Introduction to Lab Ex. 24: Hypersensitivity

Response to antigens (allergens) leading to damage Require sensitizing dose(s) Introduction to Lab Ex. 24: Hypersensitivity Hypersensitivity is thus an exaggerated response of the immune system. There are 4 types of hypersensitivity reactions: - Type 1: IgE mediated Anaphylaxis reactions - Type 2: Cytotoxic reactions (IgG/IgM) - Type 3: Immune complex reactions (IgG) - Type 4: T D cell mediated reactions Types 1, 2, 3 are antibody mediated and are of the Immediate type Type 4 is cell (T D )mediated and is of the Delayed type

Involve IgE antibodies, mast cells, basophils Localized: Hives or asthma from contact or inhaled antigens Systemic: Shock from ingested or injected antigens Type I (Anaphylactic) Reactions Figure 19.1a

On first exposure (sensitizing) to allergen IgE antibodies are formed. IgE antibodies circulate through the body and bind by their Fc portions to receptors on the surface of mast cells and basophils. On reexposure to the same antigen, binding of the antigen to IgE on the surface of mast cells and basophils could lead to crossbridging Crossbridging stimulates the degranulation of the mast cells.

Mast cells: - found in connective tissue of the skin, respiratory tract and in surrounding blood vessels - contain granules with chemicals (mediators) - have many receptors for Fc portion of IgE - cross bridging causes degranulation Basophils: - circulate in blood stream - contain granules with chemicals (mediators) Mediators include: - histamine - leukotrienes - prostaglandins

Histamine effects: - increase permeability of capillaries - cause swelling and redness - increase mucous secretion - cause smooth muscle contraction Leukotrienes effects: - cause prolonged smooth muscle contraction (spasms of the bronchial tubes) Prostaglandin effects: - cause mucous secretion - cause smooth muscle contraction (respiratory system) Results of allergic reaction: inflammation (neutrophils, eosinophils) - distension of capillaries, swelling, mucus secretion, smooth muscle contractions

Skin testing RAST – to identify allergens Type I (Anaphylactic) Reactions Figure 19.3

Treatment/ therapy: - Antihistamine: block histamine binding sites in nose and skin - Desensitization: stimulate IgG production to allergen (allergy shots) - Cromolyn sodium: stabilizes mast cell membranes, thus inhibiting histamine release in nasal tissues/bronchial mucus membranes - Epinephrine: relaxes smooth muscles in lung; constricts blood vessels (raises blood pressure); immediate action