CD4 and rheumatoid arthritis: Previous studies have demonstrated increased numbers of activated CD69+CD4+ T cells in the peripheral blood and augmented infiltration in the synovial tissue of RA patients.6, 7 Interestingly, the majority of these accumulated activated CD69+CD4+ T cells in the synovial fluid (SF) were memory T (Tm) cells,8 indicating the continuous hyper-activation of Tm cells in RA patients, although the different factors responsible for this elevation are not satisfactorily understood.