Two antigens an zygotes and ookinetes of Plasmodium yoelii and Plasmodium berghei that are distinct targets of transmission-blocking immunity

We have developed transmission-blocking monoclonal antibodies (MAbs) against Plasmodium yoelii 21-kDa (Pys21) and 28-kDa (Pys25) ookinete surface proteins, These MAbs block infectivity of P. yoelii to Anopheles stephensi. One MAb, 14, cross-reacted by Western blotting with a 28-kDa surface protein (Pbs25) of P. berghei ookinetes and blocked oocyst development, as assayed by direct mosquito feeds on passively immunized P. berghei-infected mice, In total, we have identified two ookinete surface proteins in P. yoelii one of which is also present in P. berghei. The transmission-blocking activity of the anti-Pys25 MAb 4 was complete and more potent than that of the anti-Pys21 MAb 2. Moreover, Fab fragments of MAb 4 had transmission-blocking activity in mice. In comparison, Fab fragments of MAb 2 did not have detectable transmission-blocking effect, although F(ah')(2) did, Furthermore, MAb 2 and MAb 4 appeared to block the in vitro formation and development of zygotes as well.