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SS Twining, M Olague-Marchan, A Ayala; Evidence For An Extravascular Corneal Coagulation System . Invest. Ophthalmol. Vis. Sci. 2002;43(13):3202.
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Purpose:In the cornea, deposition of fibrin is observed in wounded normal and plasminogen deficient animals including corneas with epithelial scrape wounds. This would suggest a coagulation pathway exists in the avascular cornea. The presence and synthesis of enzymes in the intrinsic, extrinsic and common coagulation pathways were explored. Methods:Human corneas were either processed for immunohistological stidies, or their epithelia and stromas dissected for isolation of the protein and RNA using Tri Reagent. Mouse monoclonal antibodies to Factors II (prothrombin), VII, X, XI, and Tissue Factor were used for tissue localization using the Elite ABC Kit and/or Western blots of corneal extracts. Extracted RNA was amplified by RT-PCR using specific primers to each Factor. The identity of the PCR products was confirmed by cDNA sequencing. Results:Prothrombin was widely distributed throughout the cornea being found both within the epithelial, stromal and endothelial cells and associated with the stromal extracellular matrix, Decemet's membrane and Bowman's Layer. Factor X was observed more strongly in the epithelial layer and Bowman's membrane than in other parts of the cornea. Tissue factor is mainly found in the basal epithelial cells. The common pathway Factors II and X, the extrinsic pathway Factor VII and Tissue Factor, and the intrinsic pathway Factor XI were detected by Western blots in the epithelial and stromal extracts. RT-PCR of epithelial RNA revealed the presence of mRNA for Factors II, VII, X and XI. The identity of the mRNAs was confirmed by sequencing. Conclusion:The presence of the protein and mRNA for factors from the intrinsic and extrinsic coagulation pathways as well as the common pathway suggests 1) the cornea can synthesize these factors independently of the liver and 2) the release of tissue factor (Extinsic) and exposure of abnormal surfaces (Intrinsic) may occur in the cornea as mechanisms for initiation of the cleavage of fibrinogen to fibrin.
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