TRANSMISSION BLOCKADE OF PLASMODIUM-FALCIPARUM MALARIA BY ANTI-PFS230-SPECIFIC ANTIBODIES IS ISOTYPE DEPENDENT

By use of the parental hybridoma cell. line 63F2A2 that produces speci fic antibodies of immunoglobulin isotype G1 (IgG1; 63F2A2.1) against P fs230, we attempted to enrich for the synthesis of the downstream swit ch variant IgG2b and IgG2a monoclonal antibodies (MAbs) of the hybrido ma cell line (63F2A2.2b and 63F2A2.2a; respectively). The parental IgG 1 did not reduce the Plasmodium falciparum transmission in a bioassay irrespective of the presence of complement. MAbs 63F2A2.2b and 63F2A2. 2a were effective in reducing the infectivity of P. falciparum parasit es to Anopheles gambiae mosquitoes in membrane-feeding experiments. A transmission reduction of 91% was accomplished by the 63F2A2.2b switch variant, and a reduction of greater than 99% was accomplished by the 63F2A2.2a switch variant, but only in the presence of active human com plement. Subsequently, the transmission-reducing effect of MAb 63F2A2. 2b or 63F2A2.2a was confirmed in vitro by the rapid lysis of newly for med macrogametes or zygotes in the presence of active complement. MAb 63F2A2.1 did not lyse the newly formed macrogametes or zygotes irrespe ctive of the presence of complement.