CD4 and rheumatoid arthritis: (C and D) Representative flow cytometric plot (C) and the frequencies (D) of IL-1RI and IL-1RII expression on TCR-stimulated memory CD4+ T cells from peripheral blood (n = 13) and synovial fluid (n = 5) of RA patients and peripheral blood of HCs (n = 6) at day 2 post-stimulation.