PADI4 and rheumatoid arthritis: In RA tissue (Fig. 10f), but not in OA (Fig. 10e), cytoplasmic PAD4 expression was detected in macrophage-like synoviocytes both in the synovial lining and sublining layers and endothelium of blood vessels, also few positive cells were seen in deeper layers (Figs. 6e, 7e and 9e).