Potential role of macrophages in experimental keratomycosis.

PURPOSE To investigate the potential role of macrophages in keratomycosis. METHODS Macrophage elimination was achieved by repeated subconjunctival injection of liposomes containing dichloromethylene diphosphonate (Cl(2)MDP-LIP) in BALB/c mice with Fusarium solani and Candida albicans keratitis, respectively. Controls received liposomes containing phosphate-buffered saline (PBS-LIP). Infected corneas were homogenized for colony counts. Immunohistochemistry was used to determine the efficiency of macrophage depletion. The cytokine production of Th1 cells, expressed by IFN-gamma and IL-12, and of Th2 cells, expressed by IL-4 and IL-10, in corneas was analyzed by enzyme-linked immunosorbent assay. Cytokine mRNA levels were detected by real-time polymerase chain reaction. Toll-like receptor 4 (TLR4) expression and mRNA levels were also examined. Immunoblotting and immunofluorescence staining were performed to evaluate the correlation between macrophages and TLR4 distribution. RESULTS Histopathologically, more severe keratomycosis developed in the mice treated with Cl(2)MDP-LIP than those treated with PBS-LIP 5 and 7 days after inoculation. In the Cl(2)MDP-LIP-treated group, little expression of macrophages could be detected in the conjunctiva and cornea. Numerous colonies were observed. There was a marked decrease of Th1 and Th2 cytokine production and mRNA expression, and TLR4 was significantly upregulated. Immunofluorescence staining demonstrated that partial F4/80(+) cells were TLR4(+). There was a positive correlation between TLR4 mRNA and IFN-gamma mRNA expression. CONCLUSIONS Local depletion of macrophages may downregulate the immune response and aggravate fungal keratitis. Macrophages appear to play an important role in host defense against corneal infection of F. solani and C. albicans.