CD4 and rheumatoid arthritis: Among T cells, the PD‐1+CD4+ T cells, including the CXCR5+ TFH and CXCR5− TPH cells, are highly expanded in the inflamed synovium of patients with RA and are intimately involved in the pathogenesis of RA.[5a,b] We first investigated the presence of PD‐1+ T cells in patients with RA.