Immunity

1. Immunity

2. Body Defenses • First line - barriers • Skin and mucous membranes • Flushing action • Antimicrobial substances • Lysozyme, acids, salts, normal microbiota

3. Second line defenses • Cells – neutrophils, macrophages, natural killer cells • Toll-like receptors on phagocytes recognize carbohydrates on the surface of bacteria • Inflammation • Proteins • Complement • Interferon • Fever

4. All of the previous mechanisms are • NON-SPECIFIC • Third line – immune response • Specific • Memory • Inducibility

5. Antigens - substances recognized as “non-self” These can be: • Infectious agents - bacteria, viruses, fungi or parasites • Noninfectious substances – • Environmental - pollen, foods, bee venoms • Drugs, vaccines, transfusions and transplanted tissues

6. Antigen Antibody Generator The best antigens are: • large • recognized as foreign • complex

7. Two cell types give us the immune response; both are lymphocytes, which are a type of leukocyte, or white blood cell. B lymphocytes or B cells T lymphocytes or T cells

8. The cells of the immune response differ from the cells of the inflammatory response in three ways: 1. They are SPECIFIC and each cell recognizes only one specific antigen. B cells produce antibodies Tc cells attack antigen directly

9. 2. Both produce groups of cells called “memory cells” that act quickly the second time the antigen is encountered. 3. An antigen induces an immune response. Only small amounts of antibodies or T Cells are present before encountering an antigen.

10. Long lasting protection against a specific antigen is immunity. Natural immunity: Not produced by the immune response Species specific

11. Acquired immunity Active – person produces immunity (by producing antibodies or Tc cells) natural artificial Passive – temporary immunity is given (by giving antibodies) natural artificial

12. Lymphocytes Originate : in liver, spleen and bone marrow of fetus in bone marrow after birth From stem cells – hemocytoblasts – that produce all blood cells.

15. To become mature, immunocompetent cells, they must pass through lymphoid tissues in other parts of the body. As they do so, they become committed to becoming either T cells or B cells Cells that migrate through the bone marrow (bursal equivalent) become B cells, and will produce antigens and participate in humoral immunity.

17. Cells that migrate through the thymus glands become T cells and participate in Cell-mediated immunity.

18. Humoral Immunity Humoral immune response : B cells that produce antibodies that travel through the blood. Antibodies are proteins that match the molecular structure of an antigen, and bind to that antigen. This leads to the destruction of the antigen.

19. Antibody

20. When antigen binds to antibody receptors on the surface of the B cell, the B cell divides and differentiates into antibody producing plasma cells and also memory cells.

22. Immunoglobulins • IgG - monomer (crosses placenta) • IgA – dimer – 2 units - in secretions • IgM – pentamer – 5 units • IgD – monomer – on surface of B cells • IgE – monomer – involved in hypersensitivities

25. Cell-mediated immunity • Produced through Tcytoxic or Tc Cells (T8 cell) • DO NOT produce antibodies • Attack invaders directly • May produce toxic chemicals – such as perforins, cytolytic enzymes, etc. • May stimulate cell’s self-destruct mechanism

26. Primary and Secondary Immune Responses Primary response Latent period IgM produced IgG produced later

27. Secondary response • Anamnestic response –much more rapid due to memory cells • Primarily IgG

29. Antigen-Presenting cells (macrophages) place antigen on their cell surface in combination with the MHC II complex Antigen is presented to a specific helper T cell that has receptors that match the antigen – MHC II complex

32. Hypersensitivities “The Immune System Gone Bad”

33. Hypersensitivities • Allergies – Exaggerated immune response against environmental antigens • Autoimmunity – immune response against host’s own cells • Alloimmunity – immune response against beneficial foreign tissues, such as transfusions or transplants

34. These immune processes initiate inflammation and destroy healthy tissue. Four types: Type I – IgE-mediated allergic reactions immediate type hypersensitivity Type II – tissue-specific reactions antibody-dependent cytotoxicity Type III – immune-complex-mediated reactions Type IV - cell-mediated reactions delayed-type hypersensitivity

35. Type I - IgE-mediated allergic reactions or immediate hypersensitivity Characterized by production of IgE Most common allergic reactions Most Type I reactions are against environmental antigens - allergens

36. Selected B cells produce IgE Need repeated exposure to large quantities of allergen to become sensitized IgE binds by Fc end to mast cells after first exposure

37. Second exposure (and subsequent exposures) – antigen binds with Fab portion of antibody on mast cells, and cross-links adjacent antibodies, causing mast cell to release granules. Response is immediate ( 5- 30 minutes)

39. Sometimes beneficial to host – IgE-mediated destruction of parasites, especially parasitic worms.

40. Histamine release: • Increases vascular permeability, causing edema • Causes vasodilation • Constricts bronchial smooth muscle • Stimulates secretion from nasal, bronchial and gastric glands • Also hives (skin), conjunctivitis (eyes) and rhinitis (mucous membranes of nose).

41. Late phase reaction • 2 – 8 hours; lasts for 2 - 3 days • Other mediators that take longer to be released or act: • Chemotactic factors for eosinophils and neutrophils • Leukotrienes • Prostaglandins • Platelet-activating factor • Protein-digesting enzymes

43. Genetic predisposition • Allergy prone or atopic • Can be life threatening, so individuals should be aware • Skin tests – injection – see wheal and flare • Lab tests for circulating IgE

44. Treatment • First wave – antihistamines or epinephrine (blocks mast cell degranulation) • Second wave – corticosteroids and nonsteroidal anti-inflammatory agents that block synthesis of leukotrienes and prostaglandins • Desensitization by repeated injections of allergen – formation of IgG

45. Anaphylaxis – Type I allergic reaction may be localized or general immediate – within a few minutes of exposure Systemic anaphylaxis: pruritus(intense itching) urticaria (hives) Wheezing; dyspnea; swelling of the larynx Give epinephrine

46. Anaphylactic shock • Hypotension, edema (esp. of larynx), rash, tachycardia, pale cool skin, convulsions and cyanosis • Treatment: • Maintain airway • Epinephrine, antihistamines, corticosteroids • Fluids • Oxygen

47. Type II – Tissue specific reactions(antibody-dependent cytotoxicity) • Most tissues have specific antigens in their membranes expressed only by that tissue • Antibodies bind to cells or surface of a solid tissue (glomerular basement membrane)

48. Destruction of tissue occurs: • Destruction by Tc Cells which are not antigen specific- K cells • Complement-mediated lysis • Phagocytosis by macrophages(“frustrated phagocytosis”) • Binding of antibody causes cell to malfunction

50. Type III – Immune-complex-mediated reactions • Caused by antigen-antibody complexes formed in circulation and deposited in vessel walls or other tissues • Not organ specific • Effects caused by activation of complement – chemotaxis of neutrophils • Neutrophils release lysosomal enzymes into tissues (“frustrated phagocytosis”)