PFN1 and rheumatoid arthritis: We constructed the logistic regression model and the random forest model based on the selected nine genes including CFL1, COTL1, ACTG1, PFN1, LCP1, LCK, HLA-E, FYN, and HLA-DRA in the PPI network, in which the expression of selected nine genes served as the continuous predict variable and the sample type (RA or not) served as the response variable.