PADI4 and rheumatoid arthritis: Moreover, recently, the pore-forming leukotoxin (LtxA), secreted by A. actinomycetemcomitans, was shown to be capable of triggering the activation of endogenous PAD in neutrophils through the disruption of the cell membrane and increased cellular calcium influx [15], suggesting that this pathogen could be another candidate bacteria for gingival citrullination triggering autoimmunity in RA.