Memory T cell subsets in healthy gingiva and periodontitis tissues.

BACKGROUND: In the gingival sulcus, effective and balanced innate and adaptive immune responses against subgingival plaque microbiome are crucial to maintain immune homeostasis. In this study, we investigated the memory T cell subsets in healthy gingiva and periodontitis tissues. METHODS: Anatomical localization of T cells (CD3+ , CD4+ , and CD8+ ) in healthy gingiva and periodontitis tissues were examined immunohistochemically. Subsets of memory T cells from isolated gingival cells were analyzed by flow cytometry using a cocktail of monoclonal antibodies (anti-CD69, anti-CD103, anti-CD45RA, anti-CCR7, anti-CD28, and anti-CD95). Intracellular cytokine staining of interleukin (IL)-17 and interferon (IFN)-γ expression on memory T cells in periodontitis tissues was also investigated. RESULTS: We found that healthy gingiva contains two memory T cell populations; a CD69- recirculating population and a CD69+ gingiva-resident memory T cell population. CD4+ T cells with transitional memory (TTM ) phenotype (CD45RA- CCR7- CD28+ CD95+ ) constitute the major subset within these two populations. A significant increase in the proportion of CD4+ CD69+ CD103- memory T cells was observed in periodontitis tissues compared with healthy gingiva. CD4+ memory T cells from periodontitis tissues produced either IL-17 or IFN-γ whereas CD8+ memory T cells produced only IFN-γ. CONCLUSIONS: Our findings suggest that recirculating and gingiva-resident memory T cells could represent an important part of the immune surveillance network in the connective tissue, maintaining periodontal homeostasis. Imbalance of subgingival bacterial communities could damage gingival barrier allowing bacterial antigens to get access to the deeper connective tissue where they activate memory T cells leading to deleterious inflammation; a hallmark of periodontitis.