Defense Against Infectious Diseases

1. Defense Against Infectious Diseases IB Biology

2. Natural Human Defenses • To prevent infection, we employ a variety of defenses to ward off infection: • Physical Defense • Mechanical Defense • Chemical Defense • Biological Defense

3. Physical Defense • Skin • Tough outer layer of dead cells • Contains keratin and very little moisture • Rarely penetrated by microorganisms • Skin Chemicals • Tears (lachrymal glands) for dilution • Sebum (sebaceous glands) w/ fatty acids • Mucus (goblet cells) trap airborne pathogens

4. Mechanical Defense • Nasal hairs filter air passing through nasal passages • Cilia in lungs sweep away microbes trapped in mucus

5. Chemical Defense • Tears, mucus, saliva, and sweat all contain microorganism inhibitors • Lysosyme: enzyme found in many secretions • Catalyzes the hydrolysis of molecules in the cell walls of bacteria • Lactate (in sweat) slows bacterial growth • HCl in gastric juice kills most pathogens

6. Biological Defense • Harmless colonies of symbiotic bacteria live on skin and mucus membranes and inhibit pathogenic microbes • Harmless bacteria also compete with pathogenic bacteria for nutrients • Broad-spectrum antibiotics destroy the good with the bad bacteria, leaving us with fewer natural defenses

7. Immune Response • When a pathogen does sneak by the defenses, the body mounts an immune response • Each pathogen has distinctive protein or glycoprotein markers called antigens which trigger the immune response • Antigen: complex molecules on or produced by pathogens that generate an immune response in host • Self Antigens • Non-Self Antigens

8. Cell Mediated Immunity • White Blood Cells Involved • Lymphocytes: recognize and react with antigens • T-Lymphocytes (for cell-mediated immunity) • B-Lymphocytes (for antibody production) • Macrophages: universal phagocytosis of foreign objects • Also called phagocytic leucocytes

9. Cell Mediated Immunity (Stages) • Macrophages engulf pathogens • Pathogen antigens can become imbedded in macrophage membrane • Specialized T-lymphocytes recognize and fit with antigens • T-lymphocytes go active and replicate rapidly (cloning those T-lymphocytes that recognize the antigens) • Clones differentiate into 4 cell types

10. T-Lymphocyte Cell Types • Cytotoxic T-cells: “killer cells” destroy the antigen (virus or cancer) directly by attaching to them and releasing the chemical perforin • Helper T-cells: direct the attack, summon macrophages, promote T and B cell activity • Memory T-cells: no action, but multiply rapidly if there’s a re-infection • Suppressor T-cells: slow down/stop immune response when job is done

11. Infected Cell with Antigens Or Pathogen Or Macrophage with Antigens Activated or Sensitized T-cell T-lymphocyte (containing binding sites that fit the antigen) Rapid Mitotic Divisions Differentiation Cytotoxic T-Cells Helper T-Cells Memory T-Cells Suppressor T-Cells Destroy pathogenic antigens Coordinate attack by T-cells Used in future infections Slow/Stop immune response

12. Antibody Mediated Immunity • Antibody: glycoprotein (immunoglobulin) • Attaches to specific antigen to destroy it or render it incapacitated until a macrophage arrives • Involved Cell Type: B-Lymphocyte • Stimulated by helper T-cells • Respond to antigens attached to macrophages • 3 Types of B-Lymphocytes • Plasma B-cells: secrete antibodies • Memory B-cells: long-lived, respond rapidly to future infections by the same antigen • Dividing B-cells: produce more B-cells

13. Antibody Mediated Immunity (Stages) • Macrophages engulf pathogen • Pathogen antigens can become imbedded in macrophage membrane • B-lymphocytes activated when they contact antigens • Activated B-cells clone & some convert to plasma B-cells • Plasma B-cells produce and secrete antibodies • Antibodies circulate and attach to antigens and destroy them or form agglutinations (described later)

14. Pathogen or Macrophage with pathogen antigens B-lymphocyte (containing binding sites that fit with pathogenic antigen) Rapid Mitosis (cloning) Differentiation antibodies Memory B-cells Dividing B-cells Plasma B-cells

15. Secondary Response • For cell-mediated and antibody-mediated immunities, the secondary response is faster (second time you get the pathogen) • Memory T-cells and B-cells ensure rapid cloning and differentiation Antibody produced by a plasma B-cell

17. Antibodies and Antigens • The effect of an antibody attaching to an antigen is first a shape change in the antibodies • Next, the antibody may cause agglutination (antigens will stick together) • This can stimulate phagocytosis by neutrophils or macrophages • It can also prevent pathogens from attaching to cell membranes

18. Agglutination

19. Uses of Antibodies • Also called Monoclonal Antibodies • Diagnosis • Detection of HIV with anti-HIV antibodies • Detection of cardiac isoenzyme in suspected heart-attack cases • Detection of HCG for pregnancy test kits

20. Uses of Antibodies (cont.) • Treatment • Targeting of cancer cells with drugs attached to monoclonal antibodies • Emergency treatment of rabies or cancer • Blood and tissue typing for transplant compatibility • Purification of industrially produced interferon • Interferons are glycoproteins used in response to challenges by pathogens. They assist by inhibiting viral replication.

23. Vaccinations/Immunizations • Vaccinations or immunizations generate an immune response, but not to a live pathogen (dead, inactive, or synthetic) • Immune response stimulates memory T and B cells, which remain • Secondary response in the event of an actual pathogen infection is fast and strong • Symptoms not typically noticed

24. Vaccination Pros & Cons • Pros • Dramatically reduces odds of pathogenic infections with symptoms • Potential to wipe out dangerous communicable diseases (smallpox) • Reduces cost of disease treatment • Cons • Possibility of becoming infected (if vaccination contains any live pathogens) • Vaccine cost, access, administration logistics • Overall erosion of immune system? • A variety of other theoretical drawbacks

25. MMR Vaccine • MMR = Measles, Mumps, Rubella • Pros • Measles is a nasty disease, good to vaccinate • Cons • Most boys don’t need Rubella vaccine • Most girls don’t need Mumps vaccine • Girls don’t need Rubella vaccine until sexual maturity • Potentially contributes to autism (hypothesized)

26. Chicken Pox Vaccine • Pros • In adults and some children who haven’t had it before, it can be a dangerous illness • Good for those with compromised immune systems • Saves the discomfort of getting ill • Cons • Its a common illness in children and its usually mild • Re-exposure boost immune response, so vaccination could decrease both • Boosters? Unknown need.

27. Influenza (Flu) Vaccine • Pros • Beneficial for those who get flu every year • Beneficial for those who have dramatic flu symptoms when they get the flu • Beneficial for the very young and the very old and those with weakened immune systems • Cons • Higher (than most vaccines) incidence of contracting a live virus from the vaccine • Enabling immune system to become too relaxed?