TypIIIHypersensitivität

TypIIIHypersensitivität, also known as immune complex-mediated hypersensitivity, is an immunological reaction that occurs when antigens and antibodies form complexes in the circulation. These immune complexes, if not cleared efficiently by phagocytic cells, can deposit in various tissues. This deposition triggers an inflammatory response, primarily mediated by the complement system and the recruitment of neutrophils.

The process begins with the formation of antigen-antibody complexes. When these complexes lodge in the small blood vessels of organs like the kidneys, joints, or skin, they activate the complement cascade. This activation leads to the generation of anaphylatoxins (C3a and C5a), which are potent chemoattractants for neutrophils. Neutrophils then attempt to phagocytose these immune complexes, releasing lysosomal enzymes and reactive oxygen species in the process. This enzymatic and oxidative damage to the host tissue is the hallmark of Type III hypersensitivity.

Clinical manifestations vary depending on the site of immune complex deposition. Examples include serum sickness, a systemic reaction to foreign proteins; Arthus reaction, a localized inflammatory response at an injection site; and certain autoimmune diseases like lupus nephritis. Diagnosis often involves detecting circulating immune complexes or specific antibodies and antigens in affected tissues. Treatment focuses on reducing inflammation and suppressing the immune response, typically with corticosteroids and immunosuppressive agents.