PADI4 and rheumatoid arthritis: The PAD4 activity was negatively correlated with the frequency of IL-6-producing monocytes (before and after stimulus) in the PERIO+RA group (r = −0.758; p = 0.002; r = −0.569; p = 0.017) and also in PERIO group, but only before stimulus (r = −0.833, p = 0.005).