PADI4 and rheumatoid arthritis: Our study was not designed to examine sputum anti-PAD4 antibodies in RA-related lung diseases, but our confirmation in this study that these antibodies can be present in the lung supports future studies that can specifically address whether sputum anti-PAD4 or anti-PAD3/4 antibodies are associated with the prevalence, severity, or future development of RA-related lung diseases.