Complement factor H: Physiology and pathophysiology

The human plasma protein factor I-I, which is a multifunctional, multidomai n protein, acts as a central regulator of the complement system. In additio n to its complement regulatory activities, factor H has multiple physiologi cal activities and 1) acts as an extracellular matrix component, 2) binds t o cellular receptors of the integrin type, and 3) interacts with a wide sel ection of ligands, such as the C-reactive protein, thrombospondin, bone sia loprotein, osteopontin, and heparin. Recent genetic reports, which show inv olvement of factor H in the human disease hemolytic-uremic syndrome (HUS), have attracted the attention of both clinicians and basic complement resear chers to the role of factor II in the pathophysiology of HUS.