A new recombinant hybrid polypeptide and its immunologic adjuvant activity for inactivated infectious bursal disease vaccine.

Both bursin (Lys-His-Gly-NH2) and Gagnon's peptides (Lys-Asn-Pro-Tyr) can induce B-cell differentiation. However, it is unclear whether a recombinant hybrid polypeptide consisting of a tandem array of 14 copies of bursin and two copies of Gagnon's peptide can induce the proliferative activity of lymphocytes. Here, this recombinant hybrid polypeptide was expressed in Escherichia coli and purified by SDS-PAGE. Various assays showed that it not only promoted B-lymphocyte proliferation in vitro but also increased the titers of antibodies directed against infectious bursal disease virus fourfold in the sera of chickens vaccinated with the inactivated infectious bursal disease virus vaccine. The recombinant hybrid polypeptide also reduced the pathological lesions in the bursa of Fabricius caused by infectious bursal disease virus BC6/85. Our results show that this recombinant hybrid polypeptide may be a promising immune adjuvant.