PADI4 and rheumatoid arthritis: This bacterium triggers hypercitrullination by secreting LtxA, a virulence factor that induces hypercitrullination by disrupting the neutrophil membrane, leading to calcium influx, PAD4 activation, and the release of citrullinated proteins and virulence factors, thereby contributing to autoimmunity in the pathogenesis of RA [21,33,35].