Novel vaccine antigens identified by chicken monoclonal antibodies against apicomplexans

The phylum Apicomplexa comprises obligate intracellular parasites that infect vertebrates. All invasive forms of Apicomplexa possess an apical complex, a unique assembly of organelles localized to the anterior end of the parasite and involved in host cell invasion. The chicken antibodies have been demonstrated to be useful for immunochemical research and clinical applications. In contrast to mammals, chicken antibody diversity is mostly generated by somatic mechanisms. It may be possible to produce antibodies in chickens that are difficult or impossible to produce in mammals. Previously, we have developed chicken monoclonal antibodies (mAbs) raised against Eimeria acervulina (Protozoa, Apicomplexa) and demonstrated that the chicken mAb, 6D-12-G10, recognized the conoid of E. acervulina sporozoites as the apical cytoskeleton and significantly inhibited sporozoite invasions of T lymphocytes in vitro. This antigen was highly conserved among Apicomplexan parasites, including other Eimeria spp., Toxoplasma, and Neospora. In further analyses using this mAb, we identified the apical cytoskeletal antigen of Cryptosporidium parvum, a pathogen of increasing clinical significance in livestock, birds, and wildlife as well as humans. Here, we characterized this antigen in C. parvum to assess its potential as a vaccine against cryptosporidiosis. Indirect immunofluorescence demonstrated that the reactivity of 6D-12-G10 with C. parvum sporozoites was similar to those of anti-β- and anti-γ-tubulins antibodies. Immunoelectron microscopy with the 6D-12-G10 mAb detected the antigen both on the sporozoite surface and underneath the inner membrane at the apical region of zoites. The 6D-12-G10 mAb significantly inhibited in vitro host cell invasion by C. parvum. MALDI-TOF/MS and LC-MS/MS analysis of tryptic peptides revealed that the mAb 6D-12-G10 target antigen was elongation factor-1α (EF-1α). These results indicate that EF-1α plays an essential role in mediating host cell entry by the parasites and, as such, could be a candidate vaccine antigen against the apicomplexans.
 
Keywords: Eimeria, Cryptosporidium, Apical cytoskeletal antigen, Chicken monoclonal antibody, elongation factor-1α.

Abstract presented at the 3rd International Symposium on Alternatives to Antibiotics 2019.