Role of complement in innate and autoimmunity.

The complement system is a major driver of our innate immune response and plays an important role in defence against foreign pathogens. It is composed of a large number of proteins that are found in the circulation, in tissues and other body fluids in pro-enzymatic form. The many biologic activities of the complement system are uncovered following activation by three known pathways. Together with phagocytic cells the complement system is a powerful tool to defend the host against foreign attack. However the complement system, under certain conditions, can be unfavorable to the host namely in diseases such as IgA nephropathy, systemic lupus erythematosus and in diseases where minor changes have occurred in the integrity of tissue such as in ischemia reperfusion. This review describes the many faces of complement in the field of innate and acquired immunity and takes the reader on a journey of the role of complement in health and disease.