Analysis of immune responses against T- and B-cell epitopes from Plasmodium falciparum liver-stage antigen 1 in rodent malaria models and malaria-exposed human subjects in India

Liver-stage antigen 1 (LSA-1) is a potential vaccine candidate against pree rythrocytic stages of malaria. We report here the immunogenicity of linear synthetic constructs delineated as T-H-cell determinants from the nonrepeat regions of Plasmodiumfalciparum LSA-1 in murine models and human subjects from areas where malaria is endemic in Rajasthan State, India. Seven peptid e constructs (LS1.1 to LS1.7) corresponding to predicted T-cell sites from both the N- and C-terminal regions and peptide LS1R from a repeat region of PfLSA-1 were synthesized to analyze the cellular immune responses. These l inear peptides were also tested for humoral responses in order to determine if there were any overlapping II-cell epitopes in the predicted T-cell sit es. Most peptides induced cellular responses in peptide-immunized BALB/c an d C57BL/6 mice as measured by proliferation and cytokine analysis. Cross-re active T-cell recognition of P. falciparam-based peptides in Plasmodium ber ghei-immune animals was evaluated, but only one peptide, LS1.2 (amino acids 1742 to 1760) triggered T-cell proliferation and interleukin-2 and gamma i nterferon secretion in P. berghei-immune splenocytes of BALB/c and C57BL/6 mice as well as in Thamnomys gazellae (natural host of P. berghei ANKA). In an enzyme-linked immunosorbent assay with the peptides, only one peptide, LS1.1, was recognized by anti-P. berghei liver-stage serum. Three peptides (LS1.1, LS1.2, and LS1.3) of the eight peptides tested in this study were r ecognized by a relatively large percentage of P. falciparum-exposed human s ubjects; the reactivities ranged from similar to 45% for LS1.3 to similar t o 60% for LS1.1 and LS1.2. Interestingly, all of the eight putative T-cell determinants were also recognized by the sera collected from malaria patien ts, although the response was variable in nature. These T-H- and B-cell epi topes may be of potential value for preerythrocytic antigen-based malaria s ubunit vaccine formulations.