Hypersensitivity Reactions PDF

HYPERSENSITIVIT 9 Y hypersensitiv ity Exaggerated response to a typically harmless antigen that results in injury to the tissues, disease or even death. Gell and Coombs devised a system for classifying hypersensitivity reactions into hour types based on immunologic mechanism...

HYPERSENSITIVIT 9 Y hypersensitiv ity Exaggerated response to a typically harmless antigen that results in injury to the tissues, disease or even death. Gell and Coombs devised a system for classifying hypersensitivity reactions into hour types based on immunologic mechanism involved antibody and the nature of triggering antigen. mediated Type I, II & iii cell mediated Type iv Type i hypersensitivity Commonly thought of as allergies The antigens that trigger type 1 hypersensitivities are called Distinguishing feature: SHORT allergens TIME lag phase Key immunologic components: IgE Basophils Mast cells Eosinophils Clinical manifestation: Wheal-and-flare skin reactions Rhinitis Allergic asthma Anaphylaxis type 1 hypersensitivity reaction immune IgE mediator synonym anaphylactic Timing Immediate Antigen Heterologous Complement NO involvement Release of mediators Immune from IgE-sensitized mechanism mast cells and basophils Anaphylaxis Allergic rhinitis Clinical Allergic asthma Examples Food allergies Urticaria tests for type 1 hypersensitivity 1. IN-VIVO SKIN PRICK Preferred screening test for allergies TEST Very small amounts of potential allergens are injected under the skin Positive result: wheal-and-flare reaction after 20 minutes tests for type 1 hypersensitivity 2. RADIOALLERGOSORBENT Sample: TEST (RAST)patient serum. A form of radioimmunoassay A form of allergen-specific IgE testing 3. RADIOIMMUNOSORBENT TEST First test developed for (RIST) the measurement of total IgE. Type II hypersensitivity Also known as antibody-mediated cytotoxic hypersensitivity. Involves IgG and IgM antibodies directed against antigens found on cell surfaces. type Ii hypersensitivity reaction immune IgG or IgM mediator synonym Antibody mediated cytotoxicity Timing Immediate Cell surface: Antigen autologous or heterologous Complement YES involvement Cell destruction caused by antibody and complement, opsonization, ADCC. Immune Cell function mechanism inhibited by antibody binding. Cell function type Ii hypersensitivity reaction Transfusion reactions Autoimmune hemolytic anemia Hemolytic disease clinical of the newborn examples Drug reactions Myasthenia gravis Goodpasture's syndrome Graves disease Type IIi hypersensitivity Also known as immune complex hypersensitivity. Almost similar to type lI, except that in type IlI the antigens are soluble type III hypersensitivity reaction immune IgG or IgM mediator synonym Complex-mediated Timing Immediate Antigen Soluble: heterologous or autologous Complement YES involvement Antigen-antibody complex activate complement Immune proteins. mechanism Neutrophils are recruited and release lysosomal enzymes that cause type Ii hypersensitivity reaction Serum sickness Arthus reaction Lupus clinical erythematosus examples Rheumatoid arthritis Drug reactions arthus reaction Immune complexes are formed and deposit on walls of blood vessels, activating complement. serum sickness Results from passive immunization of humans with animal serum. Human develops antibodies against protein in the animal serum, antibodies combine with the protein forming complexes that can deposit in the tissues. Type Iv hypersensitivity First described by Robert Koch. Differs from the first three in that sensitized Tcells, rather than antibodies, play a major role. Also known as delayed hypersensitivity (because symptoms peak between 48 hours to 72 hours). type IV hypersensitivity reaction immune T cells mediator synonym Cell mediated or delayed type Timing Delayed Antigen Autologous or heterologous Complement No involvement Antigen-sensitized Th1 cells release cytokines that recruit Immune macrophages and mechanism induce inflammation or activate cytotoxic T type Ii hypersensitivity reaction Contact dermatitis Tuberculin skin test clinical Allergy skin test examples Hypersensitivity pneumonitis CONTACT DERMATITIS Usually caused by low- molecular-weight compounds that touch the skin. Most common cause includes poison ivy, poison oak, and poison sumac (due to the chemical urushiol in the plant sap). Other agents: Nickel, rubber, formaldehyde,