Differential expression of toll-like receptor mRNAs in recurrent aphthous ulceration

Toll-like receptors (TLR) are membrane proteins that recognize conserved molecules derived from bacterial, viral, fungal or host tissues. They are responsible for promoting the production of cytokines and chemokines, increasing the expression of costimulatory molecules and influencing the T Helper response (Th) toward either a Th1 or Th2 profile, thereby modulating the regulatory T cell response and controlling the integrity of the epithelial barrier. The key factors responsible for increased susceptibility to recurrent aphthous ulceration (RAU) are unclear, and because TLRs are involved in both immune regulation and control of the epithelial barrier, a deficiency in TLR activity is likely to cause increased susceptibility.

We investigated the gene expression of TLRs one through 10 in tissue samples and peripheral blood mononuclear cells (PBMC) of RAU patients in comparison to healthy controls using real-time quantitative reverse transcription PCR.

The analysis of mRNA expression levels in oral lesion showed significant (P < 0.01) overexpression of the TLR2 (~6-fold) gene and decreased expression of the TLR3 (~5-fold) and TLR5 (~6-fold) genes in comparison with healthy oral mucosa. The analysis of mRNA expression in PBMC indicated a down-regulation of TLR5 gene expression in the cells from RAU patients (P < 0.05; ~2-fold).

Our results support the hypothesis that a subset of RAU patients has fewer TLR expression that have been tentatively implicated in anti-inflammatory effects. This derangement of TLR gene expression may cause an overlay exuberant inflammation reaction in situations where normal individuals are resistant.