CD40LG and cold agglutinin disease: Cold agglutinin syndrome (CAS) is a group of syndromes characterized by chronic hemolytic anemia and microembolism caused by autoreactive hemagglutination and cold-induced factors.[1] Cold agglutinin antibodies are mainly immunoglobulin M (IgM), which can act on their own red cell antigens and lead to reversible hemagglutination when the environmental temperature is <21°C.