ABNORMAL IMMUNE FUNCTION (2).pptx FOR POST RN

rythrocyte Disorders (2).pptx FOR [PST RN

1. ABNORMAL IMMUNE FUNCTION BY SAIQA PERVEEN HEALTH EDUCATOR

2. ALLERGY & HYPERSENSITIVITY It is inappropriate, powerful immune response to an antigen (allergen) that is harmful to the host. First contact of individual with antigen sensitizes i.e., induces the antibody & subsequent contact elicits allergic response. Type I, II & III involve antigen- antibody reactions & type IV is cell-mediated. 4 types according to parts of immune system involved. Type I, Anaphylactic Hypersensitivity: Usually called “allergy” & passed genetically. Antigen involved is free & foreign. Antigen induces formation of large quantities of IgE antibodies which bind firmly to mast cells & basophils. Re-exposure with the same antigen results in cross-linking of antigen to IgE , it causes degranulation of mast cells or basophils releasing histamine, protease, slow reacting substance of anaphylaxis, eosinophil chemotactic substance, neutrophil chemotactic substance, heparin & platelet activating factors, within minutes leading to immediate hypersensitivity reaction. These substances cause dilation of local blood vessels, attraction of eosinophils & neutrophils to reactive site, increased permeability of capillaries & contraction of local smooth muscles.

3. Some allergic reactions are: Anaphylaxis: when a specific allergen is injected directly into circulation , it can react with basophils of blood & mast cells immediately outside blood vessels if they have been sensitized by attachment of IgE . A wide spread allergic reaction occurs throughout vascular system & closely associated tissues called “anaphylaxis”. Histamine in blood causes body wide vasodilation, increased permeability of capillaries with plasma loss from circulation. Death may occur due to circulatory shock within a few minutes, unless treated with epinephrine to oppose histamine effects. Leukotrienes called slow reacting substance of anaphylaxis released from activated basophils & mast cells cause spasm of smooth muscles of bronchioles , eliciting an asthma like attack sometimes causing death by suffocation.

4. Urticaria: result from antigen entering specific skin areas causing localized anaphylactoid reactions. Histamine released locally causes vasodilation that induces red flare. Local swellings of skin called “hives”. Hay Fever/ Allergic Rhinitis: Allergen reacts with antibody in nose. Histamine released cause local intranasal vascular dilation & increased capillary permeability. Fluid leaks rapidly into nasal cavity, nasal lining becomes swollen & secretory. Antihistamine drugs can give relief. Asthma: Allergen- IgE reaction occurs in bronchioles of lungs. Slow reacting substance of anaphylaxis cause spasm of bronchiolar smooth muscle causing difficulty in breathing. Antihistamine drugs have less effect b/z histamine does not appear to be major factor eliciting asthmatic reaction.

5. Type II, Antibody- mediated/ Cytotoxic Hypersensitivity: Antigen is fixed & intrinsic to tissue in which reaction occurs. Antibodies involved are IgG & IgM moving freely in blood. When an antibody reacts with an antigen on a cell surface, complement system becomes activated causing lysis of cell & attract phagocytes to the site. E.g., hemolytic disease of newborn & transfusion reactions. If antibodies are mistakenly directed against self antigens, it leads to destruction of body’s own tissues called autoimmune disease.

6. Type III, Immune complex-mediated hypersensitivity: Antigens can be self or exogenous & free. Antibodies are IgG or IgM & they are also free. Antigen-antibody react with each other & form immune complexes which circulate in general circulation. Normally they are removed by reticuloendothelial system. In persistent microbial or viral infection, they persist & get deposited in various tissues e.g., kidneys, joints(arthritis) & blood vessels. When immune complexes are deposited, they activate complement system, neutrophils are attracted to site & inflammation & tissue injury occur. In kidneys they block glomerular capillaries, impairing kidney function & causing glomerulonephritis. E.g., penicillin allergy (antibodies bind it).

7. Type IV, delayed type(cell- mediated hypersensitivity It is due to an over-reaction of T cells to an antigen. When an antigen is detected by memory T cells, it provokes clonal expansion of T cells & large no of cytotoxic T cells are released to eliminate antigen. Usually this system is controlled, but if not actively aggressive cytotoxic T cells trigger chronic inflammation which damages normal tissues. E.g., contact dermatitis( nickel allergy), graft rejection, poison ivy toxin in skin, air born antigen can cause lung edema & asthmatic attack.

8. Autoimmune diseases: 1. Rheumatic fever: Body becomes immunized against tissues in joints & heart especially heart valves after exposure to specific type of streptococcal toxin that is similar to body’s self antigen. 2. Glomerulonephritis: Person becomes immunized against basement membrane of glomeruli. 3. Myasthenia gravis: immunity develops against acetylcholine receptor proteins of neuromuscular junction, causing paralysis. 4. Lupus erythematosus: Person becomes immunized against many different body tissues at the same time, a disease that causes extensive damage & often rapid death.