Type III, or immune-complex, reactions are characterized by tissue damage caused by the activation of complement in response to antigen-antibody (immune) complexes that are deposited in tissues. The classes of antibody involved are the same ones that participate in type II reactions—IgG…

Type III reactions result when a person who has been strongly sensitized to a particular antigen is subsequently exposed to that antigen. In a type III reaction, the antigen-antibody complex becomes deposited on the walls of the small blood vessels. The complex then triggers the…

Type III, or immune-complex, reactions are directed against soluble antigens. Circulating antibodies combine with antigens, usually not bound to the cell surface, to form an immune complex, which is deposited in tissues or the walls of blood vessels. The complex attracts complement, to which polymorphonuclear…

…a third type of allergy, immune-complex hypersensitivity, the allergen-IgG complex precipitates in tissues, resulting in inflammation via complement fixation. Immune-complex hypersensitivity in the kidney results in an inflammatory injury of the glomeruli (glomerulonephritis), and in the lung it leads to a pneumonia-like condition known as hypersensitivity pneumonitis.