And by analyzing the differential ability of MUC5AC between CTD-non ILD and CTD-ILD, the AUC value of MUC5AC reached 0.78, which has a good ability to distinguish whether CTD patients have ILD disease, While the AUC value of MUC5B was only 0.68(Supplementary Figure 1). The gene discussed is MUC5B; the disease is interstitial lung disease.