Epitope mapping on the ookinete surface antigen Pbs21 of Plasmodium berghei: identification of the site of binding of transmission-blocking monoclonal antibody 13.1.

The ookinete surface protein of Plasmodium berghei Pbs21 belongs to a class of sexual stage antigens able to induce in the vertebrate host a transmission-blocking immune response. The effectors of this transmission-blocking immunity are antibody molecules directed against particular protein epitopes. The anti-Pbs21 monoclonal antibody 13.1 is known to bind a linear stretch of amino acids within the primary sequence of Pbs21 and to efficiently block the development of P. berghei in the mosquito gut. To map the 13.1 epitope along the amino acid sequence of Pbs21 we assayed the ability of 13.1 antibody to recognize, in Western blot, a series of Pbs21 deletion mutants as well as the ability of synthetic peptides to inhibit 13.1 binding to full length Pbs21. The epitope was identified within the second EGF-like domain of the Pbs21 molecule.