Tolerogenic T cells, Th1/Th17 cytokines and TLR2/TLR4 expressing dendritic cells predominate the microenvironment within distinct oral mucosal sites.

BACKGROUND: Most local oral vaccine strategies use the sublingual region for drug application. Only little is known about the cytokine micromilieu, the nature of T cell subtypes and expression of target structures for adjuvants at different oral mucosal regions (OMR). However, targeting the optimal OMR might ensure highest efficiency of drug uptake and lowest risk for adverse effects.
METHODS: Expression of TGF-β1, IL10 as well as Th1, Th2 and Th17 cytokines and transcription factors was investigated at different OMR and skin by quantitative real-time PCR, immunohistochemistry or flow cytometry.
RESULTS: Highest number of T cells was located in vestibular/buccal region (VBR). In contrast to skin (SK), OMR T cells produced TGF-β1, IL-10, IFN-γ and IL-17. Significantly higher TGF-β1 mRNA expression in the VBR compared with the sublingual region (SLR) and skin could be detected, while equal transcripts of IL-10 and regulatory T cell-associated transcription factor FoxP3 could be demonstrated. Expression of Th17-associated IL-17A, IL-17F, IL-22 and IL-26 mRNA could be demonstrated in VBR and SLR but not in SK. Interestingly, compared to SK, significantly higher expression of TGF-β1 and IFN-γ could be detected in OMR. Moreover, expression of toll-like receptor (TLR) 2 and TLR4 was highest in VBR with significant expression on dendritic cells in OMR.
CONCLUSION: From this data, we conclude that (i) VBR and SLR represent a protolerogenic micromilieu, (ii) both regions form a Th1 cytokine-predominated microenvironment, but also express mRNA for Th17 cytokines and (iii) TLRs detectable in VBR and SLR might serve as a target structures for adjuvants.