Hypersensitivity Types and Their Mechanisms Type I - lgE - Soluble antigen - Allergen-specific lgE antibodies bind to mast cells via their Fc receptor. When the specific allergen binds to the lgE, cross-linking of lgE induces degranulation of mast cells. - Local and systemic anaphylaxis, seasonal hay fever, food allergies, and drug allergies Type II - IgG or IgM - Cell-bound antigen - IgG or IgM antibody binds to cellular antigen, leading to complement activation and cell lysis. IgG can also mediate ADCC with cytotoxic T cells, natural killer cells, macrophages, and neutrophils. - Red blood cell destruction after transfusion with mismatched blood types or during hemolytic disease of the newborn. Type Ill - IgG and IgM - Soluble antigen - Antigen-antibody complexes are deposited in tissues. Complement activation provides inflammatory mediators and recruits neutrophils. Enzymes released from neutrophils damage tissue. - Post-streptococcal glomerulonephritis, rheumatoid arthritis, and systemic lupus erythematosus Type IV - T cells - Soluble or cell-bound antigen - TH1 cells secrete cytokines, which activate macrophages and cytotoxic T cells. - Contact dermatitis, type I diabetes mellitus, and multiple sclerosis #Hypersensitivity #Types #Classification #Pathophysiology #Allergy #Diagnosis #Reactions #Table
