Host/Pathogen Interactions in Fungal Keratitis

There are multiple overlapping mechanisms for protection against corneal fungal infections. The source of infection is nearly always exogenous and due to environmental molds (e.g., Fusarium and Aspergillus) or cutaneous yeasts (e.g., Candida albicans). Therefore, intact anatomical barriers and effective tear function are crucial first lines of defense. Antimicrobial substances such as lysozyme, lactoferrin, lipocalin, and defensins which are found in tears and/or produced by corneal cells constitute an additional line of defense. Finally, the presence of fungi or fungal products at the corneal surface triggers signaling pathways within resident corneal cells that then activate direct or indirect cellular responses. These include the recruitment of neutrophils and T cells to the site of infection and activation of antifungal mechanisms. Taken as a whole, host defenses at the ocular surface provide a multilayered and overwhelmingly effective shield against fungal keratitis.