PADI4 and rheumatoid arthritis: In this first investigation of the relationship between the recently discovered RA-specific auto-antibody, anti-PAD3/4XR, and radiographic ILD, we detected a robust association for both the presence and extent of RA-ILD among patients with anti-PAD3/4XR compared with patients with no anti-PAD antibodies and even among those with anti-PAD4 antibodies that did not cross-react with PAD3.