Th17 S1PR1 expression in lymph nodes in early collagen-induced arthritis. DBA/1 mice were ovariectomized, subjected to collagen-induced arthritis (CIA) and treated with 17β-estradiol (E2; 0.83 μg/day) or placebo. (A–C) Frequency of sphingosine-1-phosphate receptor 1-positive (S1PR1+) cells of T helper 17 (Th17) (A) and median fluorescence intensity (MFI) of S1PR1 on Th17 cells (B,C) in lymph nodes (LNs) from CIA mice (day 14, single experiment with n = 10 mice/group). (B) Representative fluorescence-activated cell sorting analysis plot where fluorescence minus one is used as a control. (D) S1P levels in serum of mice with CIA at day 14 were determined by enzyme-linked immunosorbent assay (single experiment, n = 9 or 10 mice/group). To improve normal distribution of data, some data were log-transformed prior to statistical analysis (A,C). Bars or lines show arithmetic mean ± SEM. Student’s t-test (**P <0.01).