PLASMODIUM-FALCIPARUM - FURTHER CHARACTERIZATION OF A FUNCTIONALLY ACTIVE-REGION OF THE MEROZOITE INVASION LIGAND EBA-175

A 42 amino acid peptide, Pf EBA-175 (1062-1103), also called EBA-pepti de 4 of the 175-kDa Plasmodium falciparum sialic acid binding protein, a putative merozoite invasion ligand, has been shown to be a target o f parasite growth inhibitory antibodies. We expressed and purified a r ecombinant protein, NS1-Pf EBA-175 (946-1133) which included the 42 am ino acid peptide, and compared antibodies induced by immunization with the protein to antibodies raised against the 42 amino acid peptide. S era from rabbits immunized with the recombinant protein and the synthe tic peptide immunoprecipitated authentic EBA-175, and had comparable E LISA titers against peptide Pf EBA-175 (1062-1103). However, IFAT tite rs against infected erythrocytes and growth inhibitory activity were s ubstantially higher in sera from animals immunized with the 42 amino a cid synthetic peptide. Epitope mapping of the 42 amino acid peptide id entified a 19 amino acid peptide, Pf EBA-175 (1069-1087), which blocke d the ability of antibodies against the 42 amino acid peptide to (1) i mmunoprecipitate EBA-175, (2) bind to the 42 amino acid peptide in an ELISA, and (3) recognize infected parasites in an IFAT. Sera from rabb its immunized with the 19 amino acid peptide conjugated to KLH had exc ellent parasite growth inhibitory activity (at 1:5 serum dilution, 49. 9 +/- 7.4%, mean +/- SD of three separate assays), but the activity wa s lower in each of the three assays than that of sera from rabbits imm unized with the 42 amino acid peptide (67.8 +/- 24.8%). These data ind icate that the activity of antibodies raised against the linear 42 ami no acid peptide, Pf EBA-175 (1062-1103) are primarily, if not exclusiv ely, directed against 19 of the 42 amino acids, and identify this regi on of Pf EBA 175 as a target for vaccine development. (C) 1994 Academi c Press, Inc.