Local And Systemic Humoral Immune Response During Acute And Chronic Acanthamoeba keratitis in Rabbits

Abstract

Abstract: : Purpose: to study the local and systemic antibody response during the course of acute and chronic Acanthamoeba keratitis in a rabbit model. Methods: Acanthamoeba trophozoites (1x10₆/ml PBS) were injected in the corneal stroma of rabbits with prior oral immunization with aqueous Acanthamoeba antigen and others in whom Langerhans cells (LC) were recruited in the central cornea. Control groups comprised animals infected intrastromally with the same concentration of live and heat-killed parasites as well as sterile PBS. The severity score of keratitis was studied during the course of acute and chronic disease. Anti-Acanthamoeba IgA and IgG in tears and sera of these animals were determined by indirect fluorescent antibody test (IFAT) before and at different time points of infection. Evaluation of role of mucosal IgA prepared from immune and preimmune rabbit intestinal flushes in protecting against Acanthamoeba keratitis was evaluated. Results: The course of Acanthamoeba keratitis was significantly milder in animals infected after oral immunization and LC recruitment in the central cornea with a better prognosis than in infected naïve animals. Animals infected with heat- killed parasites had significantly lower severity score than those infected with live parasites (P<0.001) at different time points of infection. Tear IgA was significantly higher in animals with prior LC recruitment than infected naïve animals as well as those injected with heat- killed parasites. Mucosal IgA from intestinal flushes was found to significantly bind and agglutinate Acanthamoeba. It also inhibited Aacnthamoeba binding to rabbit corneal epithelium in vitro as well as in vivo. Conclusion: Oral immunization with aqueous Acanthamoeba antigen, and hence parasite-specific IgA in tears, as well as LC recruitment in the central cornea had a profound protective effect on the course of Acanthamoeba keratitis even after the parasites reach the stroma. The degree of overlap between their protective roles needs further elucidation.

Keywords: 302 Acanthamoeba • 449 keratitis • 469 microbial pathogenesis: experimental studies