A defining feature of resident gut macrophages is their high replenishment rate from blood monocytes attributed to tonic commensal stimulation of this site. In contrast, almost all other tissues ...contain locally maintained macrophage populations, which coexist with monocyte-replenished cells at homeostasis. In this study, we identified three transcriptionally distinct mouse gut macrophage subsets that segregate based on expression of Tim-4 and CD4. Challenging current understanding, Tim-4
CD4
gut macrophages were found to be locally maintained, while Tim-4
CD4
macrophages had a slow turnover from blood monocytes; indeed, Tim-4
CD4
macrophages were the only subset with the high monocyte-replenishment rate currently attributed to gut macrophages. Moreover, all macrophage subpopulations required live microbiota to sustain their numbers, not only those derived from blood monocytes. These findings oppose the prevailing paradigm that all macrophages in the adult mouse gut rapidly turn over from monocytes in a microbiome-dependent manner; instead, these findings supplant it with a model of ontogenetic diversity where locally maintained subsets coexist with rapidly replaced monocyte-derived populations.
Hematopoietic stem cells reside in the bone marrow, where they generate the effector cells that drive immune responses. However, in response to inflammation, some hematopoietic stem and progenitor ...cells (HSPCs) are recruited to tissue sites and undergo extramedullary hematopoiesis. Contrasting with this paradigm, here we show residence and differentiation of HSPCs in healthy gingiva, a key oral barrier in the absence of overt inflammation. We initially defined a population of gingiva monocytes that could be locally maintained; we subsequently identified not only monocyte progenitors but also diverse HSPCs within the gingiva that could give rise to multiple myeloid lineages. Gingiva HSPCs possessed similar differentiation potentials, reconstitution capabilities, and heterogeneity to bone marrow HSPCs. However, gingival HSPCs responded differently to inflammatory insults, responding to oral but not systemic inflammation. Combined, we highlight a novel pathway of myeloid cell development at a healthy barrier, defining a gingiva-specific HSPC network that supports generation of a proportion of the innate immune cells that police this barrier.
γδ T cells are enriched at barrier sites such as the gut, skin, and lung, where their roles in maintaining barrier integrity are well established. However, how these cells contribute to homeostasis ...at the gingiva, a key oral barrier and site of the common chronic inflammatory disease periodontitis, has not been explored. Here we demonstrate that the gingiva is policed by γδ T cells with a T cell receptor (TCR) repertoire that diversifies during development. Gingival γδ T cells accumulated rapidly after birth in response to barrier damage, and strikingly, their absence resulted in enhanced pathology inmurine models of the oral inflammatory disease periodontitis. Alterations in bacterial communities could not account for the increased disease severity seen in γδ T cell-deficient mice. Instead, gingival γδ T cells produced the wound healing associated cytokine amphiregulin, administration of which rescued the elevated oral pathology of tcrδ
−/− mice. Collectively, our results identify γδ T cells as critical constituents of the immuno-surveillance network that safeguard gingival tissue homeostasis.
Th17 cell plasticity is crucial for development of autoinflammatory disease pathology. Periodontitis is a prevalent inflammatory disease where Th17 cells mediate key pathological roles, yet whether ...they exhibit any functional plasticity remains unexplored. We found that during periodontitis, gingival IL-17 fate-mapped T cells still predominantly produce IL-17A, with little diversification of cytokine production. However, plasticity of IL-17 fate-mapped cells did occur during periodontitis, but in the gingiva draining lymph node. Here, some Th17 cells acquired features of Tfh cells, a functional plasticity that was dependent on IL-6. Notably, Th17-to-Tfh diversification was important to limit periodontitis pathology. Preventing Th17-to-Tfh plasticity resulted in elevated periodontal bone loss that was not simply due to increased proportions of conventional Th17 cells. Instead, loss of Th17-to-Tfh cells resulted in reduced IgG levels within the oral cavity and a failure to restrict the biomass of the oral commensal community. Thus, our data identify a novel protective function for a subset of otherwise pathogenic Th17 cells during periodontitis.
Decline of cell‐mediated immunity is often attributed to decaying
T
‐cell numbers and their distribution in peripheral organs. This study examined the hypothesis that qualitative as well as ...quantitative changes contribute to the declining efficacy of
CD
8
+
T
‐cell memory. Using a model of influenza virus infection, where loss of protective
CD
8
+
T
‐cell immunity was observed 6 months postinfection, we found no decline in antigen‐specific
T
‐cell numbers or migration to the site of secondary infection. There was, however, a large reduction in antigen‐specific
CD
8
+
T
‐cell degranulation, cytokine secretion, and polyfunctionality. A profound loss of high‐avidity
T
cells over time indicated that failure to confer protective immunity resulted from the inferior functional capacity of remaining low avidity cells. These data imply that high‐avidity central memory
T
cells wane with declining antigen levels, leaving lower avidity
T
cells with reduced functional capabilities.
