CHARACTERIZATION OF THE MODES OF ACTION OF ANTI-PBS21 MALARIA TRANSMISSION-BLOCKING IMMUNITY - OOKINETE TO OOCYST DIFFERENTIATION IN-VIVO

The impact of immune sera, and peripheral blood cells (PBC) from mice immunized with Plasmodium berghei ookinetes; and of purified immunoglo bulin or Fab fragments from anti-Pbs21 monoclonal antibody 13.1, upon establishment of oocyst infections in the mosquito was studied. Infect ions were initiated either from gametocyte-infected mice, or membrane feeders which contained either gametocytes or mature ookinetes. PBC fr om ookinete-immunized mice presented with non-immune serum failed to s how any transmission-blocking activity. Anti-ookinete serum, intact an ti-Pbs21 monoclonal antibody 13.1 or its Fab fragments, all inhibited oocyst formation significantly. When gametocyte-infected mice or gamet ocytes in membrane feeds were used, inhibition did not directly correl ate with antibody concentration. In membrane feeders that contained oo kinetes and antibody, concentration-dependent inhibition usually occur red. The efficacy of purified 13.1 IgG was dependent upon the ookinete concentration. The ookinete plasmalemma and cytoplasm were significan tly disturbed after 12 h in bloodmeals that contained antibody 13.1, b ut not in the isotype controls. These changes may have caused the obse rved failure of the ookinete to migrate as rapidly as the controls fro m the destructive environment of the bloodmeal.