Abstract
C3d, a split product of C3, interacts with its receptor (CR2 or CD21) on B cells and follicular dendritic cells (FDCs) and is crucial for induction and maintenance of a normal humoral immune response. The gene fragment coding for Ross chicken C3d gene (chC3d) was cloned and expressed as a component of fusion proteins destined for its application in the vaccine study of chicken, and for in vitro experiments. Three potential vaccine construct units 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 list A contagious disease of poultry by the Office International des Epizooties (OIE). The cloned chC3d protein and different repeats of C3d-P29 proteins that contained the F gene of NDV (C3d-P29.n-F) was generated separately in Escherichia coli and CEF cells with the help of expression vectors. All recombinant proteins were analyzed by SDS-PAGE and Western blot. The result of immunogenicity detection of different numbers of repeats of C3d-P29.n-F 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.