum globulin e.g. IgG fraction of donor blood.

Active involves lymphocytes and confers lasting protection due to memory 56

Can you put the types of vaccines listed into categories?

Vaccines

• • • • • Induce artificial active immunity Preparation of living or inactivated microbe or virus or their components.

Adjuvants help to induce better response Effective vaccines should be safe, few side effects, lasting protection, low cost, stable, easy to administer Should induce appropriate specific response 59

Attenuated immunizing vaccines

• • • • • • Use modified live microbe/virus Induce infection & mild disease and solid long lasting immunity.

Single dose can induce immunity Potential for spread to other people helps to develop HERD IMMUNITY Disadvantages: may cause disease, cannot use in pregnancy, require refrigeration Examples: measles, mumps, rubella, Sabin polio vaccine, (Vaccinia ( for smallpox)) 60

Inactivated Immunization

• • • Inactivated by chemical treatment but still antigenic Cannot cause infection Disadvantages: require several boosters, may cause side effects • Whole agent--Use inactivated bacteria or virus – Examples : Salk polio vaccine, diphtheria & tetanus toxoids 61

Inactivated Immunization: Subunit vaccines

• Use isolated antigens or antigen fragments: a subunit of the total agent – bacterial toxin (toxoid), protein subunit, polysaccharide – e.g vaccines against meningococci, pneumococci, pertussis, H. influenza – Recombinant vaccine, e.g. Hepatitis B. Require several doses. 62

Future developments & information

• • • • HIV/AIDS, Malaria, cancer Use of DNA alone Further information: www.immunizationinfo.org

vaccine.chop.edu (Children’s Hospital of Philadelphia) Developing New Smallpox Vaccines, in EID, vol7, #6, 2001. On line at www.cdc.gov/eid 65

Serology

• Testing for the presence of a specific antigen using specific antibody (antiserum) • Examples: ELISA blood test for HIV, home pregnancy test http://www.sumanasinc.com/webcontent/anim ations/content/ELISA.html

Mechanisms of Pathogenicity Attachment and Colonization Avoidance of Immune System Toxin Production

• Washwater containing Pseudomonas was sterilized and used to wash cardiac catheters. Three patients undergoing cardiac catherization developed fever, chills, and hypotension. The water and catheters were sterile. Why did the patients show these reactions?

Host-Parasite Dynamics

Reservoirs Modes of transmission Adherence and invasion of host Growth in/on host Evade host defense Damage host Leave host for reservoir or new host

How do bacterial pathogens overcome host defenses?

VIRULENCE FACTORS bacterial products or structural components that contribute to pathogenicity or disease A.

promote bacterial colonization of the host (infectivity and invasiveness) obtain nutrients, especially iron evade immune system actively harm the host (toxins)

A1. Adherence Factors: Attachment and Colonization 1. Motility Swim through mucus and towards epithelial cells of mucus membranes (chemotaxis) Most microbes that colonize bladder, intestines are motile (need to reach epithelial cells before flushed out) Non-motile Vibrio cholerae mutants are less virulent

2. Pili and fimbrae with adhesins

Pili allow uropathogenic bacteria to resist flushing and colonize the urethra.

Once bacteria attach, some remain on cell surface like E. coli and biofilm bacteria.

Others INVADE host cells.

2a. Capsule Polysaccharide coat is sticky and aids attachment

Also protects cell from inflammatory response



Reduced complement fixation and phagocytosis.

3b. Biofilm: community of encapsulated bacteria Aid attachment of other bacteria; evade host immune system

A2. Invasion Proteins that induce phagocytosis in non-phagocytic cells Bacterium escapes from vacuole and lives in cytoplasm Advantage of living in host cell: Ready supply of nutrients Protected environment

Mechanism of Invasion: Type III secretion system Pore formed through bacterial membrane and wall and human cell membrane.

Deliver proteins directly from bacterial cytoplasm to human cell cytoplasm that polymerize actin filaments.

Invasion of tissues possible too.

Invasion virulence factors that damage tissue or dissolve materials e.g. Collagenase breaks down connective tissue Clostridium perfringens: gangrene

C. Virulence Factors that help evade immune system.

i. Avoid or escape phagocytosis

• • • destroy phagocytes or signals for recruitment capsule type III secretion of proteins that directly inhibit phagocytosis: Yersinia pestis

• prevent opsonization (Protein A and Fc receptor)

ii) evade specific immune response (antibodies) Antigenic variability (phase variation): alter genes that encode surface proteins like adhesins Low immunogenicity: ‘Teflon’ pathogens (spirochaetes) few surface proteins IgA protease

Viral evasion of cytotoxic T cell and NK cell attack

D. TOXINS: Virulence factors that damage the host.

Endotoxin is only released upon death (lysis) of bacterium

What causes lysis?

LPS, especially when in the blood, can cause a number of pathophysiological changes such as: a. fever production b. inflammation c. tissue destruction d. respiratory distress e. capillary damage (leading to petechial rash, capillary leakage, and hypovolemia f. intravascular coagulation g. hypotension h. decreased cardiac output i. Septic shock j. wasting of the body k. diarrhea (from endotoxin in intestines)

Exotoxins Released from viable bacteria Gram-negative and gram-positive cells Most potent toxic substances known 1 ng of botulinum toxin kills 1000 people Bind to specific receptors on host cells (more localized effect than endotoxin) Effect depends on cell type the toxin binds •Neurotoxins (nervous tissue) •Cytotoxins (general tissue) •Enterotoxins (GI tract)

Examples of bacterial exotoxins Botulinum toxin (neurotoxin) Blocks release of neurotransmitter Paralysis results Cholera toxin (enterotoxin) Fluid loss results

Genetics of Pathogenicity can involve many genes, complex.

chromosomal, plasmids, bacteriophage Transfer of virulence genes via transformation, transduction, and conjugation.

Virulence factor genes often transferred as groups called pathogenicity islands: type III secretion system