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M Wahlgren

Publications and source records attributed to M Wahlgren.

At least 37 records · Page 2Linked to original sources
PubMed1999

Plasmodium falciparum: molecular background to strain-specific rosette disruption by glycosaminoglycans and sulfated glycoconjugates.

Rosetting, the adhesion of Plasmodium falciparum-infected erythrocytes to uninfected erythrocytes, is a virulent parasite phenotype associated with the occurrence of severe malaria, e.g., cerebral malaria. Compounds with specific anti-rosetting activity are potential therapeutic agents. Glycosaminoglycans and sulfated glycoconjugates were found to disrupt rosettes in a strain- and isolate-specific manner. Rosette disruption was strongly connected to the presence of N-sulfate groups in heparin/heparan sulfate as demonstrated by modified heparin preparations. This finding was corroborated by the disruption of rosettes with mono- and disaccharides derived from heparin/heparan sulfate that contained N-sulfated glucosamine. Furthermore, heparinase III treatment of erythrocyte cultures infected by FCR3S1 (and to some extent TM 284) P. falciparum strains abolished rosetting. Heparinase III treatment of the uninfected erythrocytes prior to mixing with the infected culture impeded formation of rosettes, indicating that the rosetting receptors at least partially are of glycosaminoglycan nature.

Animals↗
PubMed1999

Rouleaux-forming serum proteins are involved in the rosetting of Plasmodium falciparum-infected erythrocytes.

Excessive sequestration of Plasmodium falciparum-infected (pRBC) and uninfected erythrocytes (RBC) in the microvasculature, cytoadherence, and rosetting, have been suggested to be correlated with the development of cerebral malaria. P. falciparum erythrocyte membrane protein-1 (PfEMP1) is the parasite-derived adhesin which mediates rosetting. Herein we show that serum proteins are crucial for the rosette formation of four strains of parasites (FCR3S1, TM284, TM180, and R29), whereas the rosettes of a fifth strain (DD2) are serum independent. Some parasites, e.g., FCR3S1, can be depleted of all rosettes by washes in heparin and Na citrate and none of the rosettes remain when the parasite is grown in foetal calf serum or ALBUMAX. Rosettes of other parasites are less sensitive; e.g., 20% of TM180 and R29 and 70% of TM284 rosettes still prevail after cultivation. A serum fraction generated by ion-exchange chromatography and poly-ethylene-glycol precipitation restored 50% of FCR3S1 and approx 40 to 100% of TM180 rosettes. In FCR3S1, antibodies to fibrinogen reverted the effect of the serum fraction and stained fibrinogen bound to the pRBC surface in transmission electron microscopy. Normal, nonimmune IgM and/or IgG was also found attached to the pRBC of the four serum-dependent strains as seen by surface immunofluorescens. Our results suggest that serum proteins, known to participate in rouleaux formation of normal erythrocytes, produce stable rosettes in conjunction with the recently identified parasite-derived rosetting ligand PfEMP1.

Animals↗
PubMed1998

Developmental selection of var gene expression in Plasmodium falciparum.

The protozoan Plasmodium falciparum causes lethal malaria. Adhesion of erythrocytes infected with P. falciparum to vascular endothelium and to uninfected red blood cells (rosetting) may be involved in the pathogenesis of severe malaria. The binding is mediated by the antigenically variant erythrocyte-membrane-protein-1 (PfEMP-1), which is encoded by members of the P. falciparum var gene family. The control of expression and switching of var genes seems to lack resemblance to mechanisms operating in variant gene families of other microbial pathogens. Here we show that multiple, distinct var gene transcripts (about 24 or more) can be detected by reverse transcription and polymerase chain reaction in bulk cultures of the rosetting parasite FCR3S1.2, despite the adhesive homogeneity of the cultures. We also detected several var transcripts in single erythrocytes infected with a ring-stage parasite of FCR3S1.2, and found that different var genes are transcribed simultaneously from several chromosomes in the same cell. In contrast, we detected only one var transcript, FCR3S1.2 var-1, which encodes the rosetting PfEMP-1 protein, in individual rosette-adhesive trophozoite-infected cells, and we found only one PfEMP-1 type at the erythrocyte surface by labelling with 125iodine and immunoprecipitation. We conclude that a single P. falciparum parasite simultaneously transcribes multiple var genes but, through a developmentally regulated process, selects only one PfEMP-1 to reach the surface of the host cell.

Adult↗
PubMed1998

Identification of Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) as the rosetting ligand of the malaria parasite P. falciparum.

