Plasmodium falciparum: Analysis of the antibody specificity to the surfaceof the trophozoite-infected erythrocyte

Current opinion supports the view that immunity to the surface of the troph ozoite-infected erythrocyte (LE) is to Plasmodium falciparum erythrocyte me mbrane protein 1 (PfEMP-1). Here we provide further evidence using the muta nt cell line 1776/C10 which no longer expresses PfEMP-1 at the IF surface, due to a subtelomeric deletion in chromosome 9. We have measured antibody r eactivity to this mutant in comparison to it's intact isogenic parent line 1776, which does express PfEMP-1, using the sensitive technique of flow cyt ometry. IgG-specific antibodies (subclass IgG1) in the plasma of hyperimmun e adults, reacted to 1776 but never to the 1776/C10 mutant. Antibody subcla sses were also measured in individual plasma samples to the surface of trop hozoite-IE. Predominantly IgG1 antibodies were detected, with a few individ ual plasma having additional IgG3 antibodies. Previous studies have used th e agglutination assay to measure sere-conversion to PfEMP-1. Here we show t hat both agglutination and flow cytometric methods are comparable, suggesti ng that agglutination of trophozoite-IE is mediated by IgG antibodies. Comp arison of the isogenic cell lines 1776 and 1776/C10 differing in expression of PfEMP-1 provides further evidence that IgG antibodies, in particular of the cytophilic subclasses, mediate recognition of PfEMP-1. (C) 1999 Academ ic Press.