Deficiencies in the classical pathway of the complement system have been implicated in the aetiology and pathogenesis of autoimmune diseases such as SLE.9 Human complement receptor 1 (CR1, CD35) is an integral membrane complement control protein (CCP) whose primary role on erythrocytes is the non-inflammatory clearance of immune complexes opsonised with C3a and C4b. The gene discussed is CR1; the disease is systemic lupus erythematosus.