EFFECT OF CONTEXT AND ADJUVANT ON THE IMMUNOGENICITY OF RECOMBINANT PROTEINS AND PEPTIDE CONJUGATES DERIVED FROM THE POLYMORPHIC MALARIAL SURFACE-ANTIGEN MSA2

We have identified a 51 kDa glycosylated myristylated merozoite surfac e antigen (MSA2) as the target of a number of monoclonal antibodies wh ich inhibit in vitro invasion of the human malarial parasite Plasmodiu m falciparum. 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 repent regions both N and C terminal elements of the p rotein are almost totally conserved. Accordingly, we prepared a large number of overlapping peptide constructs and demonstrated that one pep tide SNTFINNA (E71) from the N terminus and two peptides, QHGHMHGS (G5 ) and NTSDSQKE (G12) from the C terminus could, when suitably conjoine d to the carrier protein diphtheria toxoid (DT), elicit antibodies rea ctive with MSA2 from diverse strains of P. falciparum. Here we compare the immunogenicity of these peptide constructs with two recombinant p roteins containing the entire amino acid sequence of MSA2 from the FCQ -27/PNG strain (1609) and the 3D7 strain (1623). We have formulated th ese recombinant and peptide antigens with Freund's adjuvant, Alum and Algammulin. Both recombinant and peptide antigens elicit high titre an tibodies when tested by ELISA against the immunogens themselves. Altho ugh both recombinant proteins include the constant region peptide sequ ences E71, G5 and G12, the extent of ELISA cross reaction between anti body raised against recombinant and peptide antigen or antibody raised against peptide and recombinant antigen is small and sporadic, and de pends to an extent on the adjuvant employed Antisera against both reco mbinant proteins 1609 and 1623 detected either recombinant on Western blots, as well as detecting native MSA2 in whole protein extracts from both FCQ-27/PNG and 3D7 strains. Antisera against peptide construct E 71 recognized recombinant 1609 bur Mot 1623 but recognized the native MSA2 in both strains studied Antisera against peptide construct G5 sho wed a similar pattern of recognition but also detected recombinant 162 3 on Western blotting. These results emphasize the importance of conte xt and adjuvant on the ability of selected immunogenic epitopes to eli cit antibodies appropriately directed against the native antigen.