A two fusion partner system for raising antibodies against small immunogens expressed in bacteria

Production of antisera against proteins that are not amenable to easy purification is most efficiently achieved by expressing the protein as a fusion product in bacteria. However, smaller polypeptides may present difficulties, since the majority of the antibodies may be directed against the fusion partner if the whole fusion protein is used as immunogen, while the target peptide alone may be a poor immunogen due to its small size. We have circumvented this problem through the use of two different fusion partners. The first fusion protein is used for priming the immune response and the first boost, while another fusion partner is substituted for the second boost. Five different polypeptides derived from the human polyomavirus BK, ranging in molecular weight from 4400 (39 amino acid residues) to 11,500 (96 amino acid residues), were used to test this approach. The results obtained indicate that this procedure may be very useful in raising antibodies against small antigens.