Ch . 43: Immune System

1. Ch. 43: Immune System

2. Ch.43: “The Immune System” Organisms must defend themselves from pathogens and from their own damaged cells. There are two main types of defense: Innate Immunity -- present before any exposure to pathogens (from birth): Largely nonspecific Acquired Immunity -- develops as a result of exposure (adaptive): Highly specific

3. INNATE DEFENSE MECHANISMS • Skin: physical barrier, low pH (3-5) • Mucus Membranes: • Physical barrier: wash away pathogens, trap & swallow • Chemical defense:kills bacteria -- acidic pH, • lysozyme (in tears, saliva, mucus) & other proteins

4. White Blood Cells: • PhagocyticWBC’s: engulf & destroy invaders • Neutrophils: 60-70% of WBC’s, attracted to infected tissue to destroy microbes, only live a few days • Monocytes become macrophages: large, long-lived cells, more effective at phagocytosis, 5% of WBC’s, circulate then migrate to tissue, permanently in lymphatic system • Eosinophils (less abundant) target larger parasites – like flukes! • Dendritic cells: can’t ingest microbes but stimulate acquired immunity.

5. Natural Killer Cells: Destroy body cells which are abnormal or are infected with ___viruses_____. • Do NOT use phagocytosis, instead they: attack target cell membrane and lyse it • Antimicrobial Proteins: • Complement proteins: activated by microbes, cause lysing of microbes, more than 30 different proteins, play role in inflammation. • Interferons:secreted by virus-infected cells, it prevents infection of neighboring cells • Defensins: secreted by activated macrophages to destroy microbes

6. The Inflammatory Response: Triggered when body tissue is damaged by a physical injury. • Basophils (WBC’s) and Mast cells (of connective tissue) secrete histamine which initiates the process of: vasodilation and makes local capillaries leakier. • Prostaglandins (from WBC’s and damaged cells): promote blood flow to area (to deliver clotting elements) • Chemokines: attract phagocytes to injured area • Pyrogens (from WBC’s): promote fever (kills pathogen, speeds tissue repair)

7. Process increases number of WBC’s fighting disease and increase temperature (fever): increase rate of phagocytosis If infection or tissue damage is severe, body mounts widespread attack and inflammation: septic shock, common cause of death in critical care units.

8. INVERTEBRATE IMMUNE MECHANISMS: Innate defenses: Sea stars and sponges contain phagocytotic cells: amoeboid cells Insects: exoskeleton acts as skin, hemolymph(equivalent to blood) contains hemocytes Hemocytes act similar to our WBC’s: phagocytose, encapsulate parasites and secrete antimicrobial proteins

9. INVERTEBRATE IMMUNE MECHANISMS: Similar to Acquired defenses:sponges show self versus non-self awareness Worms have shown more rapid response to second exposure to foreignmaterial

10. ACQUIRED DEFENSE (THE IMMUNE SYSTEM) • 4 CHARACTERISTIC FEATURES: • Specificity: acts on particular foreign material • Diversity: able to recognize millions of antigens – any foreign substance which elicits antibody production, usually protein or polysaccharide • Self / Nonself recognition • Memory: acquired immunity prevents 2nd illness

11. Active immunity: antibodies produced in body after infection or vaccination – permanent Passive immunity: antibodies acquired from another animal – breast milk, injection (rabies, snake anti-venom) Temporary (up to a few months) Snakes are milked for their venom. A small amount of the targeted venom is injected into an animal such as a horse. This generates an immune response to the venom, producing antibodies against the venom's active toxin molecules. These antibodies can then be harvested from the horse's blood and used to treat snake bite victims

12. Lymphatic organs: thymus, spleen, lymph nodes, tonsils Lymphocytes: two main classes, both have _antigenreceptors_ and are concentrated in _lymphatic_ tissue. When an epitopeantigen binds, the lymphocytes become activated. Cytokines: proteins that activate lymphocytes.

