Mice immunised with synthetic peptide from N-terminal conserved region of merozoite surface antigen-2 of human malaria parasite Plasmodium falciparum can control infection induced by Plasmodium yoelii yoelii 265BY strain.

Synthetic peptides representing conserved MSA-2 sequences are being considered as a possible component of a blood stage malaria vaccine. Antibody response towards the entire N-terminal conserved region of MSA-2 and its constituent B-epitope SNTFINNA following immunisation of BALB/c and C57BL/6 mice with different peptide constructs was assessed by ELISA and immunofluorescence antibody test (IFAT). Co-linear synthesis of SNTFINNA-epitope in tandem with the entire N-terminal conserved region peptide (P23) made this construct, namely P8.P23, to be highly immunogenic in both mouse strains, with the antibody response to the SNTFINNA epitope comparable to that following tetanus toxoid protein conjugate immunisation. The antibodies raised specifically recognised the schizont stages of Plasmodium falciparum and Plasmodium yoelii. There was no protection observed upon challenge of immunised BALB/c and C57BL/6 mice with the highly lethal Plasmodium yoelii nigeriensis strain. On the contrary, BALB/c mice immunised with P8.P23 construct were able to resist blood stage infection induced by Plasmodium yoelii yoelii 265BY parasites, while animals inoculated with P23 did not control infection. Affinity purified rabbit anti-SNTFINNA IgG showed more than 60% inhibition of merozoite invasion of fresh erythrocytes in in vitro P. falciparum culture. The low prevalence of antibody response to SNTFINNA-epitope, tested in a dot-blot assay, was observed in sera of 80 individuals living in malaria endemic area in a India; the phenomenon may point out the cryptic character of epitopes residing at the N-terminal conserved region of MSA-2.