Comparative immunogenicity of free and carrier-conjugated peptides derived from the constant regions of a polymorphic malarial surface antigen.

One peptide (L7) representing the entire constant N-terminal region, and two peptides (L5 and L6) representing the entire C-terminal constant region of the variable merozoite surface antigen MSA2, were synthesised by solid-state (tBOC) chemistry. Mice were immunised with the peptides alone and conjoined to the carrier protein diphtheria toxoid (DT) using the hetero-bifunctional reagent maleimidocaproyloxysuccinimide (MCS). Immune response was evaluated against the peptide itself by ELISA and against the intact protein MSA2 by immunoblotting and immunofluorescence assay (IFA). Whereas all peptides elicited a strong specific antipeptide response when administered as conjugates only L7 and L6 elicited an anti-peptide response in the absence of carrier. L5 and L7 conjugates elicited sera reactive with the intact MSA2, whereas only L7 elicited such specificity in the absence of carrier.