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Mucosal immunity at barrier sites, such as the skin and gut, have been well characterized. However, immune regulation in the oral cavity is not well understood.

This study by Dutzan & Abusleme et al. focuses on TH17 immunity at the gingiva. TH17 responses are protective against oral fungal infections, however pathogenic TH17 responses are associated with bone loss and periodontitis.

There is a microbiota-independent but antigen-dependent accumulation of CD4+TH17+ cells in the gingiva with age. These IL-17-expressors are Ki67+ and dependent on epithelial IL-6.

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Interestingly, mastication and damage drives the accumulation of CD4+TH17+ cells and neutrophils in the gingiva. However, excessive accumulation of TH17+ cells and neutrophils was associated with increased bone loss.

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The gingiva represents a unique mucosal barrier where accumulation of TH17 cells is dependent on mechanical force and barrier abrasion, but not colonization with commensals.

It remains to be investigated i) whether IL-17-producing ILCs are involved in this process, ii) what antigen is required to drive this response and iii) what regulates protective verses pathogenic IL-17 responses at the oral mucosa.

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