Complement deficiencies

The complement system comprises a group of heat-labile proteins which form part of the innate immune system. The main physiological functions of the complement system include defence against pyogenic bacterial infections, clearance of immune complexes and products of inflammatory damage, and acting as a bridge between the innate and adaptive immune system. The complement system is regulated by various complement inhibitors (regulatory proteins) that are present in both the classical pathway and the alternate pathway and which regulate and prevent spontaneous activation of the complement system, thereby preventing complement-mediated damage to tissues under normal circumstances. This chapter addresses the clinical features, diagnosis, and management of inherited and acquired deficiencies of complement proteins or inhibitors.