CD4 and rheumatoid arthritis: Despite the low frequency of IL-17-positive CD4 T cells coexpressing IL-22, the frequency of IL-22-positive CD4 T cells correlated strongly with the frequency of IL-17-producing CD4 T cells in PBMC of RA patients (r = 0.57, P < 0.0004); this correlation was not evident in SFMC (r = 0.35, P = 0.22).