The 3D7var5.2 (varCOMMON) type var gene family is commonly expressed in non-placental Plasmodium falciparum malaria

Relapse variants in chronic Plasmodium falciparum infections are antigenically distinct from the parental parasites. The variable antigen PfEMP1 expressed at the surface of the infected erythrocyte (IE) is encoded by the var gene family with ≈60 copies per haploid genome. Placental isolates commonly express DBLγ containing subtypes of var genes with homology to either 3D7var5.2 (varCOMMON) or FCR3varCSA. Here we report that varCOMMON related genes are constitutively transcribed in ≈60% of malaria infected children in Gabon. varCOMMON is conserved in field isolates over at least 2.1kb. In 3D7 parasites varCOMMON is present on chromosome 5 (var5.2) and constitutively transcribed in the opposite direction to most other var genes. It lacks a regulatory intron, an acidic terminal segment and ends in telomeric repeat sequences. varCOMMON encodes a large, hypothetical PfEMP1 of a structure similar to previous placenta-binding PfEMP1s but it is not present at the IE-surface. IE of a 3D7 clone (3D7S8) transcribe varCOMMON but express a PfEMP1 distinct from varCOMMON at the surface and adhere to placental tissues through varCOMMON independent novel mechanisms. Our report suggests that expression of varCOMMON type genes is not restricted to placental malaria. © 2003 Published by Elsevier Science B.V.