Natural infection of Plasmodium falciparum induces inhibitory antibodies against gametocyte development in human hosts.

We identified naturally induced antibodies from malaria patients in Thailand and clarified the effect of the antibodies on gametocyte development. Fifty-nine percent of the Plasmodium falciparum-infected blood samples (17 of 29) fed to female Anopheles mosquitoes showed no oocyst infection. Seventeen percent of the samples (5 of 29) distorted the morphology and hampered the maturity of the gametocytes. A possible mechanism for the gametocyte inhibitory activity was shown by the binding of the plasma antibodies to live, immature, intraerythrocytic gametocytes during the incubation period. One hundred fifty-seven proteins specific to different gametocyte stages were explored to find the targets of the antisera that bound to the live gametocytes. However, no additional gametocyte transmission-blocking vaccine candidate was detected. Therefore, the development of alternative transmission-blocking vaccines in high-transmission areas should focus on the identification of more gametocyte antigens-inducing inhibitory antibodies that reduce gametocytemia.