Differential ability of specific regions of Plasmodium falciparum sexual‐stage antigen, Pfs230, to induce malaria transmission‐blocking immunity

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Abstract
Antibodies raised against an Escherichia coli-produced recombinant protein encoding a 76-kDa section (region C) of malaria transmission-blocking vaccine candidate, Pfs230, have previously been shown to significantly reduce the ability of Plasmodium falciparum parasites to infect mosquitoes (71.2–89.8%). To further define the region of the Pfs230 required for transmission-blocking activity, four recombinant proteins each encoding a section of region C (Pfs230 amino acids 443–1132) were produced using the same E. coli expression system and tested for immunogenicity in mice: (i) r230/MBP.C5′ encodes the first half of region C (amino acids 443—791, six cysteines); (ii) r230/MBP.CM1 encodes only cysteine motif (CM) 1 (amino acids 583—913, eight cysteines); (iii) r230/MBP.C1.6 (amino acids 453–913, eight cysteines) also includes all of CM1; and (iv) r230/MBP.C2 encodes only CM2 (amino acids 914–1268, 11 cysteines). All the recombinant proteins induced antibodies that recognized parasite-produced Pfs230, but the titre of the Pfs230 specific-antibodies generated varied, C = C1.6 = C5′ > CM1 > CM2. Two recombinants, r230/MBP.C5′ and r230/MBP.C1.6, induced antibody titres that were equivalent to or greater than the titre generated by r230/MBP.C. However, in contrast to r230/MBP.C, none of the recombinants induced antibodies that effectively blocked parasite infectivity to mosquitoes. This suggests that the inclusion of amino acids 914–1132 is important for the production of the transmission-blocking epitope present in region C.

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