The hypercitrullination observed in periodontitis mirrors the citrullinome of RA, which is most likely induced by Aggregatibacter actinomycetemcomitans through its pore-forming toxin, leukotoxin A [17], or by the prokaryote PAD-expressing oral pathogen Porphyromonas gingivalis [18]. Here, PADI4 is linked to periodontitis.