Immunogenicity of a chicken viral Newcastle disease virus F gene-C3d fusion protein containing a chicken homologue of C3d

The gene fragment coding for Arbor Acres (AA) chicken C3d gene (chC3d) was cloned and expressed as a component of fusion proteins for its potential use as a vaccine for chickens and for in vitro experiments. This fragment of complement protein C3 (C3d) has been shown to strengthen B-cell responses when complexed with antigen. Three potential vaccine constructs were engineered to contain two, four, and six copies of chC3d-P29 coding gene, which was linked to the F gene of Newcastle disease virus (NDV), an economically important pathogen of chicken that is classified as a class A contagious disease of poultry by the Office international des épizooties (OIE). The cloned chC3d protein and different repeats of C3d-P29 proteins contained in the F gene of NDV (C3d-F-P29.n) were generated separately in Escherichia coli and CEF cells with the help of expression vectors. All recombinant proteins were analyzed by SDS-PAGE and Western blotting. The results with different repeats of C3d-F-P29.n revealed that C3d-P29 could enhance immunogenicity. Six or more repeats of C3d-P29 may be necessary for efficient enhancement of antigen-specific immune responses. To date, published research into the adjuvant activities of C3d has been limited to experiments in mice, rabbits, and cattle, and adjuvant properties of C3d have not been assessed in poultry using homologous C3d in association with antigens relevant to the target species. The chicken C3d fusion proteins detailed in this study are the first reports and they provide a basis for immunization trials in chicken, studies of receptor binding and cell activation of chicken lymphocytes, and investigations of new types of vaccines, including genetic recombinant and DNA vaccines for future use against chicken pathogens.