Immunoglobulin in the control of complement action

Complement is a critical element of innate immunity, protecting individuals from a wide variety of microbial infections. This group of proteins is res ponsible for many features of inflammation and tissue damage. Because of it s ability to mediate autoimmune tissue damage and to destroy host tissues, it is under tight regulation with many circulating and cell-membrane-bound complement regulatory proteins. The function of much of the circulating imm unoglobulin has never been defined. We have advanced the hypothesis that on e function of circulating immunoglobulin is to down-regulate complement att ack on host tissues in the presence of anti-self antibody. The data to supp ort this hypothesis are reviewed. The data are consistent with the suggesti on that one mechanism of action of intravenous immunoglobulin, used to trea t patients with a variety of autoimmune diseases, is prevention of compleme nt-mediated attack on host tissues.