The Plasmodium falciparum variant erythrocyte surface antigens known as PfEMP1, encoded by the var gene family, are thought to play a crucial role in malaria pathogenesis because they mediate adhesion to host cells and immuno-modulation. Var genes have been divided into three major groups (A, B and C) and two intermediate groups (B/A and B/C) on the basis of their genomic location and upstream sequence. We analysed expressed sequence tags of the var gene DBLα domain to investigate var gene transcription in relation to disease severity in Malian children. We found that P. falciparum isolates from children with cerebral malaria (unrousable coma) predominantly transcribe var genes with DBLα1-like domains that are characteristic of Group A or B/A var genes. In contrast, isolates from children with equally high parasite burdens but no symptoms or signs of severe malaria (hyperparasitaemia patients) predominantly transcribe var genes with DBLα0-like domains that are characteristic of the B and C-related var gene groups. These results suggest that var genes with DBLα1-like domains (Group A or B/A) may be implicated in the pathogenesis of cerebral malaria, while var genes with DBLα0-like domains promote less virulent malaria infections.

Determining the diversity of PfEMP1 sequences expressed by Plasmodium falciparum-infected erythrocytes isolated from placentas is important for attempts to develop a pregnancy-specific malaria vaccine. The DBL␥ and var2csa DBL3x domains of PfEMP1 molecules are believed to mediate placental sequestration of infected erythrocytes, so the sequences encoding these domains were amplified from the cDNAs of placental parasites by using degenerate oligonucleotides. The levels of specific var cDNAs were then determined by quantitative reverse transcription-PCR. Homologues of var2csa DBL3x were the predominant sequences amplified from the cDNAs of most placental but not most children's parasites. There was 56% identity between all placental var2csa sequences. Many different DBL␥ domains were amplified from the cDNAs of placental and children's isolates. var2csa transcripts were the most abundant var transcripts of those tested in 11 of 12 placental isolates and 1 of 6 children's isolates. Gravidity did not affect the levels of var2csa transcripts. We concluded that placental malaria is frequently associated with transcription of var2csa but that other var genes are also expressed, and parasites expressing high levels of var2csa are not restricted to pregnant women. The diversity of var2csa sequences may be important for understanding immunity and for the development of vaccines for malaria during pregnancy.

Spontaneous binding of infected erythrocytes to uninfected erythrocytes to form rosettes is a property of some strains of Plasmodium falciparum that is linked to severe complications of malaria. Curdlan sulfate (CRDS) is a sulfated glycoconjugate compound that is chemically similar to known rosette-inhibiting drugs such as heparin. CRDS has previously been shown to have antimalarial activity in vitro and is safe for clinical use. Here we show that CRDS at therapeutic levels (10 to 100 g/ml) significantly reduces rosette formation in vitro in seven P. falciparum laboratory strains and in a group of 18 African clinical isolates. The strong ability to inhibit rosetting suggests that CRDS has the potential to reduce the severe complications and mortality rates from P. falciparum malaria among African children. Our data support further clinical trials of CRDS.Despite decades of research, malaria still claims an estimated 1 million lives per year in sub-Saharan Africa, and severe complications, such as cerebral malaria, remain relatively common (19). Treatment for malaria involves the use of antimalarial drugs that kill the parasite, along with supportive measures, such as the provision of intravenous fluids and blood transfusion as required. Progress in understanding the pathogenesis of malaria has led to the possibility of designing therapies that target factors that contribute to severe disease in order to ameliorate the clinical complications and reduce the number of deaths from malaria.Rosetting is the spontaneous binding of noninfected erythrocytes to erythrocytes infected with mature asexual bloodstage Plasmodium parasites (reviewed in reference 14). In Plasmodium falciparum malaria, rosetting is associated with high levels of parasitemia (16) and with disease severity in African children (13,17), especially cerebral malaria (2). Other Plasmodium species also rosette, although it is only in P. falciparum that rosetting is linked to severe disease, probably because of the additional cytoadhesion properties that may act in concert with rosetting to cause microvascular obstruction (8,14). Rosetting in P. falciparum is mediated by heterogeneous mechanisms involving specific members of the parasite variant antigen family PfEMP1 (15), which are expressed on the surface of infected erythrocytes and which binding to a variety of receptors on uninfected red cells, such as complement receptor 1 (CR1), heparan sulfate-like sugars, and ABO blood group oligosaccharides (reviewed in reference 14).Previous work has shown that rosettes can be disrupted by sulfated glycoconjugate compounds such as heparin and fucoidan (1, 12), but the anticoagulant effects of these drugs prevent their use as treatments for severe malaria (19). Curdlan sulfate (CRDS; a semisynthetic sulfated 133-␤-D-glucan) has been shown to inhibit P. falciparum invasion in vitro (6) and is safe for use by adult patients with severe malaria (5). It was hypothesized that CRDS might be effective against P. falciparum rosetting (5) because of the chemical similari...

Background: Sensitive detection of parasite surface antigens expressed on erythrocyte membranes is necessary to further analyse the molecular pathology of malaria. This study describes a modified biotin labelling/osmotic lysis method which rapidly produces membrane extracts enriched for labelled surface antigens and also improves the efficiency of antigen recovery compared with traditional detergent extraction and surface radio-iodination. The method can also be used with ex-vivo parasites.