Characterization by anti-Ig monoclonal antibodies of protective and non-protective antibodies against asexual forms of Plasmodium falciparum in the Saimiri monkey.

Four monoclonal antibodies (mAb) which recognize distinct epitopes on Saimiri immunoglobulins were successfully used to characterize the protective and non-protective antibodies developed by this experimental host in response to infection by the human malaria parasite Plasmodium falciparum. Two of these mAb, 3F11/G10 and 3E4/H8, were IgG-specific and directed against conformationally conserved epitopes on the intact molecule. mAb 3A2/G6 and 4G3/B5 were specific for epitopes on two distinct L chain types of all Ig. Radioimmunoassay and immunoblots indicated that L-chains defined by 3A2/G6 were present in IgG molecules of type 3F11/G10, while L chains defined by 4G3/B5 were associated with IgG of type 3E4/H8. The use of these four mAb as immunoadsorbents allowed the purification of two IgG and two Ig populations. When assayed in vivo by passive transfer experiments in recipient monkeys previously infected by P. falciparum, protection could be associated with the IgG or Ig populations of type 3F11/G10-3A2/G6. In contrast, recipient animals which received the IgG type 3E4/H8 or Ig type 4G3/B5 presented rapidly evolving parasitemia similar to that in animals which received non-immune IgG or protective immune sera depleted of the above Ig or IgG fractions. The identification of protective and non-protective Ig populations will help in the evaluation of vaccine candidates against P. falciparum.