The frequency of IL-1RI-expressing cells was significantly higher in ex vivo memory CD4+ T cells derived from synovial fluid (16.35 ± 1.70%) and peripheral blood (14.49 ± 1.20%) of RA patients compared with counterpart cells (7.11 ± 0.85%; p<0.001) from age-match healthy controls (HCs) (Figure 7A and B). Here, CD4 is linked to rheumatoid arthritis.