First they support the hypothesis that all P. falciparum parasites have the capacity to express VSA PAM . This hypothesis is supported by previously published data that all P. falciparum genomes appear to contain at least one paralog of the gene encoding the only known VSA PAM -type antigen, VAR2CSA (11, 14) . Furthermore, this gene is selectively transcribed by placental parasites (and following selection for adhesion to CSA in vitro) and VAR2CSA is expressed on the IE surface (15) (16) (17) .