PADI4 and periodontitis: Similarly to the protein expression of PAD2 and PAD4, the mRNA expression of PADI2 and PADI4, assessed by qPCR analysis, was also significantly higher (p < 0.05 and p < 0.01, respectively) in the gingival tissue of patients with periodontitis compared to healthy controls without periodontitis (Fig. 4e, f).