Severe Plasmodium falciparum malaria is characterized by excessive sequestration of infected and uninfected erythrocytes in the microvasculature of the affected organ. Rosetting, the adhesion of P. falciparum-infected erythrocytes to uninfected erythrocytes is a virulent parasite phenotype associated with the occurrence of severe malaria. Here we report on the identification by single-cell reverse transcriptase PCR and cDNA cloning of the adhesive ligand P. falciparum erythrocyte membrane protein 1 (PfEMP1). Rosetting PfEMP1 contains clusters of glycosaminoglycan-binding motifs. A recombinant fusion protein (Duffy binding-like 1-glutathione S transferase; Duffy binding-like-1-GST) was found to adhere directly to normal erythrocytes, disrupt naturally formed rosettes, block rosette reformation, and bind to a heparin-Sepharose matrix. The adhesive interactions could be inhibited with heparan sulfate or enzymes that remove heparan sulfate from the cell surface whereas other enzymes or similar glycosaminoglycans of a like negative charge did not affect the binding. PfEMP1 is suggested to be the rosetting ligand and heparan sulfate, or a heparan sulfate-like molecule, the receptor both for PfEMP1 binding and naturally formed erythrocyte rosettes.

Amino Acid Sequence↗
PubMed1998

Extensive immunoglobulin binding of Plasmodium falciparum-infected erythrocytes in a group of children with moderate anemia.

Immunoglobulins (Ig) from healthy, nonimmune individuals bind to the surfaces of Plasmodium falciparum-infected erythrocytes (RBC). In order to investigate the presence of this parasite phenotype in wild isolates and its potential association with malarial anemia, we conducted a study of 207 anemic or nonanemic children with malaria in Gabon. Surface Ig binding to infected RBC was detected for 83% of the isolates. No difference in Ig binding between the groups was observed, but all isolates which exhibited extensive Ig binding were found in a group of moderately anemic children.

Adolescent↗
PubMed1998

Age-related buildup of humoral immunity against epitopes for rosette formation and agglutination in African areas of malaria endemicity.

In this report, we show an age-related buildup of agglutinating activity as well as serum activity against rosette formation in children living in areas of Kenya and Gabon where malaria is endemic. Sera from Kenyans in general exhibited a stronger and wider immune response toward the epitopes, probably reflecting a difference in transmission patterns between the two areas. Thus, our results indicate that repeated malaria attacks in areas of endemicity, and consequently exposure to different isolate-specific antigens, will elicit an antibody-mediated response eventually enabling recognition of the majority of rosetting and agglutinating antigens. The correlation between antirosetting and agglutinating capacity was poor in individual cases, indicating that the rosetting epitopes are only a minor part of the highly diverse surface-exposed antigens (mainly PfEMP1) on the surface of parasitized erythrocytes toward which antibodies may react. These data together with our previous findings that the protection against cerebral malaria correlates with presence of antirosetting antibodies shed new light on our understanding of the gradual acquisition of immunity toward severe complications of malarial infection which children reared in areas of endemicity attain.

Adolescent↗
PubMed1998

Multiple adhesive phenotypes linked to rosetting binding of erythrocytes in Plasmodium falciparum malaria.

The cerebral form of severe malaria is associated with excessive intravascular sequestration of Plasmodium falciparum-infected erythrocytes (PRBC). Retention and accumulation of PRBC may lead to occlusion of brain microvessels and direct the triggering of acute pathologic changes. Here we report that by selection, cloning, and subcloning, we have identified rare P. falciparum parasites expressing a pan-adhesive phenotype linked to erythrocyte rosetting, a previously identified correlate of cerebral malaria. Rosetting PRBC not only bound uninfected erythrocytes but also formed autoagglutinates, adhered to endothelial cells, and bound to CD36, immunoglobulins, and the blood group A antigen. The linkage of rosetting, autoagglutination, and cytoadherence involved the coexpression on a single PRBC of ligands with multiple specificities and the binding to two or more receptors on erythrocytes and to at least two other cell adhesion molecules, including a new endothelial cell receptor for P. falciparum-infected erythrocytes. Limited proteolysis that differentially cleaved the rosetting ligand PfEMP1 from the PRBC surface abrogated all the binding phenotypes of these parasites, implicating the variant antigen PfEMP1 as a carrier of multiple ligand specificities. The results encourage the further study of pan-adhesion as a potentially important parasite phenotype in the pathogenesis of severe P. falciparum malaria.

Animals↗
PubMed1998

Identification of Pneumocystis carinii f. sp. hominis gene sequences in filtered air in hospital environments.

