Synergy between TLR-2 and TLR-3 signaling in primary human nasal epithelial cells

Although we have a detailed understanding of how single microbial derived triggers activate specialized Toll-like receptors (TLR) on airway epithelial cells, we know little of how these receptors react in a more complex environment. In everyday life, nasal epithelial cells are exposed to multiple TLR agonists, therefore we explored whether exposure to one trigger could affect the responsiveness to another TLR trigger.

Primary nasal epithelium from healthy individuals and the bronchial epithelium cell line NCI-H292 were exposed in vitro to different TLR specific agonists. The effect on the expression of different TLRs was determined using the q-PCR. We also evaluated the effect of TLR-3 stimulation on TLR-2, functionally using ELISA to determine levels of secreted mediators.

Stimulation of airway epithelial cells with a specific TLR agonist affects gene expression of other TLRs. In primary nasal epithelium, poly(I:C) challenge results in an up-regulation of the TLR-1, TLR-2, and TLR-3 genes and reduction of expression of TLR-5. Poly(I:C) induced activation of TLR-2 contributes to stronger cell responses to a TLR-2 agonist and regulation of these synergistic responses may take place at the mRNA level of IL-6 and IL-8. The effect of TLR-3 stimulation on TLR-2 functionality and most of the effects on the expression of other TLRs could be replicated in NCI-H292. Poly(I:C) failed to up-regulate TLR-1 and showed an additional up-regulation of TLR-4.

Our data suggest that to better understand TLR mediated innate responses we need to consider the impact of the presence of multiple triggers.