Therefore, we determined the frequencies of circulating CD4+CXCR5+Foxp3− Tfh and CD4+CXCR5+Foxp3+ Tfr cells, and the expression of PD-1, ICOS, intracellular IL-21 and phosphorylated STAT3 (pSTAT3) in Tfh cells in patients with RA and corresponding healthy controls (HCs). Here, ICOS is linked to rheumatoid arthritis.