Role of mucosal IgA in the resistance to Acanthamoeba keratitis

PURPOSE. To determine whether oral immunization with Acanthamoeba castellan ii antigens elicits mucosal antibodies of the IgA isotype and whether mucos al antibodies affect parasite adhesion to the corneal epithelium. METHODS. Chinese hamsters were immunized with 100 mu g aqueous Acanthamoeba antigen mixed with cholera toxin (Ac-CT) and subsequently challenged with parasite-laden contact lenses that were applied to abraded corneal surfaces . Tears and stool samples were examined for the presence of Acanthamoeba-sp ecific IgA antibodies by enzyme-linked immunosorbent assay (ELISA). The eff ect of mucosal antibody on trophozoite binding to corneal epithelium and vi ability of trophozoites was examined in vitro. RESULTS. Hamsters immunized orally with Ac-CT showed significantly lower in fection rates than did control groups (21.4% versus 72.6%). ELISA analysis of mucosal specimens showed the presence of parasite-specific IgA in stool samples and tears from hamsters orally immunized with Ac-CT, but not in con trol animals. In vitro assays showed that anti-Acanthamoeba IgA did not aff ect parasite viability. However, mucosal anti-Acanthamoeba IgA profoundly i nhibited (>75%) the binding of parasites to corneal epithelial cells in vit ro. CONCLUSIONS. Oral immunization with Ac-CT induces the production of parasit e-specific IgA in mucosal secretions and prevents corneal infection. Mucosa l antibody does not affect the viability of Acanthamoeba trophozoites but s eems to prevent infection by inhibiting parasite binding to the corneal epi thelium.