Characterization of the Human Immune Cell Network in Gingival Tissues

Objectives: 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. The objective of this study is to characterize the immune cell subsets of the oral cavity at steady state. We focused our characterization on the gingival interface, a particularly vulnerable mucosal site, with thinned epithelial lining and constant exposure to the tooth adherent biofilm
Methods: Human oral tissues were collected from systemically healthy subjects (n= 50 gingival and 10 mucosal biopsies) without any evidence of periodontitis, gingivitis or mucosal lesions. As a proof of principal for the evaluation of shifts in immune cell populations in disease, 6 biopsies from severe periodontitis patients were included. Tissues were digested and single cell suspensions were processed for multicolour (10-15 colour) flow cytometry, allowing an in-depth evaluation of antigen presenting cell populations (APC), T cell subpopulations, innate lymphoid cells (ILC) and cytokine production
Results: In health, we find a predominance of T cells, a large presence of granulocytes/neutrophils, a sophisticated network of professional antigen presenting cells (APC) and a small population of innate lymphoid cells policing the gingival barrier. Our analysis of cellular subtypes reveal that the majority of T cells are CD4⁺ memory resident T cells, the majority of APC are CD14⁺ and the predominant ILC type is ILC1. In disease we document an increase in neutrophils and an up-regulation of IL-17 responses, particularly within the CD4⁺ T cell compartment
Conclusions: 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