PADI4 and rheumatoid arthritis: This theory is supported by the observations that PAD2 levels in synovial fluid correlate with total PAD activity and disease activity in rheumatoid arthritis [49], PAD2−/− mice have less central nervous system citrullination in experimental autoimmune encephalomyelitis [41], and PAD2 has less restrictive substrate specificity than PAD4 [50].