A Secreted Bacterial Peptidylarginine Deiminase Can Neutralize Human Innate Immune Defenses
Tim Stobernack,
Marines du Teil Espina,
Lianne M. Mulder,
Laura M. Palma Medina,
Dillon R. Piebenga,
Giorgio Gabarrini,
Xin Zhao,
Koen M. J. Janssen,
Jarnick Hulzebos,
Elisabeth Brouwer,
Thomas Sura,
Dörte Becher,
Arie Jan van Winkelhoff,
Friedrich Götz,
Andreas Otto,
Johanna Westra,
Jan Maarten van Dijl
Affiliations
Tim Stobernack
Department of Medical Microbiology, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands
Marines du Teil Espina
Department of Medical Microbiology, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands
Lianne M. Mulder
Department of Medical Microbiology, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands
Laura M. Palma Medina
Department of Medical Microbiology, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands
Dillon R. Piebenga
Department of Medical Microbiology, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands
Giorgio Gabarrini
Department of Medical Microbiology, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands
Xin Zhao
Department of Medical Microbiology, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands
Koen M. J. Janssen
Department of Oral and Maxillofacial Surgery, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands
Jarnick Hulzebos
Department of Rheumatology and Clinical Immunology, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands
Elisabeth Brouwer
Department of Rheumatology and Clinical Immunology, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands
Thomas Sura
Institute for Microbiology, Ernst-Moritz-Arndt-University Greifswald, Greifswald, Germany
Dörte Becher
Institute for Microbiology, Ernst-Moritz-Arndt-University Greifswald, Greifswald, Germany
Arie Jan van Winkelhoff
Department of Medical Microbiology, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands
Friedrich Götz
Microbial Genetics, Interfaculty Institute of Microbiology and Infection Medicine and Infection Medicine (IMIT), University of Tübingen, Tübingen, Germany
Andreas Otto
Institute for Microbiology, Ernst-Moritz-Arndt-University Greifswald, Greifswald, Germany
Johanna Westra
Department of Rheumatology and Clinical Immunology, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands
Jan Maarten van Dijl
Department of Medical Microbiology, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands
ABSTRACT 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.
