Fcγ receptor-mediated phagocytosis of Plasmodium falciparum-infected erythrocytes in vitro

Although convincing evidence exists for the role of immunoglobulin G (IgG) antibodies in immunity to malaria, antibody titres do not usually predict protection. In this study we have assessed the interaction between Plasmodium falciparum- infected erythrocytes (PE), opsonized with immune serum containing different amounts of IgG antibody isotypes, with either THP-1 cells, ex-vivo human monocytes or IIAI.6 transfectant cells expressing Fcgamma RIIa-Arg/Arg131 or -His/His131 allotypes. Our results show that PMA-treated THP-1 cells were capable of phagocytosing serum-opsonized PE by Fcgamma RI (CD64) and Fcgamma RIIa (CD32), acting synergistically. The known Fcgamma RIIa polymorphism motivated us to examine its influence on IgG isotype-mediated phagocytosis of opsonized PE with human monocytes and the IIAI.6 transfectant cells expressing either allelic forms. Regardless of the cell type, PE phagocytosis with Fcgamma RIIa-His/His131 was highest following opsonization with a predominantly IgG3-containing immune serum pool. In contrast, PE phagocytosis with Fcgamma RIIa-Arg/Arg131 tended to be higher with an IgG1-containing pool. These results suggest a genetically determined influence of effector cell phenotype on IgG antibody-pathogen interaction in P. falciparum malaria.