Two DBLγ subtypes are commonly expressed by placental isolates of Plasmodium falciparum

Abstract

Adhesion to chondroitin sulfate A (CSA), a distinguishing feature of malaria parasites obtained from the human placenta, might be mediated by the Duffy-binding-like (DBL) γ domain of the variant surface antigen Plasmodium falciparum erythrocyte membrane protein-1 (PfEMP1). We studied transcription of var genes (that encode PfEMP1) in placental parasites by amplifying and sequencing DBLγ fragments from genomic DNA and cDNA of field isolates collected in western Kenya. We amplified DBLγ fragments with divergent sequences from individual isolates by using various sequence-specific or degenerate primers. Transcripts detected with degenerate primers clustered phylogenetically within two DBLγ subtypes with homology to chr5_1.gen_150 or FCR3.varCSA. Interestingly, the DBLα encoded by chr5_1.gen_150 was recently found to be commonly expressed by placental isolates from Malawi (Mol. Biochem. Parasitol. 185 (2002) 1207). The findings are consistent with earlier serologic evidence that surface antigens of placental parasites have conserved features, and suggest that vaccines based on DBLγ may only need to target a limited number of variants.