IgG Responses to the Plasmodium falciparum Antigen VAR2CSA in Colombia Are Restricted to Pregnancy and Are Not Induced by Exposure to Plasmodium vivax

Abstract

Clinical immunity to malaria is associated with the acquisition of IgG specific for members of the Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) family of clonally variant antigens on the surface of infected erythrocytes (IEs). The VAR2CSA subtype of PfEMP1 mediates IE binding in the placenta. VAR2CSA-specific IgG is normally acquired only after exposure to placental parasites. However, it was recently reported that men and children from Colombia often have high levels of functional VAR2CSA-specific IgG. This potentially undermines the cur- rent understanding of malaria immunity in pregnant women, and we thus con- ducted a study to assess further the levels of VAR2CSA-specific IgG in pregnant and nonpregnant Colombians. Plasma IgG against two full-length recombinant PfEMP1 proteins (one of the VAR2CSA type and one not) produced in baculovirus- transfected insect cells was detected frequently among Colombian men, children, and pregnant women with acute or previous malaria exposure. In contrast, IgG reac- tivity to a homologous full-length VAR2CSA-type protein expressed in Chinese ham- ster ovary (CHO) cells was low and infrequent among the Colombian plasma sam- ples, as was reactivity to both corresponding native PfEMP1 proteins. Moreover, human and rabbit antibodies specific for Plasmodium vivax Duffy-binding protein (PvDBP), a protein with some homology to PfEMP1, did not react with VAR2CSA- type recombinant or native proteins, although the mouse monoclonal and PvDBP- specific antibody 3D10 was weakly reactive with recombinant proteins expressed in baculovirus-transfected insect cells. Our data indicate that the previously reported Colombian IgG reactivity to recombinant VAR2CSA is not malaria specific and that the acquisition of VAR2CSA-specific IgG is restricted to pregnancy, in Colombia and elsewhere