Inhibitory effects of erythrocyte membrane proteins on the in vitro invasion of the human malarial parasite (Plasmodium falciparum) into its host cell.

Abstract

The intracellular development of the erythrocytic stage of the malarial parasite (merozoite) is initiated by the attachment of the parasite to the erythrocyte surface. This paper describes an assay system to investigate Plasmodium falciparum merozoite entry into the host cell and reports on three observations regarding this interaction . (a) Merozoites do not invade human erythrocytes treated with either trypsin or neuraminidase, and both enzymes partially cleave glycophorin A, the major erythrocyte surface sialoglycoprotein . (b) A membrane protein fraction containing glycophorin A will, at low concentrations, inhibit the invasion of isolated merozoites into erythrocytes ; no other fractions of membrane proteins have appreciable effects on the reinvasion . (c) Merozoites do not reinvade erythrocytes preincubated with F ab' fragments of antibody prepared against glycophorin A. Together, these three observations imply a role for glycophorin A in the attachment of the malarial parasite to the erythrocyte surface .The development of the human malarial parasite Plasmodium falciparum occurs inside the erythrocyte, where it undergoes a process known as schizogony . The mature shizont ruptures, releasing into the serum individual merozoites which are then free to reinvade other erythrocytes . The attachment of the merozoite to the erythrocyte initiates reinvasion and a second cycle of intraerythrocytic growth. Entry has been observed by interference (1) and electron microscopy (2) and is a rapid event, being complete in 1 min . Biochemical characterization of the attachment phase has proved difficult due to the inherent problems in isolating viable merozoites free from host material. Miller and colleagues (3, 4) have studied the invasion of both P. falciparum and the simian parasite Plasmodium knowlesi.They concluded from a number of investigations that both parasites recognize specific receptors on the surface of the erythrocyte, but that the receptors are different for each parasite ; only P. knowlesi parasites interact with Duffy blood groups (3), whereas P. falciparum appears to interact with a glycoprotein on the erythrocyte surface (4) . Miller et al. (4) and Butcher et al . (5) have proposed that the existence of specific receptors on the different erythrocytes and parasites could explain hostparasite restriction of invasion. Biochemical determinants of the specificity of interaction of erythrocytes with different species of parasites has been reviewed recently by Sherman (6). In this work, the attachment of merozoites to the erythrocytes was studied by investigation of the entry of isolated merozoites.

Antibodies in malarial sera to parasite antigens in the membrane of erythrocytes infected with early asexual stages of Plasmodium falciparum.

“…The antigens responsible for the E surface IF described by us may be part of the merozoite coat that is peeled off at invasion or may be released from the merozoite rhoptries (14,(42)(43)(44). Our findings further imply that they have affinity for receptor structures in the E membrane (45)(46)(47). It has recently been reported (48) that the major 195 K Mr glycoprotein found on the surface of P.…”

“…This suggests that the corresponding antigens may have an important role in the invasion process. Whether this involves the schizont burst, a recognition function necessary for merozoite attachment (45)(46)(47), or an alteration of the E membrane to facilitate merozoite penetration (49) is presently unknown. In any event, the experiments also suggest that the antibodies against these antigens may have a host protective function in malaria infection.…”

Band 3 is a host receptor binding merozoite surface protein 1 during thePlasmodium falciparuminvasion of erythrocytes

“…8). Previously, it was shown that the ChT treatment of human RBCs resulted in a 36-94% reduction in RBC invasion by P. falciparum, depending on the concentration of ChT (35)(36)(37). Band 3 (Ϫ͞Ϫ) mouse RBCs lacking both band 3 and GPA in the RBC membrane (38,39) showed a 72% reduction (P ϭ 0.277 ϫ 10 Ϫ6 ) in binding 32 Plabeled MSP1 19 as compared with untreated wild-type mouse RBCs (Fig.…”

Two alleles of the 175-kilodalton Plasmodium falciparum erythrocyte binding antigen

“…For example, EBA-175 binds human, Aotus monkey [9] and mouse erythrocytes [15] and Pifalciparum merozoites invade these cells. However, EBA-175 binds erythrocytes with modified glycophorin less efficiently [16], and these erythrocytes have reduced invasion efficiencies [8].…”

“…[alciparum merozoites is a multi-step process involving numerous ligands and receptors [1][2][3][4][5][6][7][8]. One merozoite protein involved in initial erythrocyte binding is a 175-kDa antigen, Ahhr<'l'iatio/ls: EHA-175, 175-kDa erythrocyte binding antigen; peR, polymerase chain reaction; aa, amino acid.…”