immune complex disease(redirected from type III hypersensitivity reaction)
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Immune complex disease
Local or systemic tissue injury caused by the vascular deposition of products of antigen-antibody interaction, termed immune complexes. Immune complex formation with specific antibodies causes the inactivation or elimination of potentially harmful consequences only when immune complexes deposit in tissues, inciting various mediators of inflammation. When the reaction takes place in the extravascular fluids near the site of origin of the antigen (by injection, secretion, and such), focal injury can occur, as exemplified by the Arthus reaction or such conditions as experimental immune thyroiditis. Systemic disease may occur when soluble antigens combine with antibodies in the vascular compartment, forming circulating immune complexes that are trapped nonspecifically in the vascular beds of various organs, causing such clinical diseases as serum sickness or systemic lupus erythematosus with vasculitis and glomerulonephritis. The term immune complex disease usually signifies this systemic immune complex formation and vascular deposition. See Antigen-antibody reaction
Circulating immune complex disease occurs when the host's antibody production, relative to the amount of antigens, is inadequate for prompt elimination of antigen. Normally, excess amounts of antibody are formed which generate large immune complexes that are removed very rapidly from the circulation and are disposed of by the mononuclear phagocytic system. If the antibody response is very poor, only a few very small complexes are formed which are not prone to vascular deposition. When the relative antibody production is such that complexes of intermediate size form, vascular trapping can occur and injury results from the effects of inflammation. In addition to immune complex size, other factors influence vessel deposition, including the efficiency of systemic clearance of immune complexes, the hemodynamics of blood flow, and vasoactive amine-influenced changes in vascular permeability. Through dynamic equilibrium, continual modification of the deposits occurs as antigen and antibody fluctuate in the body fluids.
Treatment of immune complex disease can be divided into nonspecific and more specific modalities. Primary among the specific measures is the identification and elimination of the offending antigen. This may be possible with some infections when specific therapies are available, and in certain instances where the antigenic source can be removed, such as a neoplasm. More frequently, nonspecific anti-inflammatory (corticosteroids) and immunosuppressive agents (such as cyclophosphamide and azathioprine) are used to attempt to blunt the person's immune response, thereby lessening the amount of immune complexes produced. See Autoimmunity, Immunology