Toll-Like Receptor Expression Is Modulated During Dry Eye Conditions in vitro

Abstract

Purpose:: Dry eye is a multifactorial syndrome in which inflammation is thought to be a significant component. The human ocular surface epithelia express a number of toll-like receptors (TLRs) that stimulate the production of proinflammatory cytokines and chemokines upon activation. Here we investigated the potential role of TLRs in dry eye by studying their expression under various culture conditions reflective of a dry eye environment.

Methods:: Cell culture: Total RNA was extracted from a normal human conjunctival epithelial cell line (IOBA-NHC) that was treated with either 10ng/ml of various cytokines (n=3, IL-1α, IL-1ß, TNFα, TGFß) or various concentrations of hyperosmolar media (n=3, 400, 450, 500mOsM) or serum free media alone for 24 hours. TLR5 and TLR9 mRNA expression was determined by real-time RT-PCR. Organ culture desiccation model: Human corneas were incubated at 37^oC for 24 hours with the epithelial surface exposed or completely submerged in culture medium. The epithelium was then collected and TLR5 and TLR9 (n=3) mRNA expression was determined by real-time RT-PCR.

Results:: Cytokines IL-1α, IL-1ß, TNFα, TGFß did not significantly modulate the expression of TLR5 mRNA in conjunctival epithelial (IOBA-NHC) cells. TLR5 mRNA expression was not significantly modulated in response to hyperosmolar stress, however TLR9 mRNA was downregulated by 0.762 and 1.18 log fold in response to 400 and 450mOsM stress respectively in HCEC. TLR5 was upregulated in the dessication culture model by 1.27 log fold, whereas TLR9 was downregulated by 3.11 log fold compared to the submerged control.

Conclusions:: These data suggest a dynamic interplay of TLRs expression during dry eye conditions and that TLR5 maybe involved in production of ocular surface inflammation in severe dry eye. Studies to further investigate the role of these and other TLRs are warranted to provide a complete understanding of their involvement in the pathogenesis of dry eye.

Keywords: cornea: tears/tear film/dry eye • inflammation • cornea: clinical science