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A.C. Johnson, F.P. Heinzel, E. Diaconu, Y. Sun, A.G. Hise, E. Pearlman; Activation of Toll–Like Receptor (TLR)2, TLR4, and TLR9 in the Mammalian Cornea Induces MyD88–dependent Corneal Inflammation . Invest. Ophthalmol. Vis. Sci. 2005;46(13):2638.
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Purpose: Toll Like Receptors (TLR), which recognize microbial products, have an important role in the host innate immune response. The purpose of the current study was to determine if activation of these receptors leads to development of keratitis, and to assess the role of the common adaptor molecule Myeloid Differentiation Factor–88 (MyD88). Methods: Corneal epithelium of C57BL/6, TLR2–/–, TLR9–/– and MyD88–/– mice was abraded and treated with Pam3Cys, LPS, or CpG DNA, which bind TLR2, TLR4 and TLR9, respectively, and we measured neutrophil recruitment to the corneal stroma, development of corneal haze and chemokine production. Results: Activation of TLR2 and TLR9 stimulated neutrophil recruitment to the corneal stroma of C57BL/6 mice, but not TLR2–/– or TLR9–/– mice, respectively. In marked contrast, neutrophil migration to the corneal stroma of MyD88–/– mice challenged with Pam3Cys, LPS, or CpG DNA was completely ablated. Activation of TLR2, TLR4 and TLR9 also caused a significant increase in corneal thickness and haze, indicative of disruption of corneal clarity; however, this response was ablated in MyD88–/– mice, which were not significantly different from untreated corneas. Production of CXC chemokines MIP–2 and KC, which mediate neutrophil recruitment to the corneal stroma, was elevated in the corneal epithelium and stroma of control, but not MyD88–/– mice. Conclusions: Together, these findings indicate that the corneal epithelium has functional TLR2 and TLR9, and that TLR2, TLR4 and TLR9 signal entirely through MyD88. This pathway is therefore likely to have in important role in the early events leading to microbial keratitis.
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