SltlmlilaryAdherence of Plasmodium fakiparum-infected erythrocytes to cerebral postcapillary venular endothelium is believed to be a critical step in the development of cerebral malaria. Some of the possible receptors mediating adherence have been identified, but the process of adherence in vivo is poorly understood. We investigated the role of carbohydrate ligands in adherence, and we identified chondroitin sulfate (CS) as a specific receptor for P. falciparum-infected erythrocytes.Parasitized cells bound to Chinese hamster ovary (CHO) cells and C32 melanoma cells in a chondroitin sulfate-dependent manner, whereas glycosylation mutants lacking chondroitin sulfate A (CSA) supported little or no binding. Chondroitinase treatment of wild-type CHO cells reduced binding by up to 90%. Soluble CSA inhibited binding to CHO cells by 99.2 _+ 0.2% at 10 mg/ml and by 72.5 _+ 3.8% at 1 mg/ml, whereas a range of other glycosaminoglycans such as heparan sulfate had no effect. Parasite lines selected for increased binding to CHO cells and most patient isolates bound specifically to immobilized CSA. We conclude that P. falciparum can express or expose proteins at the surface of the infected erythrocyte that mediate specific binding to CSA. This mechanism of adherence may contribute to the pathogenesis of P. J~l-ciparum malaria, but has wider implications as an example of an infectious agent with the capacity to bind specifically to cell-associated or immobilized CS.

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SltlmlilaryAdherence of Plasmodium fakiparum-infected erythrocytes to cerebral postcapillary venular endothelium is believed to be a critical step in the development of cerebral malaria. Some of the possible receptors mediating adherence have been identified, but the process of adherence in vivo is poorly understood. We investigated the role of carbohydrate ligands in adherence, and we identified chondroitin sulfate (CS) as a specific receptor for P. falciparum-infected erythrocytes.Parasitized cells bound to Chinese hamster ovary (CHO) cells and C32 melanoma cells in a chondroitin sulfate-dependent manner, whereas glycosylation mutants lacking chondroitin sulfate A (CSA) supported little or no binding. Chondroitinase treatment of wild-type CHO cells reduced binding by up to 90%. Soluble CSA inhibited binding to CHO cells by 99.2 _+ 0.2% at 10 mg/ml and by 72.5 _+ 3.8% at 1 mg/ml, whereas a range of other glycosaminoglycans such as heparan sulfate had no effect. Parasite lines selected for increased binding to CHO cells and most patient isolates bound specifically to immobilized CSA. We conclude that P. falciparum can express or expose proteins at the surface of the infected erythrocyte that mediate specific binding to CSA. This mechanism of adherence may contribute to the pathogenesis of P. J~l-ciparum malaria, but has wider implications as an example of an infectious agent with the capacity to bind specifically to cell-associated or immobilized CS.

Fragment size in the Block 2 repetitive region of merozoite surface protein 1 (MSP1) has commonly been used as a molecular marker in studies of malaria transmission dynamics and host immunity in Plasmodium falciparum malaria. In this study, we further explore the genetic variation in MSP-1 Block 2 underlying potential problems faced while studying the immune responses elicited by this vaccine target and while using it as a molecular marker in epidemiologic investigations. We describe the distribution of a new Block 2 recombinant allele family in samples collected from western Kenya and other malarious regions of the world and provide evidence that this allele family is found worldwide and that all MR alleles most likely originated from a single recombination event. We test whether the number of tandem repeats (i.e. fragment size) can be considered neutral in an area of high transmission in western Kenya. In addition, we investigate the validity of the assumption that Block 2 alleles of the same size and allele family are identical by examining MSP1 Block 2 amino acid sequences obtained from full-length MSP-1 clones generated from infected Kenyan children and find that this assumption does not hold. We conclude that the worldwide presence of a new allele family, the effect of positive natural selection, and the lack of conserved amino acid motifs within alleles of the same size suggest a higher level of complexity that may hamper our ability to elucidate allele family specific immune responses elicited by this vaccine target and its overall use as genetic marker in other types of epidemiologic investigations.