Excessive inflammatory response to infection in experimental peri-implantitis: Resolution by Resolvin D2.

AIM: The aetiology and pathogenesis of peri-implantitis are currently under active research. This study aimed to dissect the pathogenesis of murine experimental peri-implantitis and assess Resolvin D2 (RvD2) as a new treatment modality. MATERIALS AND METHODS: Four weeks following titanium implant insertion, mice were infected with Porphyromonas gingivalis using single or multiple oral lavages. RvD2 was administrated following infection, and tissues were analysed using flow cytometry, quantitative RT-PCR, taxonomic profiling, and micro-computed tomography. RESULTS: Repeated infections with Pg resulted in microbial dysbiosis and a higher influx of innate and adaptive leukocytes to the peri-implant mucosa (PIM) than to gingiva surrounding the teeth. This was accompanied by increased expression levels of IFN-α, IL-1ß, and RANKL\OPG ratio. Interestingly, whereas repetitive infections resulted in bone loss around implants and teeth, a single infection induced bone loss only around implants, suggesting a higher susceptibility of the implants to infection. Treatment with RvD2 prevented Pg-driven bone loss and reduced leukocyte infiltration to the PIM. CONCLUSIONS: Murine dental implants are associated with dysregulated local immunity and increase susceptibility to pathogen-induced peri-implantitis. However, the disease can be prevented by RvD2 treatment, highlighting the promising therapeutic potential of this treatment modality.

Mutual interplay between IL-17-producing γδT cells and microbiota orchestrates oral mucosal homeostasis.

γδT cells are a major component of epithelial tissues and play a role in tissue homeostasis and host defense. γδT cells also reside in the gingiva, an oral tissue covered with specialized epithelium that continuously monitors the challenging dental biofilm. Whereas most research on intraepithelial γδT cells focuses on the skin and intestine epithelia, our knowledge on these cells in the gingiva is still incomplete. In this study, we demonstrate that even though the gingiva develops after birth, the majority of gingival γδT cells are fetal thymus-derived Vγ6+ cells, and to a lesser extent Vγ1+ and Vγ4+ cells. Furthermore, we show that γδT cells are motile and locate preferentially in the epithelium adjacent to the biofilm. Vγ6+ cells represent the major source of IL-17-producing cells in the gingiva. Chimeric mice and parabiosis experiments indicated that the main fraction of gingival γδT cells is radioresistant and tissue-resident, persisting locally independent of circulating γδT cells. Notably, gingival γδT cell homeostasis is regulated by the microbiota as the ratio of Vγ6+ and Vγ4+ cells was reversed in germ-free mice, and their activation state was decreased. As a consequence, conditional ablation of γδT cells results in elevated gingival inflammation and subsequent alterations of oral microbial diversity. Taken together, these findings suggest that oral mucosal homeostasis is shaped by reciprocal interplays between γδT cells and local microbiota.

GAS6 is a key homeostatic immunological regulator of host-commensal interactions in the oral mucosa.

The oral epithelium contributes to innate immunity and oral mucosal homeostasis, which is critical for preventing local inflammation and the associated adverse systemic conditions. Nevertheless, the mechanisms by which the oral epithelium maintains homeostasis are poorly understood. Here, we studied the role of growth arrest specific 6 (GAS6), a ligand of the TYRO3-AXL-MERTK (TAM) receptor family, in regulating oral mucosal homeostasis. Expression of GAS6 was restricted to the outer layers of the oral epithelium. In contrast to protein S, the other TAM ligand, which was constitutively expressed postnatally, expression of GAS6 initiated only 3-4 wk after birth. Further analysis revealed that GAS6 expression was induced by the oral microbiota in a myeloid differentiation primary response gene 88 (MyD88)-dependent fashion. Mice lacking GAS6 presented higher levels of inflammatory cytokines, elevated frequencies of neutrophils, and up-regulated activity of enzymes, generating reactive nitrogen species. We also found an imbalance in Th17/Treg ratio known to control tissue homeostasis, as Gas6-deficient dendritic cells preferentially secreted IL-6 and induced Th17 cells. As a result of this immunological shift, a significant microbial dysbiosis was observed in Gas6-/- mice, because anaerobic bacteria largely expanded by using inflammatory byproducts for anaerobic respiration. Using chimeric mice, we found a critical role for GAS6 in epithelial cells in maintaining oral homeostasis, whereas its absence in hematopoietic cells synergized the level of dysbiosis. We thus propose GAS6 as a key immunological regulator of host-commensal interactions in the oral epithelium.

