TGFB1 and rheumatoid arthritis: Together with our result with proinflammatory cytokines, these data suggest that in an IL‐2‐limited but TGF‐β‐rich and proinflammatory cytokine‐rich environment such as inflamed joints of RA 23, 24, CXCL13‐producing CD4+ T cells and Th17 cells, rather than FoxP3hi cells, may preferentially differentiate and exert their function.