The first two important variables of each model were selected according to the ranking of importance, and the final identified key genes for RA immune heterogeneity were IFNG, IL7R, CCR7, KLRB1, CXCL9, CXCL13, SELL, and PTPRC (Fig. 3B–E). The gene discussed is CXCL13; the disease is rheumatoid arthritis.