Early in 1996, Neidhart et al. demonstrated that RA patients had elevated proportions of CD4+ T cells, which were correlated with the clinical parameters of disease activities.24 Subsequent studies gradually recognized an important role for Tm cells in the pathogenesis of autoimmune diseases such as RA, which was likely related to aberrant T-cell activation, leading to a surge in the number of Tm cells.25–27 In the present study, we found that RA patients manifested a predominantly high number of Tm cells in both SF and the peripheral blood. Here, CD4 is linked to autoimmune disease.