Contribution of Chinese Pekin duck complement component C3d-P29 repeats to enhancement of Th2-biased immune responses against NDV F gene induced by DNA immunization

Materials and Methods: The gene fragment coding for Chinese Pekin duck (Anas platyrhynchos) C3d gene (duC3d) was cloned and expressed as a component of fusion proteins destined for use in in vitro experiments. Two, four and six copies of CR2-binding domain duC3d-P29 were fused, respectively, to truncated Newcastle disease virus (NDV) F gene encoding soluble glycoprotein F in pcDNA3.1.All recombinant proteins were analyzed by SDS-PAGE and Western immunoblot. BALB/c mice were, respectively, immunized with recombinant plasmids, blank vector, and inactivated vaccine. Results: The result of immunogenicity detections of The IL-4 level for F-C3d-P29.6 DNA immunization approached that for the inactivated vaccine. Compared to C3d-P29.6, C3d-P29.4 enhanced F DNA immunogenicity to a lesser extent. Furthermore, C3d-P29.n fusion increased Th2-biased immune response by inducing IL-4 production. Conclusion: We demonstrated that C3d-P29 could enhance immunogenicity by directing Th1-biased to a balanced and more effective Th1/Th2 response. The expression of the duck C3d fusion proteins in this study which was the first reported, and the detections of the cytokine level for F-C3d-P29.n in DNA immunization using the BALB/c mice as the model animal, will provide the basis for immunization trials in chicken or other poultry, studies of receptor binding and cell activation of animal lymphocytes, and investigations of new types of vaccine, including genetic recombinant and DNA vaccines for the future against relevant pathogens.