The main finding in the present study was that both citrullination and expression of endogenous PADs (PAD2 and PAD4), both at mRNA and protein level, are increased in gingival connective tissue of patients with periodontitis compared to periodontally healthy controls independently of the presence of the periodontal pathogen P. gingivalis or leukotoxin of A. actinomycetemcomitans. Here, PADI4 is linked to periodontitis.