Abnormalities in the function, regulation, and interactions of immune cells, such as those caused by the overexpression of the costimulators CD70, CD40L, CD84, and SAP in SLE CD4+ T cells, induce autoantibody production in B cells, the loss of self-tolerance, and the synthesis of proinflammatory cytokines, such as IL-4, IL-6, and IL-10. The gene discussed is SH2D1A; the disease is systemic lupus erythematosus.