MEROZOITE SURFACE PROTEIN-1 EPITOPES RECOGNIZED BY ANTIBODIES THAT INHIBIT PLASMODIUM-FALCIPARUM MEROZOITE DISPERSAL

Serum antibodies from malaria immune donors can inhibit merozoite disp ersal by forming immune complexes through surface-accessible regions o f membrane associated antigens. Such merozoite forms are referred to a s immune clusters of merozoites (ICM). Antibodies dissociated from ICM of Plasmodium falciparum identify a restricted subset of antigens, in cluding merozoite surface protein-1 (MSP-1). We performed epitope mapp ing by comparing the reactivity of whole immune sera and ICM-derived a ntibodies in immunoblotting assays, using fourteen overlapping recombi nant MSP-1 fragments, and by ELISA, using each of the 1720 octapeptide s encoded within MSP-1. Antibodies in immune sera reacted with thirtee n recombinant fragments and hundreds of octapeptides, but antibodies d erived from ICM reacted with only six recombinant fragments and twenty octapeptides. Recombinant fragment recognition by ICM-derived antibod ies was delimited to three regions 150-200 residues long, with seven o f the octapeptide epitopes also mapping to these regions. The octapept ides recognized most strongly by antibodies in whole serum corresponde d to the degenerate repeats near the N-terminus of MSP-1, however, nei ther recombinant fragments, nor octapeptides containing these degenera te repeats, were recognized by ICM-derived antibodies. Compared to rea ctions with recombinant fragments, the reactions observed with octapep tides were weak and may represent low-affinity mimetopes or cross-reac tions. Alternatively, they may represent reactions with a portion of a n epitope assembled from more than one non-contiguous peptide. These r esults suggest that ICM-derived antibodies can be used to map surface- accessible epitopes on MSP-1 and that the recombinant fragments with w hich they react are appropriate candidates for further evaluation as c omponents of a malaria vaccine. (C) 1997 Elsevier Science B.V.