Monoclonal antibodies against surface determinants on gametes of Plasmodium gallinaceum block transmission of malaria parasites to mosquitoes.

Monoclonal antibodies (MAb) against gametes of the chicken malaria Plasmodium gallinaceum have been derived. All reacted with the surface of extracellular gametes of the parasite in immunofluorescent antibody reactions and all agglutinated both male and female gametes. In the absence of active complement one mu isotype MAb, la 1-D5, mediated at least 95% suppression of infectivity of the parasites to Aedes aegypti mosquitoes. Individually, MAb of the gamma 1 or gamma 2a isotypes mediated only slight suppression in the absence of active complement. Certain combinations of these MAb, however, suppressed parasite infectivity by 90 to 95%. Suppression of infectivity by the MAb was shown to be mainly due to their effects on the events leading up to or including fertilization. Certain gamma 2a isotype MAb, which otherwise mediated minimal or no suppressive effect, completely abolished infectivity of the parasites if complement was present. No target antigen could be identified by immunoprecipitation of Triton X-100 extracts of surface radioiodinated zygotes or gametes of P. gallinaceum for the mu isotype MAb. All gamma isotype MAb precipitated the same three proteins of 240,000, 56,000, and 54,000 daltons under reducing conditions on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, from extracts of radioiodinated male and female gametes. These surface proteins on gametes of both sexes of P. gallinaceum thus appear to include target antigens of anti-gamete transmission blocking immunity.