Type III hypersensitivity diseases

Although the antibodies in type III hypersensitivity are similar to those in type II hypersensitivity, mainly IgG and IgM antibodies, the difference is that these antibodies specifically bind to corresponding soluble antigens to form antigen-antibody complexes (immune complexes), which under certain conditions deposit in tissues such as the glomerular basement membrane, blood vessel walls, skin, or synovium. The immune complexes activate the complement system, producing anaphylatoxins and attracting neutrophils to infiltrate locally; they cause platelet aggregation, releasing vasoactive amines or forming thrombi; and they activate macrophages to release cytokines such as IL-1. The result is an inflammatory reaction and tissue damage characterized by congestion, edema, local necrosis, and neutrophil infiltration. This type of hypersensitivity is also called immune complex-mediated hypersensitivity.