Abstract
BackgroundMembers 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.MethodsIn 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.ResultsVar3 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.ConclusionsCollectively, 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.
Highlights
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 selected lines, 3D7VAR3 and FCR3VAR3, showed markedly higher levels of var3 transcripts, PFI1820w and IT4var3, than the unselected lines and the var3 transcript levels were similar to those observed for var genes in vivo [53] and other adhesion-selected in-vitro parasite cultures with verified erythrocyte surface expression of PfEMP1 [20,28]
The two var3 genes, PFI1820w and PFF0020c, were the dominant var transcripts during the entire cycle with the exception at 0 h post magnet-activated cell sorting (MACS) (PM), with a peak in transcript level at 19 h PM corresponding to mid ring stages (Figure 3) and exhibits a transcription pattern similar to var2csa in a VAR2CSA-expressing parasite line [43] and four group A var genes in the 3D7-Lib parasite line [45]
Summary
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, var, var2csa and var 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. The PfEMP1 family is encoded by approximately 60 var genes per parasite genome [6,15], which can be divided in two four groups A-E based on their 5 ́upstream region [16,17]. Apart from these, most parasite genomes contain a set of vars encoding more diverse domain cassettes not spanning the full length genes [23]. Sequence analysis has shown that only the DBLζDBLε part of VAR3, which is 99% identical between VAR3 sequences, is unique to the protein sub-family [23]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