To evaluate the risk of a nosocomial spread of Pneumocystis carinii f. sp. hominis (P. carinii hominis), air filter samples from rooms of P. carinii pneumonia (PCP) patients, adjacent corridors, and other hospital environments have been investigated for the presence of P. carinii hominis. Amplified DNA from air filters and sputum or bronchoalveolar lavage samples from the PCP patients have been genotyped with the P. carinii hominis genes of the mitochondrial large-subunit (mtLSU) rRNA and the internal transcribed spacers (ITS1 and ITS2) of the rRNA. Genotypes of the two loci were identified by direct sequencing, and for site 85 of the mtLSU locus, three allele-specific PCR assays were used. P. carinii hominis DNA was identified in the air of five of seven PCP patient rooms and in the air of two of four air filtrations from the ward corridors. The P. carinii hominis genotypes were the same in four of the five room air samples as those in the corresponding patients, suggesting a risk of person-to-person transmission of P. carinii hominis from PCP patients. Three of 16 air samples collected in infectious disease wards without the presence of PCP patients and one sample from a cardiology unit in a separate hospital building were also positive, which further strengthens the possibility of acquisition of P. carinii hominis from the environment.

Air Microbiology↗
PubMed1998

The time course of cytoadhesion, immunoglobulin binding, rosette formation, and serum-induced agglutination of Plasmodium falciparum-infected erythrocytes.

We describe morphologic characteristics of acridine orange-stained Plasmodium falciparum-infected erythrocytes and the sequential expression of several adhesion phenomena. In particular, we have studied when the adhesive and antigenic modifications appear on the infected erythrocyte surface that mediate binding to C32 melanoma cells (cytoadherence) or to erythrocytes (rosette formation) during a complete 48-hr life cycle of the parasite. The C32 melanoma cell binding started at about 12 hr and was seen during the whole life cycle with a peak around 28 hr (650 infected erythrocytes/100 C32 melanoma cells). Rosettes started to appear and immunoglobulin was found bound to the parasitized red blood cell (PRBC) somewhat later (16-20 hr). These adhesive events culminated at the mid-trophozoite/schizont stage (24-36 hr) with rosette formation and an immunoglobulin binding rate of about 50%, which decreased to about half of the peak values at the end of the life cycle. Serum-induced agglutination of the infected erythrocytes was also most extensive at 24-36 hr, but agglutination was seen with all late stage parasites, i.e., both trophozoites and schizonts at 24-48 hr of age. Taken together, adhesion to C32 melanoma cells starts prior to that of rosette formation, immunoglobulin binding, or serum-induced agglutination.

Agglutination Tests↗
PubMed1998

Enrichment of immunoglobulin binding Plasmodium falciparum-infected erythrocytes using anti-immunoglobulin-coated magnetic beads.

It has been shown that nonimmune, human immunoglobulins are bound to the surface of certain strains of Plasmodium falciparum-infected erythrocytes. We describe a novel way of enriching parasitized red blood cells (pRBC) for immunoglobulin binding/rosette formation using Dynabeads coated with antibodies raised against human immunoglobulins. Whole P. falciparum cultures were mixed with the precoated beads for approximately 120 min at room temperature, and the bound pRBC were isolated by magnetic force. The nonbound cell fraction contained ring-infected pRBC, immunoglobulin-negative, trophozoite-infected pRBC, and uninfected erythrocytes. A consistent elevation in the immunofluorescence and rosette formation rates of 100% and 86% respectively, was detected after the first enrichment and subcultivation. Protein A or G were also found to support binding of pRBC through surface-expressed immunoglobulin. The Dynabead technique is a novel way of enriching pRBC based on the immunoglobulin-binding capacity of the infected erythrocyte.

Animals↗
PubMed1997

PECAM-1/CD31, an endothelial receptor for binding Plasmodium falciparum-infected erythrocytes.

Excessive binding of Plasmodium falciparum-infected red blood cells (pRBCs) to the vascular endothelium (cytoadherence) and to uninfected erythrocytes (rosetting) may lead to occlusion of the microvasculature and thereby contribute directly to the acute pathology of severe human malaria. A number of endothelial receptors have been identified as targets for the pRBCs, including CD36, intercellular adhesion molecule-1 (ICAM-1) and chondroitin-4-sulfate (CSA). In vitro, CD36 is the most frequent target of strains from patients with mild as well as severe P. falciparum malaria, but is expressed at low levels on the cerebral microvasculature and therefore seems unlikely to be involved in the evolution of cerebral disease. Strains of P. falciparum that form rosettes are associated both with the occurrence of cerebral malaria and severe anemia. Here we report that malaria-infected RBCs adhere to platelet/endothelial cell adhesion molecule-1 (PECAM-1/CD31) on the vascular endothelium. pRBCs bind to endothelial cells, to PECAM-1/CD31 transfected cells, and directly to recombinant PECAM-1/CD31 absorbed onto plastic. Soluble PECAM-1/CD31 and monoclonal antibodies specific for the amino-terminal segment of PECAM-1/CD31 (domains 1-4) blocked the binding. Interferon-gamma (IFN-gamma)-essential for the development of cerebral malaria in the mouse-was found to augment adhesion of human pRBCs to PECAM-1/CD31 on endothelial cell monolayers. Our results suggest that PECAM-1/CD31 is a virulence-associated endothelial receptor of P. falciparum-infected RBCs.

