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K. R. Gornik, P. A. Moore, M. D. Figueriedo, M. L. Vandenplas; Expression of Toll-Like Receptors 2, 3, 4, 6, 9, and MD-2 in the Normal Equine Cornea, Limbus, and Conjunctiva. Invest. Ophthalmol. Vis. Sci. 2009;50(13):5544.
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TLRs 1-10 are detectable in human corneas with TLRs 1, 2, 3, 4, 6, and 9 having the highest rate of expression in healthy corneas. TLR2 and TLR4 are the major sentinel corneal receptors, recognizing PAMPs associated with fungal invasion in humans. Normal human conjunctiva contains measurable levels of TLRs 2, 4, and 9 and sclera expresses TLR4. Our study’s purpose was to determine the expression of TLRs 2, 3, 4, 6, 9, and MD-2 in the normal equine cornea, conjunctiva, and limbus tissue.
Corneal, limbal, and conjunctival tissues were collected from seven euthanized horses without evidence of ocular disease by biomicroscopy and direct ophthalmoscopy. The tissue was stored at -80°C until processing. RNA extraction with DNase-1 digestion was performed followed by RT-PCR to determine expression of TLRs 2, 3, 4, 6, 9, and MD-2. The products were resolved by electrophoresis on 1.5% agarose gels and visualized using ethidium bromide staining.
TLRs 2, 3, 4, 6, 9, and MD-2 were expressed in the cornea, limbus, and conjunctiva of seven horses. TLR3 expression was not detected in the dorsal and ventral conjunctiva of one horse.
Confirming the expression of TLRs in normal equine ocular tissues is an initial step in identifying their role in infectious keratitis, particularly fungal. The results further support the use of the horse as a model for human fungal keratitis. Studies of the TLR expression together with their cytokine profile induced during equine fungal keratitis may help further clarify the pathogenesis of the disease.
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