- 첨부된 파일이 없습니다.
▶Subject : Hypersensitivity Reactions
▶Speaker : Dr. 장윤석 (Seoul National University Bundang Hosptial)
▶Date : 11:00AM/May.15(Tue)/2012
▶Place : conference room (1F),PBC
When a host meets an antigen, the host may show no response (tolerance), immunity (beneficial response) or hypersensitivity reactions (harmful response). Current understanding of the pathophysiologic mechanisms of hypersensitivity reactions is mainly based on the Gell and Coombs classification, which was proposed in 1963.
Type I (IgE-mediated) hypersensitivity can be induced by allergens via allergen-specific IgE, IgE-binding Fc receptors, mast cells and basophils. Histamine and several mediators play key role in type I hypersensitivity reaction. Typical examples are anaphylaxis, urticaria, angioedema, allergic rhinitis, and asthma.
Type II (antibody-mediated cytotoxic) hypersensivity can be induced by antibodies that are directed against cell surface antigens, which mediate cell destruction via complement activation or antibody-dependent cell-mediated cytotoxicity. Typical examples are blood transfusion reactions, erythroblastosis fetalis, and autoimmune hemolytic anemia.
Type III (immune complex-mediated) hypersensitivity can be induced by antigen-antibody complexes deposited in various tissues which induce complement activation and inflammatory responses mediated by massive infiltration of neutrophils. Typical examples are localized Arthus reaction, serum sickness, necrotizing vasculitis, glomerulonephritis, and systemic lupus erythematosus.
Type IV (cell-mediated) hypersensitivity can be induced by sensitized T cells which release cytokines that activate inflammatory cells or by cytotoxic T cells which mediated direct cellular damage. Typical examples are contact dermatitis, tuberculoma, and graft rejection.
Recently a modified Gell and Coombs classification of hypersensitivity reactions has been widely accepted. Type II hypersensitivity reaction which is mediated by antibodies now is classified into type IIa (classical antibody-mediated cytotoxic) and IIb (functional antibody-mediated) hypersensitivity reactions. Type IV hypersensitivity reaction which is mediated by T cell is now classified into IVa1 (Th1 mediated), IVa2 (Th2 mediated), and IVb (cytotoxic T mediated).
It is important to understand the pathophysiology of hypersensitivity reactions which eventually induce clinical symptoms and diseases.
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