Inactive Gingipains from P. gingivalis Selectively Skews T Cells toward a Th17 Phenotype in an IL-6 Dependent Manner

Abstract

Gingipain cysteine proteases are considered key virulence factors of Porphyromonas gingivalis. They significantly influence antibacterial and homeostatic functions of macrophages, neutrophils, the complement system, and cytokine networks. Recent data indicate the role of P. gingivalis in T cell differentiation; however, the involvement of gingipains in this process remains elusive. Therefore, the aim of this study was to investigate the contribution of danger signals triggered by the gingipains on the generation of Th17 cells, which play a key role in protection against bacterial diseases but may cause chronic inflammation and bone resorption. To this end we compared the effects of the wild-type strain of P. gingivalis (W83) with its isogenic mutant devoid of gingipain activity (ΔKΔRAB), and bacterial cells pretreated with a highly-specific inhibitor of gingipains activity (KYTs). Antigen presenting cells (APCs), both professional (dendritic cells), and non-professional (gingival keratinocytes), exposed to viable bacteria expressed high amounts of cytokines (IL-6, IL-21, IL-23). These cytokines are reported to either stimulate or balance the Th17-dependent immune response. Surprisingly, cells infected with P. gingivalis devoid of gingipain activity showed increased levels of all tested cytokines compared to bacteria with fully active enzymes. The effect was dependent on both the reduction of cytokine proteolysis and the lack of cross-talk with other bacterial virulence factors, including LPS and fimbriae that induce de novo synthesis of cytokines. The profile of lymphocyte T differentiation from naive T cells showed enhanced generation of Th17 in response to bacteria with inactive gingipains. Moreover, we found that gingipain-dependent induction of Th17 cells was highly specific, since other T cell-subsets remained unchanged. Finally, inhibition of IL-6 signaling in dendritic cells led to a significant depletion of the Th17 population. Cumulatively, this study revealed a previously undisclosed role of gingipain activity in the process of Th17 differentiation reliant on blocking signaling through IL-6. Since inactivation of gingipains accelerates the skewing of T cells toward Th17 cells, which are detrimental in periodontitis, IL-6 signaling may serve as an attractive target for treatment of the disease.

Porphyromonas gingivalisand adverse pregnancy outcome

“…More recently, it has been demonstrated that P. gingivalis favors T helper cell polarization to a TH17 profile with generation of TH17-related cytokines [30] and that the P. gingivalis induced T cell differentiation shift is highly specific towards a TH17 cell phenotype in an IL-6 dependent manner [31]. Moreover, a periodontitis rat model study showed a variable sitespecific TH17/Treg cell ratio in the oral tissues but detected a TH17 cell increase with a relative Treg cell decrease in peripheral blood, which was proposed to potentially impact development of systemic inflammatory diseases [32].…”

The Role of Skin and Orogenital Microbiota in Protective Immunity and Chronic Immune-Mediated Inflammatory Disease

“…Inhibition of IL-6 signaling in dendritic cells led to a significant depletion of the Th17 population without similar effects on other T-cell subsets. These studies unveiled the possibility that Th17 cells are involved in the pathogenesis of periodontitis and confirmed that IL-6 signaling is an attractive target for treatment of this disease ( 49 ).…”

Biofilm‐induced profiles of immune response gene expression by oral epithelial cells

“…Additional studies have shown that antigen‐presenting cells (eg,. macrophages, dendritic cells) challenged with P gingivalis or Prevotella spp demonstrated increases in IL‐23 within the broader repertoire of inflammatory mediator responses, and P endodontalis LPS elicited IL‐23 linked to enhanced osteoclastogenesis, the cytokine cascade of granuloma tissues and in responses of periodontal ligament cells to LPS . However, IL‐23 in responses of oral epithelial cells is sparse.…”

“…However, IL‐23 in responses of oral epithelial cells is sparse. A single report describes IL‐23 elevations in immortalized gingival keratinocytes following infection with P gingivalis . The interesting findings with this important regulatory cytokine were its elevated expression with each of the planktonic species that was decreased substantially with the combined biofilms.…”