The mean ± SEM proportions of total live CD4+ T cells expressing OX40 were 1.5 ± 0.5%, 2.8 ± 1.1%, 1.6 ± 0.3%, and 2.7 ± 0.8% in patients with SpA, B27+ healthy controls, B27− healthy controls, and patients with RA, respectively. This evidence concerns the gene TNFRSF4 and rheumatoid arthritis.