Immune responses in congenic mice to multiple antigen peptides based on defined epitopes from the malaria antigen Pf332.

Repeat sequences from the Plasmodium falciparum blood stage antigen Pf332 frequently comprise the pentapeptide VTEEI, an epitope recognized by certain parasite neutralizing antibodies. This B-cell epitope was assembled in an octavalent multiple antigen peptide (MAP) system either as trimers (VTEEI)3 (MAP1) or as an integral part of a naturally occurring Pf332 undecamer repeat sequence SVTEEIAEEDK (MAP2). Characteristics of the immunogenicity of these subunit constructs were evaluated in H-2 congenic mice. MAP1 generated antibody responses in mice of the H-2d, H-2k and H-2q haplotypes, but not in H-2b or H-2s mice, whereas MAP2 only induced antibodies in mice of H-2k haplotype. When analysing T-cell responses induced by the MAP, lymph node cells from responder strains primed in vivo with MAP1 proliferated in response to restimulation with both MAP1 and the peptide (VTEEI)3. MAP2, however, did not induce a detectable T-cell proliferation. Additionally, the lack of antibody response to MAP1 in H-2b mice could be circumvented by combining the MAP1 peptide and a H-2b-restricted T-cell epitope in a diepitope MAP construct. Despite the fact that the motif VTEEI has not been identified in Pf332 sequences in the form of a trimer, MAP1 did induce Pf332 protein-reactive antibodies. Assembly of multimers of short defined epitopes in MAP constitutes an interesting approach for the design of polyvalent subunit immunogens.