Incidence and Severity of Herpetic Stromal Keratitis: Impaired by the Depletion of Lymph Node Macrophages

Abstract

HSV-1 induced stromal keratitis (HSK) is an immune-mediated disease. The role of macrophages in this process is still unclear. In this study we investigated the influence of specific macrophage depletion from the spleen and the submandibular lymph nodes by dichloromethylene diphosphonate liposomes (Cl2MDP-LIP) on the course of HSV-1 keratitis. BALB/c mice were infected corneally with 105PFU of HSV-1 (KOS). Groups of mice received Cl2MDP-LIP 7 and 2 days prior to infection. Cl2MDP-LIP were given by various routes: intravenously (i.v.) for macrophage depletion in the spleen; subcutaneously for macrophage depletion in the submandibular regional lymph node (s.c.); or both i.v. and s.c. The development of HSV-1 keratitis was evaluated clinically and histologically. A standard plaque assay from the infected eyes was used to measure virus clearance. Seventy-nine percent of the HSV-1-infected control mice (n=14) developed severe stromal keratitis by day 14 p.i. The development of stromal keratitis was inhibited by Cl2MDP-LIP given s.c. (64%;n=14;P<0.05), i.v. and s.c. (50%;n=14;P<0.05), but not by i.v. treatment alone (77%;n=13). After s.c., i.v. and s.c. Cl2MDP-LIP injection, histologically the corneal stroma had a decrease in inflammatory cell infiltration by day 14 p.i. compared to the control group, and the DTH response was reduced. The healing of epithelial HSV-1 keratitis and the virus clearance were not affected significantly. These results indicate an important function of macrophages in the course of HSV-1 keratitis. Virus replication in the eye does not appear to be affected by monocytes/macrophages of lymph nodes and spleen. In contrast, the immunopathological process of stromal HSV-keratitis that results in corneal destruction is profoundly accelerated by macrophages in the lymph nodes.