Anthony R. Berendt

The binding site on ICAM-1 for plasmodium falciparum-infected erythrocytes overlaps, but is distinct from, the LFA-1-binding site

The intercellular adhesion molecule-1 (ICAM-1, CD54) is one of three putative endothelial receptors that mediate in vitro cytoadherence of P. falciparum-infected erythrocytes. Since cytoadherence to postcapillary venular endothelium is thought to be a major factor in the virulence of P. falciparum malaria, we have examined the interaction between ICAM-1 and the P. falciparum-infected cell, and have compared it with the interaction to the physiological counter receptor, the leukocyte integrin LFA-1. Our results demonstrate that the malaria-binding site resides in the first two domains of the ICAM-1 molecule and overlaps, but is distinct from, the LFA-1 site.

Rolling and stationary cytoadhesion of red blood cells parasitized by Plasmodium falciparum: separate roles for ICAM‐1, CD36 and thrombospondin

Summary. Adhesion of parasitized erythrocytes to microvascular endothelium is a central event in the pathogenesis of severe falciparum malaria. We have characterized the adhesion of flowing parasitized red blood cells to three of the known endothelial receptors coated on plastic surfaces (CD36, intercellular adhesion molecule‐1 (ICAM‐1) and thrombospondin (TSP)), and also to cells bearing these receptors (human umbilical vein endothelial cells (HUVEC) and platelets). All of the surfaces could mediate adhesion at wall shear stress within the physiological range. The great majority of adherent parasitized cells formed rolling rather than static attachments to HUVEC and ICAM‐1, whereas static attachments predominated for platelets, CD36 and TSP. Studies with monoclonal antibodies verified that binding the HUVEC was mainly via ICAM‐1, and to platelets via CD36. Adhesion via ICAM‐1 was least sensitive to increasing wall shear stress, but absolute efficiency of adhesion was greatest for CD36, followed by ICAM‐1, and least for TSP. TSP did not give long‐lasting adhesion under flow, whereas cells remained adherent to CD36 or ICAM‐1. We propose that the different receptors may have complementary roles in modulating adhesion in microvessels. Initial interaction at high wall shear stress may be of a rolling type, mediated by ICAM‐1 or other receptors, with immobilization and stabilization occurring via CD36 and/or TSP.

Fibronectin-binding protein A of Staphylococcus aureus has multiple, substituting, binding regions that mediate adherence to fibronectin and invasion of endothelial cells

Invasive Staphylococcus aureus infection frequently involves bacterial seeding from the bloodstream to other body tissues, a process necessarily involving interactions between circulating bacteria and vascular endothelial cells. Staphylococcus aureus fibronectin‐binding protein is central to the invasion of endothelium, fibronectin forming a bridge between bacterial fibronectin‐binding proteins and host cell receptors. To dissect further the mechanisms of invasion of endothelial cells by S. aureus, a series of truncated FnBPA proteins that lacked one or more of the A, B, C or D regions were expressed on the surface of S. aureus and tested in fibronectin adhesion, endothelial cell adhesion and invasion assays. We found that this protein has multiple, substituting, fibronectin‐binding regions, each capable of conferring both adherence to fibronectin and endothelial cells, and endothelial cell invasion. By expressing S. aureus FnBPA on the surface of the non‐invasive Gram‐positive organism Lactococcus lactis, we have found that no other bacterial factor is required for invasion. Furthermore, we have demonstrated that, as with other cell types, invasion of endothelial cells is mediated by integrin α5β1. These findings may be of relevance to the development of preventive measures against systemic infection, and bacterial spread in the bacteraemic patient.

Intercellular adhesion molecule-1 and CD36 synergize to mediate adherence of Plasmodium falciparum-infected erythrocytes to cultured human microvascular endothelial cells.

We have compared the adhesion of Plasmodium falciparum-infected erythrocytes to human dermal microvascular endothelial cells (HDMEC) and human umbilical vein endothelial cells (HUVEC) and have assessed the relative roles of the receptors CD36 and intercellular adhesion molecule-1 (ICAM-1). HUVEC (a cell line that expresses high levels of ICAM-1 but no CD36) mediate low levels of adhesion, whereas HDMEC (which constitutively express CD36) mediate high levels of adhesion even before ICAM-1 induction ICAM-1 expression leads to yet greater levels of adhesion, which are inhibited both by anti-ICAM-1 and CD36 mAbs, despite no increase in the expression of CD36. The results indicate the presence of a substantial population of infected cells that require the presence of both receptors to establish adhesion. Synergy between these receptors could be demonstrated using a number of parasite lines, but it could not be predicted from the binding of these same parasite lines to purified ICAM-1 and CD36. This phenomenon could not be reproduced using either purified receptors presented on plastic, or formalin-fixed HDMEC, suggesting that receptor mobility is important. This is the first study to demonstrate receptor synergy in malaria cytoadherence to human endothelial cells, a phenomenon necessary for parasite survival and associated with disease severity.

