Two immunogenic peptide conjugates derived from P. falciparum MSA2 give rise to antibodies that crossreact with a nonhomologous 195-kDa malarial protein.

Merzoite Surface Antigen 2 (MSA2) is a 51-kDa antigen from P. falciparum that has marked sequence variation between malarial strains but contains highly conserved N- and C-terminal sequences. Previously described peptide sequences from these conserved domains are capable, when coupled to the carrier protein diphtheria toxoid (DT), of raising antibodies that recognize MSA2 in a number of malarial isolates. In this study we report the existence of two peptide conjugates from the conserved C-terminus of MSA2 which, when used as immunogens, produce antibodies that react with a 195-kDa protein and give a merzoite surface pattern on immunofluorescence assay (IFA). The antisera against these peptide conjugates do not recognize MSA2; however, the 195-kDa protein, and identical surface pattern on IFA, is recognized by a monoclonal antibody (mAB) against Merzoite Surface Antigen 1 (MSA1). These two peptides, when unconjugated to DT, are nonimmunogenic, and DT alone is not capable of inducing antibodies that react with malarial proteins. The combination of the carrier and either peptide is capable, however, of raising antibodies against MSA1, despite sharing no sequence homology with this antigen. This data thus highlights the importance of protein conformation when generating antibody against carrier-peptide conjugates.