Salivary Lymphocyte Phenotypes Differ from Blood and Serve as a Model for Other Mucosal Fluids

The oral cavity is part of the mucosal immune system of the body, embracing all mucosae including lungs, gut and nose. The oral mucosa is the gateway for a plethora of gastrointestinal and respiratory antigens and is capable of mounting a very strong mucosal immune response. Mucosal immunity is structurally and functionally similar in all mucosae and, soluble mediators including cytokines, chemokines, immunoglobulins and other proteins have been well studied in many diseases. However, the roles of mucosal immune cell phenotypes remain less studied causing setbacks in our understanding of the disease pathogeneses.

We have reviewed the importance of immune phenotyping of the cells in mucosal secretions and the employment of flow cytometry as a reliable tool for this purpose. We previously showed that CD3, CD4, CD8, Th1, and Th2 cells can be detected in stimulated whole mouth fluid (SWMF) in a reproducible and consistent manner, and their ratios may differ from those in the peripheral circulation. We now show for the first time that other salivary lymphocytes Th17, Th22, Tfh, Tregs, NKT, NK, ILC1, ILC2, and ILC3 cells can also be detected and quantified using flow cytometry. PBMC and SWMF from 119 participants were tested by flow cytometry.

Mean frequencies of all the immune cells were detected in a reproducible and consistent manner. In the SWMF the mean frequencies of Th17, Th22, Tfh and NK cells were greater than PBMC. These phenotypes in SWMF showed a negative correlation with PBMC suggesting mucosal origin and specificity.

Our findings strongly suggest that flow cytometry can be employed to detect a wide range of lymphocyte phenotypes in SWMF, a hypotonic secretion. Due to the similarities among the various mucosal secretions, this technique could be explored as a promising tool for understanding immunopathogenesis of infectious and non-infectious diseases using mucosal secretions.