Growth of Plasmodium falciparum induces stage-dependent haemichrome formation, oxidative aggregation of band 3, membrane deposition of complement andantibodies, and phagocytosis of parasitized erythrocytes

Plasmodium falciparum-parasitized erythrocytes (RBCs) are progressively tra nsformed into non-self cells, phagocytosed by human monocytes. Haemichromes , aggregated band 3 (Bd3) and membrane-bound complement fragment C3c and Ig G were assayed in serum-opsonized stage-separated parasitized RBCs, Ail par ameters progressed from control to rings to trophozoites to schizonts: haem ichromes, nil: 0.64 +/- 0.12: 5.6 +/- 1.91; 8.4 +/- 2.8 (nmol/ml membrane); Bd3, 1 +/- 0.1; 4.3 +/- 1.5; 23 +/- 5; 25 +/- 6 (percentage aggregated); C 3c, 31 +/- 11; 223 +/- 86; 446 +/- 157: 620 +/- 120 (mOD(405)/min/ml membra ne): 35 +/- 12; 65 +/- 23; 436 +/- 127; 590 +/- 196 (mOD(405)/min/ml membra ne). All increments in rings versus controls and in trophozoites versus rin gs were highly significant. Parasite development in the presence of 100 mu mol/I beta-mercaptoethanol largely reverted haemichrome formation, Bd3 aggr egation, C3c and IgG deposition and phagocytosis, Membrane proteins extract ed by detergent C12Eg were separated on Sepharose CL-6B. Haemichromes, C3c and IgG were present exclusively in the high-molecular-weight fractions tog ether with approximately 30% of Bd3, indicating the oxidative formation of immunogenic Bd3 aggregates. Immunoblots of separated membrane proteins with anti-Bd3 antibodies confirmed Bd3 aggregates that, in part, did not enter the gel. Immunoprecipitated antibodies eluted from trophozoites reacted pre ferentially with aggregated Bd3. Changes in parasitized RBC membranes and i nduction of phagocytosis were similar to oxidatively damaged, senescent or thalassaemic RBC, indicating that parasite-induced oxidative modifications of Bd3 were per se sufficient to induce and enhance phagocytosis of malaria -parasitized RBC.