STUDIES ON THE IMMUNOGENICITY OF A RECOMBINANT OOKINETE SURFACE-ANTIGEN PBS21 FROM PLASMODIUM-BERGHEI EXPRESSED IN ESCHERICHIA-COLI

Plasmodium berghei ookinete surface antigen (Pbs21), was produced as a fusion product with maltose binding protein (MBP) in Escherichia coli and used to induce transmission-blocking immunity in mice. Specificit y of induced antibody was confirmed by Western blotting with native oo kinete Pbs21, and by the indirect immunofluorescent antibody test on o okinete bloodfilms. Immunized mice were infected with P. berghei and t ransmission to Anopheles stephensi mosquitoes determined by both the i ntensity and prevalence of oocyst infections. Compared with a control group immunized with MBP alone the maximum blockade of oocyst intensit y was 66% in the mice immunized with recombinant MBP-Pbs21. Over nine experiments blockade aver aged only 33%. By comparison with native Pbs 21 protein, which usually induces greater than or equal to 90% blockad e, our data suggests the recombinant protein produced in this bacteria l system is a less effective immunogen despite expressing epitopes rec ognized by known transmission-blocking monoclonal antibodies.