Allergic reaction and allergy, refers to the body from the antibody ( including hapten ) after stimulation, produce corresponding antibody or lymphocyte sensitization, when once again contact with an antigen after in vivo induced humoral or cellular immune responses, resulting in tissue damage or physiological dysfunction. Allergic reactions are generally divided into four types: ( 1) allergic reaction type is also called speed sensitive type, IgE dependent reaction, the reaction is due to antigen and IgE antibody interactions arising from the. Cause local smooth muscle spasm, increase vascular permeability, capillary dilatation and congestion, edema and histological changes of plasma extravasation. Belongs to the type I allergy skin disease urticaria, angioedema, etc.. ( 2) type II hypersensitivity reaction is also called the cytotoxic reaction, is produced on the cell body composition or anchored to the cell antigen antibody, when compared with the corresponding antigen antigen-antibody reaction, because the complement in the cell lysis or tissue injury. Belong to the type II hypersensitivity skin disease drug anemia, thrombocytopenia purpura, pemphigus. Pemphigoid. ( 3)Ⅲtype allergic reaction called the immune complex type reaction, immune complexes refers to some antigen produced antibody and the antigen settlement formation of antigen-antibody complexes, the compound is relatively easy composure on the vascular wall basement membrane and its surrounding, with walls of small blood vessels in change of heart, thus occurrence of organ and tissue damage. Belongs to the type III hypersensitivity skin has allergic vasculitis, lupus nephritis, the serum disease. ( 4) type IV hypersensitivity and delayed hypersensitivity reaction, the reaction is due to the body after it is stimulated by antigens, T lymphocyte transformation to the corresponding sensitized lymphocytes, when the cell is again encountered the corresponding antigen, often in 1-2 days after releasing a series of lymphokines, cause tissue damage or directly on the target cell destruction. Belong to type IV allergy skin disease with contact dermatitis, eczema, tuberculin skin reaction.
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