Purpose: To investigate the expression of toll-like receptors (TLRs) in healthy and active vernal keratoconjunctivitis (VKC) conjunctiva. Design: Comparative nonrandomized interventional study. Participants: Nine patients with vernal keratoconjunctivitis and 10 healthy subjects. Methods: Normal and VKC conjunctiva were evaluated for TLR-2, TLR-4, and TLR-9 mRNA and proteins by relative real-time polymerase chain reaction and immunohistochemistry. Colocalization of TLRs was further evaluated by confocal microscopy and double-labeled immunofluorescence in T cells (CD4), mast cells (AA1), and eosinophils (EG2). Main Outcome Measures: Identification of TLRs at molecular and biochemical levels and identification of inflammatory cells that coexpress these receptors. Results: Toll-like receptor 2, TLR-4, and TLR-9 were expressed in normal and VKC conjunctival epithelium and stroma, both with a more intense immunoreactivity in the stroma. In VKC tissues, TLR-4 was upregulated, TLR-9 was downregulated, and TLR-2 was slightly decreased relative to normal tissues. Toll-like receptor 4 was localized on CD4+ lymphocytes, eosinophils, and mast cells, whereas lymphocytes and eosinophils, but not mast cells, expressed TLR-9. Conclusions: Toll-like receptors are expressed in healthy and allergic conjunctiva. The upregulation or downregulation of these receptors and their presence on inflammatory cells suggest a role of TLRs in VKC.
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