IMPACT OF ORAL IMMUNIZATION WITH ACANTHAMOEBA ANTIGENS ON PARASITE ADHESION AND CORNEAL INFECTION

PURPOSE. To determine whether oral immunization mitigates ongoing Acan thamoeba castellanii corneal infections in pigs. METHODS. Pigs were or ally immunized with aqueous Acanthamoeba antigen mixed with cholera to xin (Ac-CT) or with saline, before or after ocular infection with A. c astellanii. Mucosal secretions (i.e., tears and enteric wash) were tes ted for Acanthamoeba-specific IgA by enzyme-linked immunosorbent assay . Enteric washes were used as a source of IgA in assays measuring the binding of trophozoites to Chinese hamster corneal epithelial (CHCE) c ells. RESULTS. Pigs immunized with Ac-CT before ocular challenge with A. castellanii had significant anti-Acanthamoeba IgA antibody titers i n their tears and enteric washes and were protected against ocular inf ection. Enteric washes from orally immunized pigs inhibited trophozoit e binding to CHCE cells in vitro by more than 75%. By contrast, pigs i mmunized after corneal infections had been established displayed kerat itis of the same severity and duration as that in control pigs. Howeve r, 80% of the orally immunized animals were resistant to rechallenge w ith Acanthamoeba-laden contact lenses, whereas none of the control ani mals was resistant. CONCLUSIONS. Oral immunization with Ac-CT protects against Acanthamoeba keratitis when administered before corneal chall enge. However, delaying oral immunization until after corneal disease is established fails to mitigate keratitis. The appearance of parasite -specific tear IgA correlates with protection and may act by preventin g the parasite's binding to the corneal epithelium.