A Secreted Bacterial Peptidylarginine Deiminase Can Neutralize Human Innate Immune Defenses.

The keystone oral pathogen Porphyromonas gingivalis is associated with severe periodontitis. Intriguingly, this bacterium is known to secrete large amounts of an enzyme that converts peptidylarginine into citrulline residues. The present study was aimed at identifying possible functions of this citrullinating enzyme, named Porphyromonas peptidylarginine deiminase (PPAD), in the periodontal environment. The results show that PPAD is detectable in the gingiva of patients with periodontitis, and that it literally neutralizes human innate immune defenses at three distinct levels, namely bacterial phagocytosis, capture in neutrophil extracellular traps (NETs), and killing by the lysozyme-derived cationic antimicrobial peptide LP9. As shown by mass spectrometry, exposure of neutrophils to PPAD-proficient bacteria reduces the levels of neutrophil proteins involved in phagocytosis and the bactericidal histone H2. Further, PPAD is shown to citrullinate the histone H3, thereby facilitating the bacterial escape from NETs. Last, PPAD is shown to citrullinate LP9, thereby restricting its antimicrobial activity. The importance of PPAD for immune evasion is corroborated in the infection model Galleria mellonella, which only possesses an innate immune system. Together, the present observations show that PPAD-catalyzed protein citrullination defuses innate immune responses in the oral cavity, and that the citrullinating enzyme of P. gingivalis represents a new type of bacterial immune evasion factor.IMPORTANCE Bacterial pathogens do not only succeed in breaking the barriers that protect humans from infection, but they also manage to evade insults from the human immune system. The importance of the present study resides in the fact that protein citrullination is shown to represent a new bacterial mechanism for immune evasion. In particular, the oral pathogen P. gingivalis employs this mechanism to defuse innate immune responses by secreting a protein-citrullinating enzyme. Of note, this finding impacts not only the global health problem of periodontitis, but it also extends to the prevalent autoimmune disease rheumatoid arthritis, which has been strongly associated with periodontitis, PPAD activity, and loss of tolerance against citrullinated proteins, such as the histone H3.

Stobernack T ，du Teil Espina M ，Mulder LM ，Palma Medina LM ，Piebenga DR ，Gabarrini G ，Zhao X ，Janssen KMJ ，Hulzebos J ，Brouwer E ，Sura T ，Becher D ，van Winkelhoff AJ ，Götz F ，Otto A ，Westra J ，van Dijl JM ... -  《mBio》

Conserved Citrullinating Exoenzymes in Porphyromonas Species.

Gabarrini G ，Chlebowicz MA ，Vega Quiroz ME ，Veloo ACM ，Rossen JWA ，Harmsen HJM ，Laine ML ，van Dijl JM ，van Winkelhoff AJ ... -  《-》

Periodontal sources of citrullinated antigens and TLR agonists related to RA.

Vitkov L ，Hannig M ，Minnich B ，Herrmann M ... -  《-》

Extracellular Proteome and Citrullinome of the Oral Pathogen Porphyromonas gingivalis.

Stobernack T ，Glasner C ，Junker S ，Gabarrini G ，de Smit M ，de Jong A ，Otto A ，Becher D ，van Winkelhoff AJ ，van Dijl JM ... -  《-》

Heightened immune response to autocitrullinated Porphyromonas gingivalis peptidylarginine deiminase: a potential mechanism for breaching immunologic tolerance in rheumatoid arthritis.

Quirke AM ，Lugli EB ，Wegner N ，Hamilton BC ，Charles P ，Chowdhury M ，Ytterberg AJ ，Zubarev RA ，Potempa J ，Culshaw S ，Guo Y ，Fisher BA ，Thiele G ，Mikuls TR ，Venables PJ ... -  《-》