Evidence for in vitro and in vivo expression of the conserved VAR3 (type 3) plasmodium falciparum erythrocyte membrane protein 1

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.

Cytoadhesion to gC1qR through Plasmodium falciparum Erythrocyte Membrane Protein 1 in Severe Malaria

“…Similarly to previous in vitro studies with P . falciparum 3D7 [50,51], PFD0625c was also detected in the selected and unselected 3D7 line, which may be due to some degree of relaxed transcription in 3D7 [52]. The PFD0020c specifically up-regulated in Pf 3D7 gC1qR is a PfEMP1 variant characterized by having three of the four domains usually found in DC8 (CIDRα1.1, DBLβ12, DBLγ4/6), differing only in the first DBLα domain.…”

A Unique Virulence Gene Occupies a Principal Position in Immune Evasion by the Malaria Parasite Plasmodium falciparum

“…Nonetheless it appears to be transcriptionally active and highly conserved among geographical isolates, suggesting an important function beyond encoding PfEMP1. The type 3 vars have been shown to be transcribed and translated into uniquely small forms of PfEMP1 [ 58 , 59 ], however whether these proteins function as cytoadhesion molecules and if so, what they bind to has not been determined. These additional conserved var genes therefore share certain characteristics with var2csa .…”

Thevar3genes ofPlasmodium falciparum3D7 strain are differentially expressed in infected erythrocytes

“…The transcription peaked at 16 h post-invasion and terminated immediately afterward (Fig. 2), which was obviously different from the other var genes [19], whose transcription could last until 30–36 h post-invasion [17, 30]. The two genes (PF3D7_0811600 and PF3D7_1361800) were found mainly expressed at 40 and 48 h p.i., respectively (data not shown).…”