Among known classical complement receptors (CR), only type 1 complement receptor (CR1/CD35) was shown to bind both C4b and C3b fragments of cleaved C4 and C3 using two different domains for C4b and C3b, and this receptor is associated with the pathogenesis of certain autoimmune diseases (Khera and Das, 2009). This evidence concerns the gene C4A and autoimmune disease.