The online version of this article (doi:10.1186/1475-2875-11-129) contains supplementary material, which is available to authorized users.
The authors declare that they have no competing interests.
CWW carried out molecular biology studies, analysed data and wrote the paper. TL and TGT participated in the design, coordination and analysis of the study and helped to draft the manuscript. LT designed and carried out molecular biology studies, analysed data and helped to draft the manuscript. DCB, SBS, AMM and MA carried out molecular biology studies and revised the manuscript. PAM and JPL participated in the coordination of the study and revised the manuscript. All authors read and approved the final manuscript.
Members of the Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) adhesion antigen family are major contributors to the pathogenesis of P. falciparum malaria infections. The PfEMP1-encoding var genes are among the most diverse sequences in nature, but three genes, var1, var2csa and var3 are found conserved in most parasite genomes. The most severe forms of malaria disease are caused by parasites expressing a subset of antigenically conserved PfEMP1 variants. Thus the ubiquitous and conserved VAR3 PfEMP1 is of particular interest to the research field. Evidence of VAR3 expression on the infected erythrocyte surface has never been presented, and var3 genes have been proposed to be transcribed and expressed differently from the rest of the var gene family members.
In this study, parasites expressing VAR3 PfEMP1 were generated using anti-VAR3 antibodies and the var transcript and PfEMP1 expression profiles of the generated parasites were investigated. The IgG reactivity by plasma from children living in malaria-endemic Tanzania was tested to parasites and recombinant VAR3 protein. Parasites from hospitalized children were isolated and the transcript level of var3 was investigated.
Var3 is transcribed and its protein product expressed on the surface of infected erythrocytes. The VAR3-expressing parasites were better recognized by children´s IgG than a parasite line expressing a Group B var gene. Two in 130 children showed increased recognition of parasites expressing VAR3 and to the recombinant VAR3 protein after a malaria episode and the isolated parasites showed high levels of var3 transcripts.
Collectively, the presented data suggest that var3 is transcribed and its protein product expressed on the surface of infected erythrocytes in the same manner as seen for other var genes both in vitro and in vivo. Only very few children exhibit seroconversion to VAR3 following a malaria episode requiring hospitalization, supporting the previous conclusion drawn from var3 transcript analysis of parasites collected from children hospitalized with malaria, that VAR3 is not associated with severe anaemia or cerebral malaria syndromes in children.
Additional file 1: Specific var gene primers used for Q-RT PCR. (PDF 47 KB)12936_2012_2116_MOESM1_ESM.pdf
Additional file 2: Primers used for Plasmodium falciparum erythrocyte protein 1 full length (FL) and multi-domain expression. (PDF 52 KB)12936_2012_2116_MOESM2_ESM.pdf
Additional file 3: Var gene transcript levels of Plasmodium falciparum IT4var59 parasites. Var gene transcript levels of IT4var59 parasites relative to the average of two internal control genes. The average of control gene transcript levels is set to 100. The distribution of var transcripts is also shown (circular diagram). Transcript levels were measured by quantitative PCR using a set of primers that amplify 56 var genes from clone IT/FCR3. The grouping of var genes are as previously described [ 16, 17, 23]. (PDF 163 KB)
Additional file 4: Transcript levels of var3 in patient parasite isolates. Transcript levels of var3-DBLε8 in P. falciparum parasites isolated from 130 hospitalized children (little box; red dots: patient A and B) and the var subtype transcript levels in patient parasite isolates, A and B. The levels are relative to the average of two internal control genes, which are normalized to 100. Transcript levels were measured by quantitative PCR using a set of 42 subtyping quantitative primers [ 37]. (PDF 128 KB)
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- Evidence for in vitro and in vivo expression of the conserved VAR3 (type 3) plasmodium falciparum erythrocyte membrane protein 1
Christian W Wang
Dominique C Bengtsson
Pamela A Magistrado
Sanne S Berger
Andrea M Marquard
John P Lusingu
Thor G Theander
- BioMed Central
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