Identification of HLA-A2 restricted CD8+ T-lymphocyte response to Plasmodium vivax circumsporozoite protein in individuals naturally exposed to malaria
Specific CD8− T-lymphocyte (CTL) activity against Plasmodium pre-erythrocytic stages (P-ES) derived antigens is considered one of the most important mechanisms for malaria protection. Plasmodium vivax is the second most prevalent human malaria parasite species distributed worldwide. Although several CTL epitopes have been identified in Plasmodium falciparum P-ES derived antigens, none has been described for P. vivax to date. In this study, we analysed HLA-A*0201 specific CD8− T-lymphocyte responses to the P. vivax circumsporozoite (CS) protein in both malaria exposed and nonexposed populations from the Colombian Pacific Coast. First, we analysed the prevalence of HLA-A2 allele in the study populations and found that approximately 38% of the individuals expressed this molecule and that 50% of them were HLAA* 0201. We then selected, on the P. vivax CS, five peptide sequences containing the HLA-A*0201 binding motifs and used the corresponding synthetic peptides to evaluate the CD8− T-lymphocyte interferon (IFN)-γ response. Peripheral blood mononuclear cells from the HLA-A*0201 donors were in vitro stimulated with these peptides and IFN-γ production was determined by an ELISPOT assay. Specific CD8− T lymphocyte responses were detected for three peptides located in the C-terminal region of the protein. Specific responses to these peptides were also detected in several individuals expressing different HLA-A*02 subtypes. The potential of these peptides to induce specific cytolysis and that of long synthetic peptides comprising these epitopes as P. vivax malaria vaccine subunits are being studied.