CD28 and rheumatoid arthritis: To clearly confirm the suppression of SIGIRR on TNF-α expression in memory CD4+ T cells ex vivo, RA SIGIRR− memory CD4+ T cells from PBMCs were flow-sorted and transduced with retroviral empty vectors (empty) or vectors encoding SIGIRR (SIGIRR overexpression) and treated with IL-1β in the presence of α-CD3/α-CD28 antibodies for 48 h.