Proteolytic manipulation of neutrophil responses and the efferocytic synapse by porphyromonas gingivalis.

Porphyromonas gingivalis (Pg) is etiologically associated with chronic periodontitis, a highly prevalent chronic inflammatory disease characterized by the destruction of hard and soft tissues of the periodontium. Pg is adapted to live in the human oral subgingival niche, a hostile environment dominated by excessive numbers of activated neutrophils and antimicrobial mediators. Its survival is contingent upon prompt and effective inactivation of neutrophil effector functions. In this dissertation, I uncover a novel pathogenic mechanism employed by Pg that disarms the antimicrobial capacity of live neutrophils and simultaneously sequesters them within macrophages. Mechanistically, RgpB, a cysteine protease produced by Pg proteolytically, modifies the intracellular and extracellular proteins of neutrophils, thus dysregulating neutrophil function. RgpB-exposed neutrophils support intracellular bacterial survival because of compromised antimicrobial capacity due to RgpB-mediated degradation of intracellular microbicidal compounds and depleted phagosomal oxidative burst. Interestingly, RgpB-mediated remodeling of the neutrophil proteome does not induce apoptosis but causes significant remodeling of the neutrophil proteome, resulting in alterations to a repertoire of proteins on the neutrophil surface. The neutrophil surface becomes decorated with degraded neutrophil granule proteins that engage macrophage integrin receptors, resulting in the atypical efferocytosis of live neutrophils. Macrophages that sequester these live RgpB imprinted neutrophils in their efferosomes become transcriptionally and phenotypically dysregulated and produce inflammatory cytokines that prevent the resolution of inflammation in vivo. My work uncovers a vicious inflammatory cycle perpetuated by a previously undescribed mechanism employed by Pg and underscores the potential for developing novel therapeutic strategies that target this unique virulence mechanism.