Binding ofPlasmodium falciparum-infected erythrocytes to the membrane-bound form of Fractalkine/CX₃CL1

Abstract

H uman cerebral malaria is caused by excessive adherence of Plasmodium falciparum-infected erythrocytes (pRBCs) to the microvasculature of several organs, including the brain. pRBCs containing mature parasites adhere to endothelial cells (EC) lining the lumens of postcapillary vessels, and this phenomenon is known as sequestration. After sequestration, cerebral malaria develops through a complex process involving multiple events, including obstruction of the microvasculature by pRBCs (1, 2). Several host receptors, including CD36, intercellular adhesion molecule 1 (ICAM-1), chondroitin sulfate A (CSA), platelet͞endothelial cell adhesion molecule 1 (PECAM-1/CD31), vascular cell adhesion molecule 1 (VCAM-1), thrombospondin, and E-selectin, have been identified on EC as potential mediators for cytoadherence of pRBCs (3-8). Host and parasite factors are thought to participate in the pathogenesis of severe malaria, in which symptoms of cerebral malaria are the most fulminant. However, the mechanism underlying the cytoadherence of pRBCs in the pathology of severe malaria is not completely understood. It has been suggested by several investigators that other unidentified receptors that mediate the adherence of pRBCs to EC may be present (9-11).Fractalkine͞CX 3 CL1 (FKN) is a recently identified chemokine with a unique structure. The molecule possesses a single CXXXC CD at the N terminus, which precedes 17 mucin-like repeats (the central stalk region) and the transmembrane segment at the C terminus. FKN is expressed as a membrane-bound form on EC activated by proinflammatory cytokines such as tumor necrosis factor ␣, IFN-␥, and IL-1␤ (12, 13). FKN is constitutively expressed on cells in a variety of nonhematopoietic tissues, including the brain, heart, kidneys, and lungs (12). The membrane-bound form of FKN on EC mediates adherence of blood mononuclear cells with the FKN receptor (CX 3 CR-1) (14, 15). At the same time, the soluble form promotes chemotaxis of these cells to sites of acute inflammation (12, 13). Because the key cytokine produced during malaria infection induces expression of FKN on EC at sites of sequestration, it is possible that FKN contributes to disease manifestations in patients with severe malaria.Here we report that the membrane-bound form of FKN on EC can mediate cytoadherence of pRBCs.Materials and Methods P. falciparum Culture. P. falciparum was cultured in vitro as described (16). The 21 clinical isolates of P. falciparum used in this study were obtained from uncomplicated, complicated, and cerebral malaria patients at the hospital of the International Medical Center of Japan (Tokyo), Tokyo Metropolitan Komagome Hospital, and Davao Regional Hospital (Davao, The Philippines). Informed consent was obtained from each patient before the blood sampling. Peripheral blood was collected into tubes coated with EDTA and centrifuged at 1,500 rpm for 5 min at room temperature to remove the plasma. The packed cells were washed three times with RPMI 1640 (Ϫ) (RPMI medium 1640 supplemented with 24 mM NaHCO 3 ...

Altered phenotype and gene transcription in endothelial cells, induced by Plasmodium falciparum-infected red blood cells: Pathogenic or protective?

“…CX3C1 (fractalkine) has recently been implicated in mediating adhesion of PRBCs to ECs (Hatabu et al, 2003). Other adhesion receptors such as desmocollin 2 and integrin β1 were both under-expressed with PRBCs and TNF, and over-expressed with uninfected RBCs and TNF (Table 2).…”

A restricted subset ofvargenes mediates adherence ofPlasmodium falciparum-infected erythrocytes to brain endothelial cells

“…All of the HBMEC cultures and the THBMEC line were positive for the endothelial cell markers, von Willebrand Factor (VWF), and CD31. In contrast, they were mostly negative for ICAM-2, endothelialleukocyte adhesion molecule 1 (ELAM-1), vascular cell adhesion molecule 1 (VCAM-1), and the brain endothelial candidate CX3CL1/fractalkine (33) (Fig. S3).…”

“…In recombinant protein binding assays, the IT4var6 and IT4var19 parasite clones exhibited little or no adhesion to CD36 or other known host cytoadhesion receptors (Fig. 5D), including the three brain endothelial candidate receptors, ICAM-1, HABP1/gC1qR, or Fractalkine (30,32,33 (Fig. S6).…”

“…Because CD36 is weakly expressed on brain endothelium (30,31), other host receptors would likely need to act in concert with ICAM-1 to mediate cerebral binding. Other candidates, such as HABP1/ gC1qR (32) and Fractalkine (33), have been proposed as potential cerebral sequestration receptors, but attempts to link ICAM-1 binding parasites or other binding phenotypes with cerebral malaria have yielded contradictory findings (34)(35)(36)(37). In addition, a single P. falciparum genotype can encode multiple ICAM-1-binding PfEMP1 variants (38), but whether all of these are involved in cerebral homing is unknown.…”

Cerebral malaria

“…PfEMP-1 proteins have been shown to interact with a variety of surface receptors such as ICAM-1, thrombospondin, VCAM-1, PECAM-1, αvβ3 integrin, g1CR, endoglin, P-selectin, CD36 and fractalkine 118 - 121 . Expression of some of these molecules is increased after cytokine stimulation 79 .…”