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R.L. Redfern, R.Y. Reins, A.M. McDermott; Toll–Like Receptors and Antimicrobial Peptide Expression at the Ocular Surface . Invest. Ophthalmol. Vis. Sci. 2006;47(13):4372.
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Toll–like receptors (TLR) are a family of highly conserved glycoprotein receptors that bind a variety of microbial ligands. This study examined the expression of TLRs on the human ocular surface and their functional relationship with the antimicrobial peptides, human beta defensins (hBD) and cathelicidin (LL–37).
RNA was extracted from freshly isolated human corneal epithelial cells (HCEC) scraped from cadaveric corneas (n=3), primary cultured HCEC (n=3), corneal fibroblasts (n=3), a conjunctival cell line (IOBA–NHC) (n=3), and SV40 transformed HCEC (n=3). Expression of TLR1–10 mRNA was examined by RT–PCR. Cultured SV40 HCEC (n=2) were treated with various TLR agonists or 10ng/ml IL–1beta for 24 hours and hBD–1, 2, 3 and LL–37 mRNA expression was examined by RT–PCR. To determine if antimicrobial peptides modulated TLR mRNA expression, cultured SV40 HCEC (n=3) and IOBA–NHC (n=3) cells were treated with either 3ug/ml of hBD–2, 5ug/ml of LL–37 or media alone for 24 hours and TLR1–10 mRNA was examined by RT–PCR.
TLR1, 2, 3, 6, and 9 were expressed by all corneal and conjunctival epithelial cells. TLR 4 was expressed in SV40 HCEC and IOBA–NHC but not in primary cultured HCEC and freshly isolated HCEC. TLR5 and TLR7 were expressed in all the epithelial cells with the exception of IOBA–NHC and freshly isolated HCEC respectively. Corneal fibroblasts expressed TLR1, 3, 4, 5, 7 and 9. Toll like receptor 8 was not expressed by any cells tested. TLR10 was expressed only in SV40 HCEC but this was inconsistent. TLR agonists Pam3CSK4 (TLR4) and FSL1 (TLR2, 6) up–regulated the expression of hBD–2 mRNA, while PolyI:C (TLR3) and flagellin (TLR5) up–regulated the expression of both hBD–2 and LL–37 in SV40 HCEC. All TLR agonists examined showed no effect on hBD–1 and –3 mRNA expression. LL–37 and hBD–2 reduced TLR9 expression in IOBA–NHC and SV40 HCEC.
In addition to the known role in surveillance for microbial pathogens, TLRs at the ocular surface modulate the expression of antimicrobial peptides to provide further protection to ward off microorganisms.
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