CD4 and rheumatoid arthritis: In both the peripheral blood and SF of RA patients, the majority of CD4 T cells expressed IFNγ (Figure 2A, 2B) with the frequency of IFNγ-positive IL-17-negative T cells significantly higher in the SFMC (77.75% (62.37 to 85.93)) compared to PBMC (59.97% (31.07 to 78.27)) (P = 0.042).