Decline of cell-mediated immunity is often attributed to decaying T -cell numbers and their distribution in peripheral organs. This study examined the hypothesis that qualitative as well as ...quantitative changes contribute to the declining efficacy of CD 8 super(+) T -cell memory. Using a model of influenza virus infection, where loss of protective CD 8 super(+) T -cell immunity was observed 6 months postinfection, we found no decline in antigen-specific T -cell numbers or migration to the site of secondary infection. There was, however, a large reduction in antigen-specific CD 8 super(+) T -cell degranulation, cytokine secretion, and polyfunctionality. A profound loss of high-avidity T cells over time indicated that failure to confer protective immunity resulted from the inferior functional capacity of remaining low avidity cells. These data imply that high-avidity central memory T cells wane with declining antigen levels, leaving lower avidity T cells with reduced functional capabilities.
Immuno-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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•Distinct signals shape the Th17 cell network at the oral barrier•Oral barrier Th17 cells develop independently of commensal microbe colonization•Physiologic damage through mastication promotes the generation of oral Th17 cells•Barrier damage triggers oral Th17-cell-mediated protective immunity and inflammation
The signals regulating immunity at the gingiva, a key oral barrier, remain unclear. Dutzan et al. show that oral barrier Th17 cells are induced in response to mastication rather than commensal colonization, identifying physiologic mechanical damage as a unique tissue-specific cue conditioning local immunity and inflammation at the oral barrier.
The evolution of immune blockades in tumors limits successful antitumor immunity, but the mechanisms underlying this process are not fully understood. Depletion of regulatory T cells (Treg), a T-cell ...subset that dampens excessive inflammatory and autoreactive responses, can allow activation of tumor-specific T cells. However, cancer immunotherapy studies have shown that a persistent failure of activated lymphocytes to infiltrate tumors remains a fundamental problem. In evaluating this issue, we found that despite an increase in T-cell activation and proliferation following Treg depletion, there was no significant association with tumor growth rate. In contrast, there was a highly significant association between low tumor growth rate and the extent of T-cell infiltration. Further analyses revealed a total concordance between low tumor growth rate, high T-cell infiltration, and the presence of high endothelial venules (HEV). HEV are blood vessels normally found in secondary lymphoid tissue where they are specialized for lymphocyte recruitment. Thus, our findings suggest that Treg depletion may promote HEV neogenesis, facilitating increased lymphocyte infiltration and destruction of the tumor tissue. These findings are important as they point to a hitherto unidentified role of Tregs, the manipulation of which may refine strategies for more effective cancer immunotherapy.
Abstract
At barrier sites, resident immune cell populations help to maintain tissue homeostasis and function. These cells receive and integrate key signals from the local environment including ...stromal/epithelial cells and the commensal microbiome. Studies of the skin and gastrointestinal tract have revealed the importance of these signals for the development of host immune response. However, which commensal or tissue-specific cues are important for the immune system at the oral barrier remains minimally explored. Th17 cells have been described as key mediators of immunity at the oral barrier but also essential for periodontitis, a highly prevalent inflammatory pathology that affects the gingiva. In this study we focused in the identification of the mechanisms controlling the induction and regulation of Th17 cells in the gingiva. Our data show that IL-17-producing CD4+ T cells increase with age and their accumulation at the oral barrier occurs independently of commensal colonization. Moreover, we demonstrate that IL-6 elicited by physiological mechanical damage during mastication shapes the function of T cells at the oral mucosa, promoting Th17 differentiation. Finally, we observe that long-term mechanical damage through mastication induces IL-17 mediated bone loss at the gingival barrier. Our data highlight the notion that a variety of signals may be essential to shape the immune responses at different barrier sites, and particularly at the oral cavity, unique mechanisms modulates homeostatic and also pathogenic Th17 responses.
Foxp3(+) regulatory T cells (Tregs) are often highly enriched within the tumor-infiltrating T cell pool. Using a well-characterised model of carcinogen-induced fibrosarcomas we show that the enriched ...tumor-infiltrating Treg population comprises largely of CXCR3(+) T-bet(+) 'TH1-like' Tregs which are thymus-derived Helios(+) cells. Whilst IL-2 maintains homeostatic ratios of Tregs in lymphoid organs, we found that the perturbation in Treg frequencies in tumors is IL-2 independent. Moreover, we show that the TH1 phenotype of tumor-infiltrating Tregs is dispensable for their ability to influence tumor progression. We did however find that unlike Tconvs, the majority of intra-tumoral Tregs express the activation markers CD69, CD25, ICOS, CD103 and CTLA4 and are significantly more proliferative than Tconvs. Moreover, we have found that CD69(+) Tregs are more suppressive than their CD69- counterparts. Collectively, these data indicate superior activation of Tregs in the tumor microenvironment, promoting their suppressive ability and selective proliferation at this site.
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