Sequestration in Plasmodium falciparum malaria: Sticky cells and sticky problems

Plasmodium falciparum is unique among the human malarias in displaying the phenomenon of sequestration, in which mature infected erythrocytes adhere to post-capillary and capillary venular endothelium. In this review, Tony Berendt, David Ferguson and Chris Newbold describe the molecular and cellular biology of sequestration and cytoadherence. Potential host receptors identified to date that are expressed on endothelial cells (CD36, thrombospondin and ICAM-1) and the parasite-mediated changes in the infected erythrocyte (knob formation, senescence and the expression of parasite-derived neoantigens) are considered as well as the relevance of sequestration as a virulence factor in human disease and its potential role in parasite biology.

Molecular mechanisms of sequestration in malaria.

Cell surface molecules have received intense attention in recent years because of the central roles they play at the interface between the external environment and the cellular interior. Their functions include adhesion to other cells or extracellular matrices, protection against hostile physical, chemical and biological agents and the transport of metabolites into and out of the cell. In addition, cell surface molecules transduce signals across the cell membrane, relaying information inwards and presenting altered characteristics to the exterior as the environment changes.

PfEMP1, polymorphism and pathogenesis.

The virulence of Plasmodium falciparum relative to the other species of malarial parasite which infect humans is thought to be due to this parasites ability to adhere to endothelial cells lining small blood vessels and, in some cases, to its ability to form rosettes with uninfected erythrocytes. The latter phenotype has been found more frequently in cases of severe disease. The former property means that only the younger, asexual, intra-erythrocytic forms circulate whereas the more mature developmental stages are sequestered in the vasculature of a variety of organs. When large numbers of parasites accumulate in a vulnerable target organ such as the brain, the the life-threatening condition of cerebral malaria may result. While the factors that control whether or not cerebral malaria develops are not clearly defined, one crucial determinant my be the endothelial receptors utilised by the infecting isolate. Many such receptors have been identified, including CD36, thrombospondin, ICAM-1, VCAM, E-selectin and chondroitin-4-sulphate. The results of laboratory, field, post-mortem and direct receptor-binding studies indicate that, of the receptors currently identified, ICAM-1 binding is more likely to be associated with the development of cerebral malaria. The molecule expressed on the surface of the infected erythrocyte which mediates adherence to endothelium belongs to a large family of clonally variable antigens encoded by the var genes. The evidence for this conclusion and progress in defining the regions of var-gene products responsible to receptor-specific binding are discussed. Finally, the organization of the var genes within and between parasites is discussed in relation to the evolution of the var-gene family and its functions of antigenic variation and endothelial adhesion.

Native hip joint septic arthritis in 20 adults: Delayed presentation beyond three weeks predicts need for excision arthroplasty

OBJECTIVES Septic arthritis of native hip joints is an uncommon condition in adults in Western Europe, but continues to present a challenge to medical and surgical management. We set out to study the natural history and bacteriology of the disease in this group, with a particular focus on patients requiring excision arthroplasty (EA). METHODS We retrospectively studied 26 secondary referral cases (20 adults) managed by a specialist bone infection unit over a 12 year period. RESULTS Our patient cohort was diverse, affecting all age groups in the presence and absence of co-morbid conditions. The commonest pathogen was Staphylococcus aureus. Of 20 adults studied, five (25%) required EA. Symptom duration prior to presentation was a statistical predictor of the requirement for EA (p<0.003); in particular, symptom duration of over three weeks was strongly associated with requirement for this procedure (p<0.0003). CONCLUSIONS In cases that present promptly, combined surgical drainage and intravenous antibiotics should be expected to eradicate infection and to salvage the femoral head. Cases presenting following a delay are more likely to require EA and subsequent hip reconstruction.

Intravenous antibiotic treatment at home can provide higher quality care.

Editor—The tone of Dilip Nathwani and Peter Daveys article on community based intravenous antibiotic treatment in Britain is unnecessarily negative.1 We agree, however, that outpatient intravenous antibiotic treatment should be driven by a concern for quality rather than as a cost saving practice. Such therapy was developed in the United States because clinicians wanted to maintain quality care for patients with infections requiring intravenous treatment in the face of pressure from third party …

Interations of the Plasmodium falciparum—Infected Erythrocyte with ICAM-1

Erythrocytes infected with the mature forms of the malarial parasite Plasmodium falciparum do not circulate in the peripheral blood but instead adhere to postcapillary venular endothelium (1). The phenomenon is analogous in many ways to lymphocyte adhesion to endothelium in that it is mediated by specific receptor-ligand interactions and must take place under shear flow conditions. Unlike lymphocytes, however, the infected erythrocytes do not transmigrate, but remain adherent for a period of approximately 24 h, during which time parasite development continues, until rupture of the erythrocyte and the release of the next generation of blood-stage parasites. Cytoadherence is thought to be an important contributor to the pathogenesis of severe malaria, since high local concentrations of parasitized cells may significantly affect flow, deplete the blood of metabolites, and release toxic products. Several complications of severe disease, such as cerebral malaria, are characterized by dense packing of infected erythrocytes in the vascular beds of affected organs (2), implying that the ability of the infected cells to localize in deep-tissue vasculature has an important bearing on the clinical outcome.