[MAXILLOFACIAL TRAFFIC INJURIES RELATED TO MOTOR VEHICLE ACCIDENTS IN JERUSALEM 2000-2013: CHARACTERISTICS AND ETHNIC COMPARISONS].

BACKGROUND: The aim of this study is to review motor-vehicle accident-related maxillofacial injuries (MVA-MFI) trauma cases and to investigate whether the growing population and traffic congestion, as well as differences in driving practice, vehicle safely devices and infrastructure facilities might differentially affect the pattern of MVA-MFI among Jewish and Arab populations. METHODS: This retrospective study reviews maxillofacial injuries (MFI) identified among all trauma patients who were admitted to Hadassah Ein Kerem hospital, Jerusalem, between the years 2000 to 2013. RESULTS: Out of 29,997 trauma patients, 1,720 presented with MFI, with motor-vehicle accident (MVA) being the major cause of injury (705 patients, 41%). Their mean age was 29.9±21.0 years with a prominent male and Jewish predominance (4.3:1 and 1.8:1, respectively). Most MVA-MFI casualties were car drivers (41%), followed by pedestrians (30%). Pedestrians with MVA-MFI were mainly children and aged persons, whereas drivers were mainly adults. Males and Arabs were more likely to present with higher injury severity score (ISS). Safety belts were not used in the majority of car MVA-MFI patients (54%). Yet, the ISS score did not correlate with the use of safety devices. Mandibular fractures were the most common (21%), followed by nasal bones (20%), zygoma (17%), orbit (16%), maxilla (15%) and teeth (11%). Age was significantly associated with increased maxillary and nasal fractures and with decreased incidence of mandibular and teeth fractures. DISCUSSION: Based on our review, young males and specifically Arab patients suffered from MFI and high ISS scores as a result of MVA. The findings and their interpretations are discussed.

Maturation of the neonatal oral mucosa involves unique epithelium-microbiota interactions.

Postnatal host-microbiota interplay governs mucosal homeostasis and is considered to have life-long health consequences. The intestine monolayer epithelium is critically involved in such early-life processes; nevertheless, the role of the oral multilayer epithelium remains ill defined. We demonstrate that unlike the intestine, the neonate oral cavity is immensely colonized by the microbiota that decline to adult levels during weaning. Neutrophils are present in the oral epithelium prenatally, and exposure to the microbiota postnatally further recruits them to the preamble neonatal epithelium by γδT17 cells. These neutrophils virtually disappear during weaning as the epithelium seals. The neonate and adult epithelium display distinct turnover kinetics and transcriptomic signatures, with neonate epithelium reminiscent of the signature found in germ-free mice. Microbial reduction during weaning is mediated by the upregulation of saliva production and induction of salivary antimicrobial components by the microbiota. Collectively, unique postnatal interactions between the multilayer epithelium and microbiota shape oral homeostasis.

Niche rather than origin dysregulates mucosal Langerhans cells development in aged mice.

Unlike epidermal Langerhans cells (LCs) that originate from embryonic precursors and are self-renewed locally, mucosal LCs arise and are replaced by circulating bone marrow (BM) precursors throughout life. While the unique lifecycle of epidermal LCs is associated with an age-dependent decrease in their numbers, whether and how aging has an impact on mucosal LCs remains unclear. Focusing on gingival LCs we found that mucosal LCs are reduced with age but exhibit altered morphology with that observed in aged epidermal LCs. The reduction of gingival but not epidermal LCs in aged mice was microbiota-dependent; nevertheless, the impact of the microbiota on gingival LCs was indirect. We next compared the ability of young and aged BM precursors to differentiate to mucosal LCs. Mixed BM chimeras, as well as differentiation cultures, demonstrated that aged BM has intact if not superior capacity to differentiate into LCs than young BM. This was in line with the higher percentages of mucosal LC precursors, pre-DCs, and monocytes, detected in aged BM. These findings suggest that while aging is associated with reduced LC numbers, the niche rather than the origin controls this process in mucosal barriers.

