The complement system is a principle mediator of inflammation and serves as an important arm of the body's immune response. It was first discovered as a heat-sensitive serum factor necessary for bacterial lysis in the presence of specific antibody. How it "complements" the antigen-antibody interaction and mediates inflammation has been the subject of intensive research.
The complement system consists of 19 well-defined plasma proteins that interact with each other and with cell membranes. The function of many of these proteins has been defined through the study of natural deficiency states.—the primary, inherited complement deficiencies. While much has been written about these,1-4 there has been relatively little work addressing secondary disorders of complement. The purpose of this article is to survey diseases in which complement deficiency is secondary to some more primary disorder (Table 1). In most cases the complement deficiency contributes to the clinical presentation or pathogenesis of the
Eichenfield LF, Johnston RB. Secondary Disorders of the Complement System. Am J Dis Child. 1989;143(5):595–602. doi:10.1001/archpedi.1989.02150170097032