High-titer antisera production using three adjuvants and peptide conjugates derived from malarial surface antigen MSA-2.

We have identified a 51-kDa glycosylated myristoylated merozoite surface antigen as the target of a number of monoclonal antibodies that inhibit P. falciparum invasion. This antigen has been shown to exist in a limited number of strain-specific forms, but despite wide variation in the sequences of the internal repeat regions both N- and C-terminal elements of the protein are almost totally conserved. Accordingly, we prepared a large number of overlapping peptide constructs and demonstrated that one peptide, SNTFINNA (E-71), from the N-terminus and two peptides, QHG HMHGS (G-5) and NTSDSQKE (G-12), from the C-terminus were capable, when suitably conjoined to carrier protein diphtheria toxoid, of eliciting antibodies reactive with MSA-2 from diverse strains of P. falciparum. Here we compared the immunogenicity of the peptide constructs when formulated with a Freund's adjuvant, alum and algammulin. Both peptide constructs E-71 and G-5 elicit high-titer antibodies with all three adjuvants when tested by ELISA against the immunogens themselves and by Western blotting of whole parasite extracts from two distinct parasite strains.