Malaria peptides expressed on the surface of infected hepatocytes: isolation, synthesis and functional analysis

Abstract

It is now clear, from the results of various experiments, that the malarial epitopes expressed on the surface of infected hepatocytes are the target of at least two effector mechanisms: (1) a cytotoxicity, restricted by the major histocompatibility complex (MHC), which involves CD8⁺ and CD4⁺ T cells: and (2) antibody-dependent, cellular cytotoxicity. Until now, Plasmodium epitopes have been characterized from known parasite proteins and it appeared important to identify 'natural' peptides. Epitopes have been investigated using two procedures for acid extraction, one for pools of livers from infected mice (P. yoelii) or cultures (P. vivax) and one for MHC-class-I molecules present in the plasma membranes of infected livers (P. yoelii), followed by fractionation using reversed-phase, high-performance, liquid chromatography (HPLC). Two new assays to estimate the potential interest of each newly isolated epitope have been developed in parallel: (1) a quantitative, HPLC-based assay of PCR products, to estimate the hepatic load of the parasite; and (2) a brefeldin-A assay to check whether a peptide is presented on the membrane of the hepatocyte. The results of in-vivo and in-vitro experiments indicate that some of the isolated peptides are the targets of cytotoxic T cells.