CD4 and rheumatoid arthritis: Our observation of a small but significant increase in the frequency of IL-17-producing CD4 T cells in SF compared to peripheral blood of RA patients, and the same for the frequency of memory CD4 T cells (CD45RO-positive) producing IL-17, are consistent with data from Shahrara et al. [26] but differ from the findings of Yamada et al. [28].