Role of human tear fluid in Acanthamoeba interactions with the human corneal epithelial cells

Acanthamoeba keratitis is a painful and progressive sight-threatening infection. However, the precise mechanisms associated with the pathogenesis and pathophysiology of Acanthamoeba keratitis remain incompletely understood. Using tears from healthy individuals and an Acanthamoeba keratitis patient, we demonstrated that both subjects exhibited similar levels of Acanthamoeba-specific IgA as demonstrated by Western blotting and enzyme-linked immunosorbent assays. However, normal tears were slightly more potent in reducing Acanthamoeba binding to human corneal epithelial cells, compared with tears from Acanthamoeba keratitis patient (P>0.05 using paired T-test, one-tail distribution). Neither normal tears nor Acanthamoeba keratitis tears had any protective effects on Acanthamoeba-mediated corneal epithelial cell cytotoxicity. Both lysozyme and lactoferrin which are major constituents of the tear film and possess antibacterial properties exhibited no significant effects on Acanthamoeba binding to and cytotoxicity of human corneal epithelial cells. The role of contact lens wear in Acanthamoeba keratitis is discussed further.