CD4 and rheumatoid arthritis: To investigate the status of circulating Tfh and Tfr cells, we detected the frequencies of CD4+CXCR5+Foxp3− Tfh and CD4+CXCR5+Foxp3+ Tfr cells, which were gated from CD3+CD4+ T cells in a flow cytometry analysis of patients with RA and HCs (Additional file 1: Figure S1A, B).