IL4I1 and rheumatoid arthritis: As shown in Fig. 6A, B, IL17F, 5-HT and IL4I1 levels were significantly different in RA-Cold patients than that in NC and RA-Hot patients (all P < 0.05, AUC > 0.7), whereas the differences in the content of S1P and GLNS in RA-Hot patients were significantly different from those in NC group and RA-Cold patients (all P < 0.05, AUC > 0.7), indicating their potential role in the classification of the two RA patient groups.