Role of macrophages in Acanthamoeba keratitis

Purpose. Macrophages are believed to be the first line of defence 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 diphosphate 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% in C12MDP-LIP treated animals at day four (N=24). Moreover, the clinical appearance of the keratitis in the C12MDP-LIP group was much more severe than the PBS-LIP group at all time points. There was also a major change in the chronicity of the 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 eliminate significant numbers of Acanthamoeba trophozoites.