A liver-stage-specific antigen of Plasmodium falciparum characterized by gene cloning.

The liver phase of development of malaria parasites has been studied only recently and remains poorly understood compared to the other stages such as sporozoïtes, merozoïtes and gametes. Access to liver forms of Plasmodium falciparum has been improved by the development of in vivo and in vitro propagation methods, but the yield of mature schizonts remains limited and does not allow a detailed antigenic analysis. To date, only immunofluorescence assays (IFA) have permitted a description of a species and liver-stage-specific antigen(s) (LSA; ref. 3). Monospecific antibodies to these antigens have not been obtained due either to difficulty in immunizing mice (against LSA), or to poor stability of human monoclonal antibodies. Therefore, as a means of characterizing the LSA, we used an alternative immunological approach to identify clones of the corresponding LSA genes. We describe here the isolation of a DNA sequence coding for a P. falciparum liver-stage-specific antigen composed of repeats of 17 amino-acids, which is immunogenic in man.