In humans, a regulatory polymorphism in PD-1 is associated with susceptibility to systemic lupus erythematosus and multiple sclerosis (Prokunina et al., 2002; Kroner et al., 2005), while polymorphisms of the CTLA-4 have been linked to multiple autoimmune diseases including asthma, systemic lupus erythematosus, Graves’ disease, and autoimmune thyroid diseases (Kristiansen et al., 2000). Here, CTLA4 is linked to systemic lupus erythematosus.