Characterization of antigens on mosquito midgut stages of Plasmodium gallinaceum. I. Zygote surface antigens.

We have defined the surface protein antigens on Plasmodium gallinaceum zygotes using radioiodination methods and rabbit anti-zygote serum which blocks transmission of the parasite to Aedes aegypti mosquitoes. Fifteen protein bands (1-15) in the molecular weight range of 40 000-240 000 and one band at the bromophenol blue dye marker were labelled by the lactoperoxidase and IODOGEN (1,3,4,6-tetrachloro-3 alpha,6 alpha-diphenylglycoluril) methods. The localization of these radioiodinated components on the cell surface was confirmed in two ways: (1) They were completely degraded by trypsin or Streptomyces griseus protease treatment of intact viable zygotes. (2) They were immunoprecipitated following incubation of intact zygotes with antibody prior to detergent solubilization. Reactivity with immune rabbit serum demonstrated that the major surface immunogens were components with Mr 240 000, 200 000, 180 000, 80 000, 55 000, 50 000 and the band at the dye marker. A band of Mr 180 000 was shown immunologically to be a host serum protein selectively adsorbed to the zygote surface. The identity of this protein and the significance of its adsorption to the surface of the zygote are unknown.