Genetic diversity of the DBLα region in Plasmodium falciparum var genes among Asia-Pacific isolates

In Plasmodium falciparum a highly polymorphic multi-copy gene family, var. encodes the variant surface antigen P. falciparum erythrocyte membrane protein 1 (PtTEMP1), which has an important role in cytoadherence and immune evasion, Using previously described universal PCR primers for the first Duffy binding-like domain (DBLalpha) of car we analysed the DBLalpha repertoires of Dd2 (originally from Thailand) and eight isolates front the Solomon Islands (n = 4), Philippines (n = 2). Papua New Guinea (n = 1) and Africa (n = 1). We found 15-32 unique DBLalpha sequence types among these isolates and estimated detectable DBLalpha repertoire sizes ranging from 33-38 to 52-57 copies per genome. Our data suggest that var gene repertoires generally consist of 40-50 copies per genome. Eighteen DBLalpha sequences appeared in more than one Asia-Pacific isolate kith the number of sequences shared between any two isolates ranging front 0 to 6 (mean = 2.0 +/- 1.6). At the amino acid level DBLalpha sequence similarity within isolates ranged from 45.2 +/- 7.1 to 50.2 +/- 6.9%, and was not significantly different front the DBLalpha amino acid sequence similarity among isolates (P > 0.1). Comparisons with published sequences also revealed little overlap among DBLalpha sequences from different regions. High DBLalpha sequence diversity and minimal overlap among these isolates suggest that the global var gene repertoire is immense, and may potentially be selected for by the host's protective immune response to the tar gene products, PfEMP1. Crown Copyright (C) 2002 Published by Elsevier Science B.V. All rights reserved.