Ookinete antigens of Plasmodium berghei. Appearance on the zygote surface of an Mr 21 kD determinant identified by transmission‐blocking monoclonal antibodies

Abstract

Summary Zygotes and ookinetes of the rodent malaria Plasmodium berghei can be enriched 50-fold, from whole blood cultures by ammonium chloride lysis. Three monoclonal antibodies (MoAbs) raised against such enriched preparations specifically bind to a determinant of M_r 21 kD as assessed by ¹²⁵I-labelled goal anti-mouse IgG probed immunoblots of Western transfers of SDS-PAGE gels. Indirect immunofluorescence indicates that the 21 kD determinant bound by specific MoAbs. whilst not detectable on gametocytes or gametes, appears on the parasite surface within 2 h of exflagellation/fertilization and increases thereafler. The three MoAbs specifically binding the 21 kD determinanl block oocys! development in mosquitoes by at least 90%, as assessed either by in-vitro membrane feeds or by live feeds on passively immunized mice. These MoAbs reduce ookinete formation in vitro by between 52 and 100%. Possible mechanisms of action of these MoAbs are discussed.