Characterization of a modified red cell membrane protein expressed on erythrocytes infected with the human malaria parasite Plasmodium falciparum: possible role as a cytoadherent mediating protein.

Abstract

Abstract. Infections with the human malaria Plasmodium falciparum are characterized by the retention of parasitized erythrocytes in tissue capillaries and venules. Erythrocytes containing trophozoites and schizonts attach to the endothelial cells that line these vessels by means of structurally identifiable excrescences present on the surface of the infected cell. Such excrescences, commonly called knobs, are visible by means of scanning or transmission electron microscopy. The biochemical mechanisms responsible for erythrocyte adherence to the endothelial cell are still undefined. In an attempt to identify the cytoadhesive molecule on the surface of the infected cell, we have prepared monoclonal antibodies to knob-bearing erythrocytes infected with the FCR-3 strain of P.falciparum. One of these monoclonal antibodies, designed 4A3, is an IgM that reacts (by means of immunofluorescence) with the surface of unfixed erythrocytes bearing mature parasites of the knobby line; it does not react with knobless lines or uninfected erythrocytes. By immunoelectron microscopy the monoclonal antibody 4A3 was localized to the knob region. In an in vitro cytoadherence assay, the monoclonal antibody partially blocked the binding of knob-bearing cells (FCR-3 strain) to formalin-fixed amelanotic melanoma cells. The monoclonal antibody was used to immunoprecipitate a protein from extracts of knobby erythrocytes that had been previously surface iodinated. By a two-dimensional peptide mapping technique, the antigen recognized by the monoclonal antibody was found to be structurally related to band 3 protein, the human erythrocyte anion transporter.

Synthetic peptides based on motifs present in human band 3 protein inhibit cytoadherence/sequestration of the malaria parasite Plasmodium falciparum.

“…Earlier work (5)(6)(7) indicated that infection of erythrocytes by the malaria parasite P. falciparum leads to truncated forms ofband 3 protein in the erythrocyte membrane and that these were involved in the cytoadherent behavior of the infected erythrocyte. Further, several monoclonal antibodies directed against exofacial loops 3 and 7 of band 3 protein blocked cytoadherence (I.C.…”

Increase of a Calcium Independent Transglutaminase Activity in the Erythrocyte during the Infection with Plasmodium falciparum

“…It does not seem at first sight advantageous for the parasite to enhance the fragility of its host cell. However, some of the products of transglutamination could be involved in the sequestration of the mature trophozoite in the capillary vessels (Winograd & Sherman 1989). Moreover, the rigidity of the cell and the changes in its shape could be related to the final disruption for the liberation of the merozoites.…”

“…This fact suggests the involvement of a transglutaminase activity, which causes extensive crosslinking of the cytoskeletal proteins during the maturation of the parasite. Moreover, a crosslinked form of band 3 has been shown to be an important antigen, probably related to the cytoadherence, in the mature parasite (Winograd & Sherman 1989).…”

Identification of Novel Membrane Structures in Plasmodium falciparum Infected Erythrocytes

“…Fluorescence microscopy -Freshly isolated membranous structures were processed for immunofluorescence microscopy as previously described (Winograd & Sherman 1989). Rabbit anti-erythroid spectrin was kindly provided by Dr M Wasserman, and monoclonal antibody 8E7/55 against the parasitophorous vacuolar antigen QF116 was a kind gift from Dr AR Hibbs.…”

“…Membranous structures were then processed either for transmission (Winograd & Sherman 1989) or scanning electron microscopy (SEM) (Gruenberg et al 1983) and observations were either carried out on a Phillips transmission electron microscope Model CM10 or a Phillips scanning electron microscope Model 515.…”