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Variable antigen associated with the surface of erythrocytes infected with mature stages of Plasmodium falciparum

Immune human sera were used to select a cDNA clone expressing an asexual blood-stage antigen of Plasmodium falciparum. Antibodies affinity-purified on extracts from this clone were used to characterize the antigen by immunoblotting and immunofluorescence. The antigen is present in mature-stage parasites as a high molecular weight protein of about 250 kDa and is apparently processed to smaller fragments in the merozoite. It varies in molecular weight and antibody reactivity in different isolates, and has been localized at the erythrocyte membrane by immunoelectronmicroscopy. Part of the protein is composed of exactly repeated hexapeptide units that constitute the strain-specific determinant. This molecule has similar characteristics to the strain-specific molecule believed to be responsible for cytoadherence.

The wellcome trust lecture genes for antigens of Plasmodium falciparum

Sporozoites ofP. falciparumand other Plasmodia appear to be fairly simple antigenically, in that there is a dominant antigen, the circumsporozoite (CS) protein that forms the sporozoite surface coat (Potocnjak, Yoshida, Nussenzweig & Nussensweig, 1980; Santoroet al.1983). Consequently, the CS protein and the gene encoding it have now been studied in considerable detail (Elliset al.1983; Godsonet al.1983; Ozakiet al.1983; Dameet al.1984; Eneaet al.1984). In contrast to sporozoites, the asexual blood stagesof P. falciparumare antigenically complex. Two-dimensional gel analyses of immunoprecipitated, biosynthetically labelled antigens indicate that repeated infection withP. falciparumresults in the synthesis of antibodies against a large number of distinct antigens (Perrin & Dayal, 1982; Brownet al.1981, 1983). In further contrast to the sporozoite, the asexual blood stages of differentP. falciparumisolates exhibit a high degree of antigenic heterogeneity (Brownet al.1983; Hallet al.1983; McBride, Walliker & Morgan, 1982). Much of this antigenic diversity is no doubt due to allelic differences but clonal populations of parasites may also have the capacity to undergo antigenic variation (Hommel, David & Oligino, 1983).

A cDNA clone expressing a rhoptry protein of Plasmodium falciparum

Antibodies from immune humans were used to select a cDNA clone expressing an asexual blood stage antigen of Plasmodium falciparum. The expressed fused polypeptide was used as an affinity reagent to purify human antibodies specific for the corresponding parasite antigen. Western blotting and immunoelectronmicroscopy demonstrated that the antigen was a 105 kDa protein located in the rhoptries of merozoites. The cDNA encodes the carboxy terminus of the rhoptry antigen, a sequence rich both in charged and hydroxy amino acids.