Flow cytometry analysis of in vitro cultured CD4+ T cells confirmed the increase in Th17 cell frequencies in patients with AS or RA (5.03 ± 0.5% in AS vs. 2.4 ± 0.47% in HC, p = 0.0027; 9.1 ± 0.98% in RA; Fig. 1f) and the EP4 receptor overexpression in AS (MFI 13.5 ± 1.5 in AS vs. 8.7 ± 0.45 in HC, p = 0.0139; Fig. 1g). The gene discussed is CD4; the disease is rheumatoid arthritis.