PADI4 and rheumatoid arthritis: In RA, citrullination is identified in relation to intestinal permeability and microbial imbalance [173], and it must furthermore be considered that many other microbes may be able to cause citrullination of proteins in their hosts (both commensals and pathogens) due to bacterial PAD-homologues (ADI) [174,175], and this may contribute to citrullination mediated inflammatory responses exacerbating various pathologies.