Model multiple antigenic and homopolymeric peptides from non-repetitive sequences of malaria merozoite proteins elicit biologically irrelevant antibodies

Abstract

Three model peptides containing B-epitopes from conserved, non-repetitive regions of the merozoite surface antigens, MSA2 and MSA1, and the erythrocyte binding protein EBP of Plasmodium falciparum were synthesised. The peptides incorporated GPG spacers and C residues at the N and C termini, and were polymerised by oxidation to form cystine bridges. Multiple copies of essentially the same peptide sequences were also synthesised on a branching lysyl matrix to form a tetrameric multiple antigen peptide. Rabbits were immunised with the polymerised and multiple antigen peptides, in alum followed by Freund's adjuvant, and the antibody responses examined by IFA and ELISA. Reproducible antibody responses were obtained against the MSA1 and EBP but not MSA2 peptides. IgG antibody levels detected by ELISA after three injections of antigen in alum, increased significantly after further immunisation in Freund's adjuvant. IgG levels were largely maintained for at least 23 weeks after the final immunisation. IgM antibodies, generally detectable only after immunisation in Freund's adjuvant, were absent 23 weeks later. Antibody titres against the native protein on fixed parasites, assayed by IFA, were three to five orders of magnitude lower than the corresponding ELISA titres against the peptides. Antibody-dependent inhibition of P. falciparum growth in vitro could not be demonstrated with the immune rabbit sera. The MSA1 and EBP peptides elicited cross-reactive antibodies. The results suggest that the selected non-repetitive sequences are conformationally constrained in the native proteins and only a small proportion of the anti-peptide antibodies bind to the native proteins. The significance of the findings for the development of peptide vaccines and the use of peptides in immunoassays is discussed.

Immunogenicity of a malaria parasite antigen displayed by Lactococcus lactis in oral immunisations

“…Antibody titres achieved by using both L. lactis display formats of MSA2 are better than those achieved by immunisation with plasmid DNA [34] or peptide-diphtheria toxoid conjugates [35] through the intramuscular and intradermal routes. Intramuscular immunisation with synthetic peptide polymers based on MSA2 B-cell epitopes elicited high-titre antibodies against the immunising peptide, which reacted only poorly with near-native MSA2 on merozoites [36]. While very high titres (10 −6 ) of antibodies reacting with near-native MSA2 is achievable in animals with recombinant MSA2 in intramuscular immunisations, this required the use of Freund's adjuvant, which is not acceptable for human use [25].…”

Polymeric Nanoparticle Based Diagnosis and Nanomedicine for Treatment and Development of Vaccines for Cerebral Malaria: A Review on Recent Advancement

“…From IFA and ELISA assay measurements, antibody responses were studied. After the final immunization, IgG levels were maintained for 23 weeks and IgM antibodies were absent after 23 weeks . To improve SPf66 immunogenicity, a MS based delivery system was made with PLGA of sub-micrometer size and administered to mice, and it showed a considerably higher immune response.…”

“…After the final immunization, IgG levels were maintained for 23 weeks and IgM antibodies were absent after 23 weeks. 203 To improve SPf66 immunogenicity, a MS based delivery system was made with PLGA of sub-micrometer size and administered to mice, and it showed a considerably higher immune response. It produced higher IgG levels in comparison with alum adsorbed SPf66.…”