The complement system plays a central role in rheumatic and autoimmune diseases, several of which are associated with the presence in blood of cold-perceptible immune complexes enriched in IgM RF, specific antibody activities, putative antigens and C1q as part of a cascade capable of activating the classical pathway, leading in turn to the generation of anaphylatoxins, chemotactic factors, and inflammatory mediators. This evidence concerns the gene CD40LG and autoimmune disease.