Clinical Utility of Complement Assessment

Via its multiple functional activities, the complement system plays a major role in host defense against infection and in inflammatory processes. The system consists of more than 25 self-assembling proteins divided into three groups (classical pathway, alternative pathway, and terminal sequence; Table 1), as well as a series of receptors and regulatory proteins. These components act in series and in parallel to achieve several important functions (52, 84, 86). The sequence of complement activation has been reviewed extensively elsewhere (57, 86) and is summarized in Fig. 1.