Specificities of antibodies that inhibit merozoite dispersal from malaria-infected erythrocytes

When malaria schizont-infected erythrocytes are cultured with immune serum, antibodies prevent dispersal of merozoites, resulting in the formation of immune clusters of merozoites (ICM) and inhibition of parasite growth. Antigens recognized by these antibodies were identified by probing two dimensional immunoblots of Plasmodium falciparum antigens with antibodies dissociated from immune complexes present at the surface of merozoites in ICM. Total immune serum recognized 88 of the 135 protein spots detected by colloidal gold staining, but antibodies dissociated from immune complexes recognized only 15 protein spots attributable to no more than eight distinct antigens. Antigens recognized by antibodies that inhibit merozoite dispersal include the precursor to the major merozoite surface antigens (gp195), a 126-kDa serine-repeat antigen (SERA), the 130-kDa protein that appears to bind to glycophorin (GBP130), and the approx. 45-kDa merozoite surface antigen. One other antigen (230/215-kDa doublet) was identified by using antibodies affinity purified from recombinant expression proteins. The identities of the other three antigens (150 kDa, 127 kDa and less than 30 kDa) were not determined. This approach provides a strategy for identifying epitopes accessible at the merozoite surface which may be important components of a multivalent vaccine against blood stages of P. falciparum.