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Abstract
Equine fungal keratitis (EFK) is among the most frequently reported equine ocular diseases. In humans and laboratory animals, neutrophil infiltration secondary to ocular fungal infection results in the release of matrix metalloproteinases (MMP-2 and -9) that degrade the cornea and exacerbate infection. To determine the effects of these enzymes on fungal-affected tissue, their immunohistochemical expression in purulonecrotic keratitis with and without intra-lesional fungi was examined. Expression of proteins responsible for MMP release and inhibition was also evaluated. We identified MMP-2 and 9, MIP-2, and TIMP-1 and -2 in the corneal epithelium, but not the stroma of the normal corneal samples. Fungal-affected and purulonecrotic corneal samples had all proteins expressed in increased amounts in the corneal epithelium, keratocytes, inflammatory cells, and vascular endothelial cells, with greater staining intensity in purulonecrotic samples without fungi. We conclude that MMP-2 and 9 play a significant role in the pathogenesis of equine fungal keratitis.