The role of macrophages in Acanthamoeba keratitis.

PURPOSE Macrophages are thought to be the first line of defense in many infectious diseases and are present in high numbers in corneas with Acanthamoeba keratitis. Conjunctival macrophage depletion was performed in an animal model of Acanthamoeba infection to determine the importance of macrophages in this disease. METHODS Selective elimination of macrophages was achieved by repeated subconjunctival injection of liposomes containing dichloromethylene diphosphonate in a Chinese hamster model of Acanthamoeba keratitis. RESULTS Macrophage depletion affected the incidence, severity, and chronicity of keratitis. The incidence of infection in normal animals was approximately 60% but rose to 100% on day 4 in animals treated with liposomes containing dichloromethylene diphosphonate (C12MDP-LIP). Moreover, the clinical appearance of the keratitis in the C12MDP-LIP group was much more severe than in animals treated with liposomes containing phosphate-buffered saline at all time points. There was also a major change in the chronicity of keratitis, with an earlier onset and a prolonged and chronic course in the C12MDP-LIP treated hamsters. CONCLUSIONS The profound exacerbation of Acanthamoeba keratitis in hamsters treated with C12MDP-LIP strongly suggests that macrophages play an important role in corneal infection with Acanthamoeba trophozoites, probably by acting as a first line of defense and eliminating significant numbers of Acanthamoeba trophozoites.