Of note, we observed a mild increase in PADI4 expression in RA-ILD lung but not in isolated fibroblasts (Supplementary Fig. S1A and S1B online); however, no difference in PADI1, PADI3, and PADI6 expression was observed between RA-ILD and control lung (Supplementary Fig. S1A online). Here, PADI4 is linked to rheumatoid arthritis.