The goals of this study were to better understand the ecology of oral subgingival communities in health and periodontitis and elucidate the relationship between inflammation and the subgingival microbiome. Accordingly, we used 454-pyrosequencing of 16S rRNA gene libraries and quantitative PCR to characterize the subgingival microbiome of 22 subjects with chronic periodontitis. Each subject was sampled at two sites with similar periodontal destruction but differing in the presence of bleeding, a clinical indicator of increased inflammation. Communities in periodontitis were also compared with those from 10 healthy individuals. In periodontitis, presence of bleeding was not associated with different a-diversity or with a distinct microbiome, however, bleeding sites showed higher total bacterial load. In contrast, communities in health and periodontitis largely differed, with higher diversity and biomass in periodontitis. Shifts in community structure from health to periodontitis resembled ecological succession, with emergence of newly dominant taxa in periodontitis without replacement of primary health-associated species. That is, periodontitis communities had higher proportions of Spirochetes, Synergistetes, Firmicutes and Chloroflexi, among other taxa, while the proportions of Actinobacteria, particularly Actinomyces, were higher in health. Total Actinomyces load, however, remained constant from health to periodontitis. Moreover, an association existed between biomass and community structure in periodontitis, with the proportion of specific taxa correlating with bacterial load. Our study provides a global-scale framework for the ecological events in subgingival communities that underline the development of periodontitis. The association, in periodontitis, between inflammation, community biomass and community structure and their role in disease progression warrant further investigation.

Leukocyte adhesion deficiency Type I (LAD-I), a disease syndrome associated with frequent microbial infections, is caused by mutations on the CD18 subunit of β2 integrins. LAD-I is invariably associated with severe periodontal bone loss, historically attributed to lack of neutrophil surveillance of the periodontal infection. Here, we challenge this dogma by showing that the cytokine IL-17 plays a major role in the oral pathology of LAD-I. Defective neutrophil recruitment in LAD-I patients, or in LFA-1 (CD11a/CD18)-deficient mice that exhibit the LAD-I periodontal phenotype, was associated with excessive production of predominantly T cell-derived IL-17 in the periodontal tissue. The pathological elevation of IL-17 in the LFA-1–deficient periodontal tissue derived also from innate lymphoid cells. Strikingly, local treatment with anti-IL-17 (or anti-IL-23) in LFA-1-deficient mice not only blocked inflammatory periodontal bone loss but also caused a reduction in the total bacterial burden, suggesting that the IL-17-driven pathogenesis of LAD-I periodontitis leads to dysbiosis. Our findings therefore support an IL-17-targeted therapy for this condition.

One Sentence Summary: Combined human and animal model studies conclusively implicate microbiota-triggered oral mucosal Th17 cells as drivers of local immunopathology and therapeutic targets in periodontitis.

Periodontal diseases usually refer to common inflammatory disorders known as gingivitis and periodontitis, which are caused by a pathogenic microbiota in the subgingival biofilm, including Porphyromonas gingivalis, Aggregatibacter actinomycetemcomitans, Tannerella forsythia and Treponema denticola that trigger innate, inflammatory, and adaptive immune responses. These processes result in the destruction of the tissues surrounding and supporting the teeth, and eventually in tissue, bone and finally, tooth loss. The innate immune response constitutes a homeostatic system, which is the first line of defense, and is able to recognize invading microorganisms as non-self, triggering immune responses to eliminate them. In addition to the innate immunity, adaptive immunity cells and characteristic cytokines have been described as important players in the periodontal disease pathogenesis scenario, with a special attention to CD4+ T-cells (T-helper cells). Interestingly, the T cell-mediated adaptive immunity development is highly dependent on innate immunity-associated antigen presenting cells, which after antigen capture undergo into a maturation process and migrate towards the lymph nodes, where they produce distinct patterns of cytokines that will contribute to the subsequent polarization and activation of specific T CD4+ lymphocytes. Skeletal homeostasis depends on a dynamic balance between the activities of the bone-forming osteoblasts (OBLs) and bone-resorbing osteoclasts (OCLs). This balance is tightly controlled by various regulatory systems, such as the endocrine system, and is influenced by the immune system, an osteoimmunological regulation depending on lymphocyte- and macrophage-derived cytokines. All these cytokines and inflammatory mediators are capable of acting alone or in concert, to stimulate periodontal breakdown and collagen destruction via tissue-derived matrix metalloproteinases, a characterization of the progression of periodontitis as a stage that presents a significantly host immune and inflammatory response to the microbial challenge that determine of susceptibility to develop the destructive/progressive periodontitis under the influence of multiple behavioral, environmental and genetic factors.

The oral mucosa is a barrier site constantly exposed to rich and diverse commensal microbial communities, yet little is known of the immune cell network maintaining immune homeostasis at this interface. We have performed a detailed characterization of the immune cell subsets of the oral cavity in a large cohort of healthy subjects. We focused our characterization on the gingival interface, a particularly vulnerable mucosal site, with thin epithelial lining and constant exposure to the tooth adherent biofilm. In health, we find a predominance of T cells, minimal B cells, a large presence of granulocytes/neutrophils, a sophisticated network of professional antigen presenting cells (APC) and a small population of innate lymphoid cells (ILC) policing the gingival barrier. We further characterize cellular subtypes in health and interrogate shifts in immune cell populations in the common oral inflammatory disease periodontitis. In disease we document an increase in neutrophils and an up-regulation of IL-17 responses. We identify the main source of IL-17 in health and periodontitis within the CD4+ T cell compartment. Collectively our studies provide a first view of the landscape of physiologic oral immunity and serve as a baseline for the characterization of local immunopathology.

The total amount of cytokine IL-17 in GCF samples and in the culture supernatants of gingival cells are significantly increased in periodontal disease.

SummaryImmuno-surveillance networks operating at barrier sites are tuned by local tissue cues to ensure effective immunity. Site-specific commensal bacteria provide key signals ensuring host defense in the skin and gut. However, how the oral microbiome and tissue-specific signals balance immunity and regulation at the gingiva, a key oral barrier, remains minimally explored. In contrast to the skin and gut, we demonstrate that gingiva-resident T helper 17 (Th17) cells developed via a commensal colonization-independent mechanism. Accumulation of Th17 cells at the gingiva was driven in response to the physiological barrier damage that occurs during mastication. Physiological mechanical damage, via induction of interleukin 6 (IL-6) from epithelial cells, tailored effector T cell function, promoting increases in gingival Th17 cell numbers. These data highlight that diverse tissue-specific mechanisms govern education of Th17 cell responses and demonstrate that mechanical damage helps define the immune tone of this important oral barrier.

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