Differential changes in Plasmodium falciparum var transcription during adaptation to culture

Plasmodium falciparum erythrocyte membrane protein 1, which is encoded by the var multigene family, is expressed on the surface of P. falciparum-infected erythrocytes and has been implicated in many of the complications associated with falciparum malaria. Transcriptional switching of var is commonly investigated using in vitro cultured parasites, because parasite material from patients is limited. We investigated the affect of short-term in vitro cultivation on var gene transcription in patient samples. A significant reduction in the overall abundance of var transcripts was observed during the first ∼10 days of culture. The rate of down-regulation was not constant among all var genes; genes with an upsA, -D, and -E 5′ flanking region had a significantly faster rate than genes with an upsB or -C flanking region. These results have significant implications for the investigation of associations between var transcription and clinical manifestations usingparasites that have been enriched by in vitro culture.