CTLA4 and systemic lupus erythematosus: Although SLE T cells have impaired interleukin-2 (IL-2) production and proliferative response to stimulation of the T cell receptor-CD3 compound[3,4], expression of costimulatory molecules such as CD40L and CTLA4, which is essential for lymphocyte activation [5,6], is up-regulated [7-10].