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M. Garate, H. Alizadeh, S. Neelam, J. Niederkorn, N. Panjwani; Oral Immunization With Acanthamoeba Mannose–Binding Protein Provides Protection Against Amoebic Keratitis . Invest. Ophthalmol. Vis. Sci. 2004;45(13):4975.
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Purpose: The mannose–binding protein (MBP) of Acanthamoeba is thought to play a key role in the pathogenesis of Acanthamoeba keratitis by mediating the adhesion of parasites to host cells. The goal of the present study was to assess whether oral immunization with MBP provides protection against Acanthamoeba keratitis in a Chinese hamster animal model. Methods: The amoeba–MBP was isolated, its cDNA was cloned and expressed in E. coli. Chinese hamsters (N=6) were orally immunized with four weekly doses of 200 µg of recombinant MBP (rMBP) mixed with cholera toxin. Another six animals receiving phosphate–buffered saline were used as controls. After the immunization period, the corneas of hamsters were abraded and challenged with Acanthamoeba using parasite–laden contact lenses. Starting on day 5 postinfection, the infection severity was scored based on the extent of corneal neovascularization, infiltrate and ulceration. Tear samples collected once per week during the immunization period were examined for the presence of MBP–specific IgA by enzyme–linked immunosorbent assay (ELISA). For this purpose, 96–well plates were coated with 1 µg/ml rMBP and the IgA detection was performed as described by Leher et al. (Invest. Ophthalmol. Vis. Sci.  39: 2666–73). Results: Hamsters orally immunized with rMBP showed significantly milder infection compared to control groups (Mean Disease severity: 1.1 ± 0.2 versus 2.0 ± 0.3 on day 5 postinfection [P<0.05], 0.7 ± 0.05 versus 1.5 ± 0.1 on day 8 postinfection [P<0.05], for immunized and control animals respectively. ELISA analysis revealed the presence of anti–MBP IgA in tears and gut washes of hamsters orally immunized with MBP but not in control animals. Conclusions: Oral immunization with rMBP protects against Acanthamoeba keratitis when administered before corneal challenge. The appearance of MBP–specific tear IgA correlates with protection and may act by preventing the parasite's binding to the corneal epithelium. The Acanthamoeba MBP may serve as a potential immunization reagent for protection against infection in high–risk patients.
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