An infection with Plasmodium falciparum may lead to severe malaria as a result of excessive binding of infected erythrocytes in the microvasculature. Vascular adhesion is mediated by P. falciparum erythrocyte membrane protein-1 (PfEMP1), which is encoded for by highly polymorphic members of the var-gene family. Here, we profile var gene transcription in fresh P. falciparum trophozoites from Ugandan children with malaria through var-specific DBL1␣-PCR amplification and sequencing. A method for subsectioning region alignments into homology areas (MOTIFF) was developed to examine collected sequences. Specific PfEMP1-DBL1␣ amino acid motifs correlated with rosetting and severe malaria, with motif location corresponding to distinct regions of receptor interaction. The method is potentially applicable to other families of variant proteins and may be useful in identifying sequencephenotype relationships. The results suggest that certain PfEMP1 sequences are predisposed to inducing severe malaria.homology areas ͉ antigenic variation ͉ rosetting P lasmodium falciparum malaria infection is one of the primary contributors to childhood mortality in many developing countries. Despite exhaustive research efforts, no vaccine capable of conferring an adequate level of immunity has been developed to date. Vaccine development is encouraged by the fact that children attain conditional immunity to severe malaria after relatively few infections. However, a lack of insight into the molecular interplay between the parasite and the host continues to thwart efforts at vaccine development. One of the key factors in this process is the ability of the parasite to continually express a plethora of antigenic variants of gene families, whose selection appears to correspond with interactions with the host immune system.Severe malaria, a highly lethal form of the disease, is, in part, attributable to the sequestration of P. falciparum-infected erythrocytes (IE) and uninfected erythrocytes in postcapillary venules of the brain, the lungs, or other organs (1). P. falciparum expresses a number of proteins at the erythrocyte surface that are closely involved in the excessive sequestration characteristic of severe malaria. The polypeptide most closely scrutinized to date, PfEMP1, is a large 200-to 400-kDa clonally variant antigen encoded by a repertoire of Ϸ60 var genes (2). The var genes present a two-exon structure encoding a conserved C terminus that contains a predicted transmembrane region and a polymorphic submodular N terminus. This N terminus region possesses a number of cysteine-rich domains that are intimately involved in the sequestration of the parasite in the microvasculature (3-5). The Duffy binding-like domain-␣ (DBL1␣) located in the Nterminal head structure of PfEMP1 mediates rosetting and endothelial binding of IE. These binding processes occur by means of a range of different receptors, including heparan sulfate, complement receptor 1, and/or the blood group A antigen (6-9). Rosetting and endothelial binding are intimately associa...

Antibodies to the C terminus of the Plasmodium falciparum merozoite surface protein, PfMSP-1 19 , may inhibit merozoite invasion or block the effects of inhibitory antibodies. Here, using a competition enzymelinked immunosorbent assay and antibody binding to wild-type and mutated recombinant proteins, we show that there are marked variations between individuals in the fine specificity of naturally acquired anti-MSP-1 19 antibodies. Furthermore, although neither the prevalence nor the concentration of total anti-MSP-1 19 antibodies was associated with resistance to malaria in African children, significant associations were observed between antibody fine specificity and subsequent risk of infection and high-density parasitemia during a follow-up period. Thus, the fine specificity of naturally acquired human anti-MSP-1 19 antibodies is crucial in determining their function. Future field studies, including the evaluation of PfMSP-1 vaccine trials, should include assays that explore antibody fine specificity as well as titer.

The Plasmodium falciparum serine repeat antigen (SERA) is one of the blood stage malaria vaccine candidates. The malaria genome project has revealed that SERA is a member of the SERA multigene family consisting of eight SERA homologues clustered on chromosome 2 and one SERA homologue on chromosome 9. Northern blotting and real time quantitative reverse transcription-PCR with five independent parasite strains, including three allelic representative forms of the SERA gene, have shown that all of the SERA homologues are transcribed most actively at trophozoite and schizont stages and that SERA5 (SERA/SERP) is transcribed predominantly among the family. Polyclonal antibodies were raised against recombinant proteins representing the Nterminal portions of four significantly transcribed SERA homologues (SERA3 to -6) in the center of the cluster on chromosome 2. Using these antibodies, indirect immunofluorescence microscopy detected the expression of SE-RA3 to -6, with similar localization, in all trophozoite-and schizont-infected erythrocytes. We have examined 40 sera from Ugandan adults for their antibody reactivity and found that enzyme-linked immunosorbent assay titer against SERA5 N-terminal domain, but not against other SERA proteins, is positively correlated with the inhibition of in vitro parasite growth by individual sera. Our data confirm the usefulness of the N-terminal domain of SERA5 as a promising malaria candidate vaccine.

Severe human malaria is attributable to an excessive sequestration of Plasmodium falciparum–infected and uninfected erythrocytes in vital organs. Strains of P. falciparum that form rosettes and employ heparan sulfate as a host receptor are associated with development of severe forms of malaria. Heparin, which is similar to heparan sulfate in that it is composed of the same building blocks, was previously used in the treatment of severe malaria, but it was discontinued due to the occurrence of serious side effects such as intracranial bleedings. Here we report to have depolymerized heparin by periodate treatment to generate novel glycans (dGAG) that lack anticoagulant-activity. The dGAGs disrupt rosettes, inhibit merozoite invasion of erythrocytes and endothelial binding of P. falciparum–infected erythrocytes in vitro, and reduce sequestration in in vivo models of severe malaria. An intravenous injection of dGAGs blocks up to 80% of infected erythrocytes from binding in the micro-vasculature of the rat and releases already sequestered parasites into circulation. P. falciparum–infected human erythrocytes that sequester in the non-human primate Macaca fascicularis were similarly found to be released in to the circulation upon a single injection of 500 μg of dGAG. We suggest dGAGs to be promising candidates for adjunct therapy in severe malaria.

MalariaGEN is a data-sharing network that enables groups around the world to work together on the genomic epidemiology of malaria. Here we describe a new release of curated genome variation data on 7,000 Plasmodium falciparum samples from MalariaGEN partner studies in 28 malaria-endemic countries. High-quality genotype calls on 3 million single nucleotide polymorphisms (SNPs) and short indels were produced using a standardised analysis pipeline. Copy number variants associated with drug resistance and structural variants that cause failure of rapid diagnostic tests were also analysed.  Almost all samples showed genetic evidence of resistance to at least one antimalarial drug, and some samples from Southeast Asia carried markers of resistance to six commonly-used drugs. Genes expressed during the mosquito stage of the parasite life-cycle are prominent among loci that show strong geographic differentiation. By continuing to enlarge this open data resource we aim to facilitate research into the evolutionary processes affecting malaria control and to accelerate development of the surveillance toolkit required for malaria elimination.