13. B-cells: made and mature in bone marrow, have two antigen receptors per antibody • Membrane bound antibodies or released antibodies: have variable regions because of gene recombination, recognize 1,000,000 different antigens, but each B cell has ONE specific antigen recognition. • Recognize intact antigens • T-cells: made in bone marrow and mature in thymus

14. T-cells: made in bone marrow and mature in thymus, have one receptor/antibody, 10,000,000 different possible antibodies but each T cell has only ONE specific antigen recognition Recognize fragmentsof antigens

15. Two types of T cells: Cytotoxic T cells: eliminate cancerous cells or infected cells Helper T cells: attaches to cells that have ingested foreign substances, release cytokines to elicit more immune response to infection.

16. The Immune System can mount two different types of responses to antigens: Humoral: antigen recognition or cytokines from helper T results in the production of antibodies by B-lymphocytes called plasma cells (effector cell), also leads to production of more plasma cells and memory B-cells.

17. Cell-mediated: requires the direct activity of T-lymphocytes on foreign cells including -- protozoans, worms, fungi, and transplants Helper T cells: recognize antigen presented by macrophage and bond, also clone more effector cells and memory T cells, release cytokines to increase immune response Cytotoxic T cells: bind infected or abnormal cells and release chemicals to destroy cells.

19. Antigens: Most are proteins or large polysaccharides. Clonal Selection: Antigen bonds to a specific ___lymphocyte___ and triggers cell division to produce millions of ___effector cells___ specific to that antigen. Epitope: portion of the antigen that is recognized by antibodies (can have more than 1 – even millions!)

20. Antibodies: Immunoglobulin proteins (Igs) • Four polypeptides join to form: Y-shaped molecule • Forms a complex with the antigen similar to the enzyme-substrate complex.

21. Five classes: IgM: highly involved in initial response IgG: most abundant in blood, crosses placenta; fetus passive immunity IgA: saliva, tears, breast milk, infant passive immunity IgE: causes mast cells and basophils to release histamines IgD: active in clonal selection in naïve B cells • Causes and neutralization of antigens • Identify and tag invaders to be destroyed by: agglutination lymphocytes

22. Primary Immune Response: Upon exposure, immune response produces: effector cells and memory cells Secondary Immune Response: Memory cells respond faster to re-exposure (permanent immunity)

23. Remember Blood types??? • Most common: O+ • ABO: • A and B represent: antigens on the surface of red blood cells • Type O lacks A and B surface antigens: type O people make antibodies against all others • Rh: • Presence of Rh antigen is represented as: + (positive) • Rh incompatibility occurs when: mom is (-), but dad and baby are (+)

25. Tissue/Organ transplants • Major Histocompatibility complex (MHC): antigen presentation molecules, unique to each person except identical twins, helper T cells respond to these antigens • MHC must be similar enough to allow for transplants: helper T cells will bond if not and cause an immune response to organ or tissue • Individuals who have had an organ transplant must take: immune-depressants to alleviate attack

26. ALLERGIES Evolutionary remnant response to parasitic worms Evolutionary remnant response to parasitic worms Evolutionary remnant response to parasitic worms. • IgE antibody on B cells responds to allergen such as pollen grain, are released and attach to mast cells: • pollen grains attach to antibody and mast cell releases histamine- inflammatory response

27. When many mast cells are activated- widespread histamine release, much dilation of blood vessels leads to decreased blood pressure: • Anaphylactic Shock- remedied by epinephrine

28. Autoimmune Diseases • Immune cells attack own body cells • Examples: Lupus, rheumatoid arthritis, diabetes mellitus, multiple sclerosis

29. Immunodeficiency Diseases • Inability of body to protect against pathogens or cancer • Primary: born with the disease • Example: SCID- severe combined immunodeficiency- B cells and • T cells non-functional

30. Secondary: acquired disease in lifetime; caused by drugs used to fight autoimmune disease, cancers, stress or infection • Example: AIDS (HIV infection) causes a decrease in helper T cells and malfunction of macrophages and brain cells