Molecular & Biochemical Parasitology 148 (2006) 117–124 VAR2CSA is the principal ligand for chondroitin sulfate A in two allogeneic isolates of Plasmodium falciparum Michael F. Duffy a,∗ , Alexander G. Maier b , Timothy J. Byrne a , Allison J. Marty b,c , Salenna R. Elliott a , Matthew T. O’Neill b , Paul D. Payne a , Stephen J. Rogerson a , Alan F. Cowman b , Brendan S. Crabb b , Graham V. Brown a a The Department of Medicine, The University of Melbourne, The Royal Melbourne Hospital, Parkville, Vic. 3050, Australia b The Walter and Eliza Hall Institute of Medical Research, 19 Royal Parade Parkville, Vic. 3050, Australia c Microbiology Department, Monash University, Clayton, Vic. 3800, Australia Received 10 October 2005; received in revised form 6 March 2006; accepted 13 March 2006 Available online 7 April 2006 Abstract Malaria during pregnancy causes serious disease that is associated with sequestration in the placenta of Plasmodium falciparum infected erythrocytes that adhere to several host receptors, including chondroitin sulfate A (CSA). The principal CSA binding ligand associated with placental sequestration is the P. falciparum erythrocyte membrane protein 1 (PfEMP1), encoded by the var2csa gene. We disrupted the var2csa gene in two allogeneic parasites and ablated CSA binding. However, in one parasite line we were able to re-select for adhesion to bovine trachea CSA associated with transcription of two var genes, var-CS2 and varP. Parasites transcribing parts of var-CS2 and varP were present in the placentae of some infected women but the mutant parasites that transcribed var-CS2 and varP were recognized by sera from men and pregnant women independent of parity. This work raises the possibility that the PfEMP1 molecules encoded by var-CS2 and varP may be minor contributors to placental malaria but also confirms the importance of the immunodominant, conserved var2csa PfEMP1s in pregnancy associated malaria and strengthens the case for var2csa as a pregnancy-specific malaria vaccine. © 2006 Elsevier B.V. All rights reserved. Keywords: Malaria; Pregnancy; CSA; var2csa; Adhesion; Transfection 1. Introduction In areas of endemic transmission the burden of malarial dis- ease falls primarily on children and pregnant women. Malaria in pregnancy causes mortality and morbidity principally through maternal anemia and low birth weight [1]. Susceptibility dur- ing pregnancy of previously immune women is associated with sequestration within the placenta of parasitised red blood cells (pRBCs) that express unique variant surface antigens (VSAs) [2]. The restriction of these VSAs to pregnant women correlates with the restricted adhesion phenotype observed in placental parasites. The host receptors implicated in adhesion of pRBCs Abbreviations: pRBCs, parasitised red blood cells; CSA, chondroitin sulfate A; PfEMP1, P.falciparum erythrocyte membrane protein 1; VSA, variant surface antigen; Q-RT-PCR, quantitative RT-PCR; GalNAc, N-aetylgalactosamine ∗ Corresponding author. Tel.: +61 3 8344 3267; fax: +61 3 9347 1863. E-mail address: mduffy@unimelb.edu.au (M.F. Duffy). to placenta are CSA, hyaluronic acid and non-immune globulins [3–5] whereas other host receptors, including CD36 and ICAM- 1, mediate sequestration of pRBCs in non-pregnant individuals. Presumably the placenta selects for parasites that bind CSA by providing a novel host receptor in a form of CSA that is absent or not accessible to pRBCs in non-pregnant individuals. Because pRBCs expressing the CSA adhesion ligand are not selected for in non-pregnant individuals [6], malaria-exposed women do not possess immunity to pRBCs expressing the CSA adhesion ligand prior to pregnancy. Plasmodium falciparum erythrocyte membrane protein-1 (PfEMP1) molecules are expressed on the surface of the pRBCs and mediate adhesion of the pRBCs to various host receptors. Each of the approximately 60 members of the var multigene fam- ily present within a single parasite encodes a different PfEMP1 [7]. var genes are subject to transcriptional control such that a single full-length var gene transcript is dominant at one time within a parasite [8,9]. Switching between the expressed var 0166-6851/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.molbiopara.2006.03.006