Immune Complexes: Normal Physiology and Role in Disease

It has been known for over 100 years that immune complexes can cause severe organ pathology. Many investigators have studied mechanisms of immune complexes mediated tissue destruction and how they contribute to the development of autoimmunity, but many critical aspects about immune complex function in causing disease are still unknown. The predisposing factors that govern immune complex tissue deposition and whether or not circulating immune complexes participate in tissue pathology all remain unclear at this time. Nevertheless, a great deal has been learned. It is known that many of the pathological effects of immune complexes are due to their ability to activate complement and bind IgG Fc? receptors. It has been well documented that Fc? receptors may either promote or down-regulate the pathological effects induced by immune complexes. The constituents of immune complexes are also well-defined demonstrating that the isotype and subclass of antibody within the immune complex as well as the nature of the antigen itself all play key roles in pathology. Mediators induced by immune complexes have also been discovered and have been shown to influence pathology. There have been many animal models of disease developed and studied in great detail allowing scientists to understand the mechanisms of clearance of immune complexes from the body. This brief review attempts to clarify the course of events known to take place during immune complex disease and review the basic knowledge gained over the last century.