Previous flow-cytometry studies primarily examined PD-1 expression in peripheral blood T cells in RA, yielding conflicting results, especially in CD4+T and CD8+ T cell populations with most of the evidence, however, supporting the increased expression of PD-1 compared to healthy individuals or patients with osteoarthritis (14, 15, 17, 31). The gene discussed is CD4; the disease is rheumatoid arthritis.