IL4I1 and rheumatoid arthritis: To verify the prediction performance of the candidate biomarkers (IL17F, 5-HT and IL4I1 for RA-Cold; S1P and GLNS for RA-Hot) in clinical diagnosis of the two groups, we carried out ELISA and ROC analyses to detect the levels of the candidate biomarkers in serum and synovial fluid samples from the independent clinical cohort.