Animals↗
PubMed1996

Novel fibrillar structure confers adhesive property to malaria-infected erythrocytes.

Infections with the malaria parasite Plasmodium falciparum are characterized by sequestration of erythrocytes infected by mature forms of the parasite. Sequestration seems critical for the survival of the parasite, but may lead to excessive binding in the microvasculature and death of the human host. We report here that a novel electrondense fibrillar structure, containing immunoglobulins M or M and G, is found at the surface of infected erythrocytes that adhere to host cells. In cases of cerebral malaria, fibrillar strands are also seen in the microvasculature at autopsy. Our findings may explain the adhesive mechanism by which malaria-infected erythrocytes cause the vascular obstruction seen in complicated malaria infections.

Cell Adhesion↗
PubMed1995

Adhesion of Plasmodium falciparum-infected erythrocytes to human cells and secretion of cytokines (IL-1-beta, IL-1RA, IL-6, IL-8, IL-10, TGF beta, TNF alpha, G-CSF, GM-CSF.

The scientific interest in the physical interaction of Plasmodium falciparum-infected erythrocytes with host cells stems from the suggestion that excessive binding in the microvasculature leads to severe malaria. The authors studied, therefore, two parasites for their ability to adhere to normal human cells and to induce cytokine production, one parasite lacking a binding capacity (DD2) and one which adhered to CD36+ transfected CHO cells (MCAMP). The MCAMP parasites readily bound to platelets and erythrocytes and to monocytes, polymorphonuclear granulocytes and EBV-transformed B cells as seen by light and electron microscopy. Platelets were frequently attached in large numbers to the infected erythrocyte surface and groups of infected erythrocytes were sometimes held together by several platelets. Nine out of 17 cytokines tested were found to be secreted into the culture supernatants after 35 h of co-cultures containing monocytes or unfractionated peripheral blood mononuclear cells (PBMC) and parasites (IL-1RA, IL-6, IL-8, IL-10, TGF beta, TNF alpha, G-CSF, IL-1-beta, and GM-CSF). Three additional cytokines were also present in low levels (< 200 pg/ml, IL-2, IL-4, IFN gamma) in the culture supernatants after incubation of the cells for 4 days. TNF alpha, IL-RA, and IL-8 were secreted from polymorphonuclear granulocytes, LGLs and T cells. Platelets and, to a lesser degree, monocytes and T cells secreted large amounts of TGF beta (10-30 ng/ml). Cytokines may participate in the pathogenesis but also the suppression of immune responses seen during acute malarial infections.

Animals↗
PubMed1994

Natural protection against severe Plasmodium falciparum malaria due to impaired rosette formation.

Genes for two lethal diseases, thalassemia and sickle cell anemia, are favored by evolution because, in their heterozygous form, they protect against cerebral malaria. Rosette formation, the binding of uninfected red cells (RBCs) to Plasmodium falciparum-infected RBCs (PRBCs), has previously been found to be associated with cerebral malaria, the most important severe manifestation of P falciparum malaria. We show here that thalassemic RBCs and, under certain conditions, even hemoglobin S (HbS)-containing RBCs possess an impaired ability to bind to PRBCs, forming small and weak erythrocyte rosettes compared with rosettes formed by normal RBCs. This decreased rosetting ability is associated with the small size of the thalassemic RBCs and with distortion of the mechanical properties of HbS-containing RBCs. The impairment of rosette formation may hinder the development of cerebral malaria by abatement of sequestration.

Anemia, Sickle Cell↗
PubMed1994

Rosetting.

Why do some individuals get severe falciparum malaria while others don't? Rosetting (the binding of uninfected erythrocytes to Plasmodium falciparum-infected erythrocytes), together with endothelial cytoadherence, has been shown to play a crucial role in the obstruction of the microvosculoture in P. falciparum malaria. Here, Mats Wahlgren, Victor Fernandez, Carin Scholonder and Johan Carlson review the literature surrounding rosetting.

Journal Article↗