Comparison of the ratio between sOX40 and sOX40L in early rheumatoid arthritis (eRA) and chronic rheumatoid arthritis (cRA). The ratio was significantly lower in patients with eRA than in patients with cRA. Healthy volunteers are not included as many of the measurements for both sOX40 and sOX40L were below the level of detection. Paired data (within the eRA group) were analyzed by the Wilcoxon signed-rank test and non-paired data were analyzed by the Mann-Whitney U-test. Boxes represent median with interquartile range and whiskers represent the 5th to 95th percentiles. *P <0.05, ***P <0.001.