Resolvin D2 Restrains Th1 Immunity and Prevents Alveolar Bone Loss in Murine Periodontitis.

Periodontitis is an infectious inflammatory disease of the supporting structures of the teeth. Resolvins are part of a large family of specialized pro-resolving lipid mediators that enhance active resolution of inflammation and return of inflammatory lesions to homeostasis. In this paper, we demonstrate that resolvin D2 (RvD2), a product of docosahexaenoic acid (DHA) metabolism, prevents alveolar bone loss in Porphyromonas gingivalis-induced experimental periodontitis. Investigations of the immune mechanism of RvD2 actions reveal that 6 weeks after infection, the gingiva of RvD2-treated mice exhibit decreased CD4+ T-cells as well as lower RANKL expression levels and higher osteoprotegerin expression levels. Systemically, RvD2 prevents chronic secretion of IFN-γ and rapidly restores IFN-α levels, without dampening the P. gingivalis-specific immune response. In the gingiva, immediately after P. gingivalis inoculation, RvD2 regulates the mRNA expression of IFN-γ, IL-1ß, TNF-α, and IL-10, hence contributing to maintaining local homeostasis. Moreover, RvD2 treatment reduces local neutrophil numbers, whereas pro-resolving macrophage counts were increased. These findings suggest that RvD2 resolves innate inflammatory responses, inhibiting systemic and gingival Th1-type adaptive responses that are known to mediate alveolar bone loss in this model.

Impaired Differentiation of Langerhans Cells in the Murine Oral Epithelium Adjacent to Titanium Dental Implants.

Peri-implantitis is a destructive inflammatory process affecting tissues surrounding dental implants and it is considered a new global health concern. Human studies have suggested that the frequencies of Langerhans cells (LCs), the main antigen-presenting cells (APCs) of the oral epithelium, are dysregulated around the implants. Since LCs play a role in regulating oral mucosal homeostasis, we studied the impact of dental titanium implants on LC differentiation using a novel murine model. We demonstrate that whereas the percentage of LC precursors (CD11c+MHCII+) increased in the peri-implant epithelium, the frequencies of LCs (CD11c+MHCII+EpCAM+langerin+) were significantly reduced. Instead, a population of partially developed LCs expressing CD11c+MHCII+EpCAM+ but not langerin evolved in the peri-implant mucosa, which was also accompanied by a considerable leukocyte infiltrate. In line with the increased levels of LC precursors, expression of CCL2 and CCL20, chemokines mediating their translocation to the epithelium, was elevated in the peri-implant epithelium. However, expression of TGF-ß1, the major cytokine driving final differentiation of LCs, was reduced in the epithelium. Further analysis revealed that while the expression of the TGF-ß1 canonical receptor activing-like kinase (ALK)5 was upregulated, expression of its non-canonical receptor ALK3 was decreased. Since titanium ions releasing from implants were proposed to alter APC function, we next analyzed the impact of such ions on TGF-ß1-induced LC differentiation cultures. Concurring with the in vivo studies, the presence of titanium ions resulted in the generation of partially developed LCs that express CD11c+MHCII+EpCAM+ but failed to upregulate langerin expression. Collectively, these findings suggest that titanium dental implants have the capacity to impair the development of oral LCs and might subsequently dysregulate immunity in the peri-implant mucosa.

Sequential BMP7/TGF-ß1 signaling and microbiota instruct mucosal Langerhans cell differentiation.

Mucosal Langerhans cells (LCs) originate from pre-dendritic cells and monocytes. However, the mechanisms involved in their in situ development remain unclear. Here, we demonstrate that the differentiation of murine mucosal LCs is a two-step process. In the lamina propria, signaling via BMP7-ALK3 promotes translocation of LC precursors to the epithelium. Within the epithelium, TGF-ß1 finalizes LC differentiation, and ALK5 is crucial to this process. Moreover, the local microbiota has a major impact on the development of mucosal LCs, whereas LCs in turn maintain mucosal homeostasis and prevent tissue destruction. These results reveal the differential and sequential role of TGF-ß1 and BMP7 in LC differentiation and highlight the intimate interplay of LCs with the microbiota.