Mice immunized with a synthetic peptide construct corresponding to an epitope present on a Plasmodium falciparum antigen are protected against Plasmodium chabaudi challenge.

Inhibitory monoclonal antibody (MoAb) 8E7/55 recognizes a parasitophorous vacuole membrane (PVM) antigen in Plasmodium falciparum. Previous studies have identified the epitope, DNNLVSGP, recognized by the MoAb. A synthetic peptide containing this sequence was synthesized and coupled to diphtheria toxoid (DT) and was found capable of generating antibodies when used as an immunogen in mice which recognize the native antigen exp-1. In this study we demonstrate the ability of the MoAb and antisera generated against the peptide construct to recognize a 54 kD PVM antigen in Plasmodium chabaudi. The P. chabaudi antigen is synthesized in trophozoites and released to the surrounding culture media outside the parasitized erythrocyte. Mice immunized with the peptide conjugate are protected when challenged with a lethal strain of P. chabaudi. Protection in the mice correlated with the antibody titre prior to challenge. If the PVM antigen from P. chabaudi is a homologue of exp-1 from P. falciparum, then these experiments may provide a guide to the antibody titres required in human trials before antibody mediated protection could be expected. The discovery that a PVM localized antigen is secreted into the surrounding in vitro culture media provides us with a valuable model system for further investigation of protein trafficking pathways in malaria-infected erythrocytes.