CD28 and psoriatic arthritis: Abatacept, a CTLA-4Ig costimulatory blockade that interferes with CD28 on T cells binding to CD80/CD86 on APCs, has shown efficacy in clinical trials for RA [16] (which has become one of the established treatments), psoriatic arthritis [17], and juvenile idiopathic arthritis [18], among other autoimmune diseases.