On the other hand, a study found that CCR9 expression on Tregs from spleen and draining lymph nodes of either normal or collagen-induced arthritis mice was undetectable.[29] Another study indicated that binding of CCR9 to CCL25 inhibits the differentiation of CD4+ T cells differentiating to Tregs in vitro.[30] Consistent with these results, this study showed positively correlated between CCR9+CD4+ T cells and IL-6, IL-17A as well as disease activity, which provide more clarity on the pro-inflammatory role of CCR9+CD4+ T cells in RA. Here, IL17A is linked to rheumatoid arthritis.