Identifying targets of protective antibodies against severe malaria in Papua, Indonesia using locally expressed domains of Plasmodium falciparum Erythrocyte Membrane Protein 1.

Abstract

Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1), a diverse family of multi-domain proteins expressed on the surface of malaria-infected erythrocytes, is an important target of protective immunity against malaria. Our group recently studied transcription of the var genes encoding PfEMP1 in individuals from Papua, Indonesia with severe or uncomplicated malaria. We cloned and expressed domains from 32 PfEMP1s including 22 that were upregulated in severe malaria and 10 that were upregulated in uncomplicated malaria, using a wheat germ cell-free expression system. We used Luminex technology to measure IgG antibodies to these 32 domains and control proteins in 63 individuals (11 children). At presentation to hospital, levels of antibodies to PfEMP1 domains were either higher in uncomplicated malaria or were not significantly different between groups. Using principal components analysis, antibodies to three of 32 domains were highly discriminatory between groups. These included two domains upregulated in severe malaria, a DBLβ13 domain and a CIDRα1.6 domain (which has been previously implicated in severe malaria pathogenesis), and a DBLδ domain that was upregulated in uncomplicated malaria. Antibody to control non-PfEMP1 antigens did not differ with disease severity. Antibodies to PfEMP1 domains differ with malaria severity. Lack of antibodies to locally expressed PfEMP1 types, including both domains previously associated with severe malaria and newly identified targets, may in part explain malaria severity in Papuan adults. Importance Severe Plasmodium falciparum malaria kills many African children, and lack of antibody immunity predisposes to severe disease. A critical antibody target is the P. falciparum erythrocyte membrane 1 (PfEMP1) family of multidomain proteins, which are expressed on the infected erythrocyte surface and mediate parasite sequestration in deep organs. We previously identified var genes encoding PfEMP1 that were differentially expressed between severe and uncomplicated malaria in Papua, Indonesia. Here, we have expressed domains from 32 of these PfEMP1s and measured IgG antibody responses to them in Papuan adults and children. Using Principal Component Analysis, IgG antibodies to three domains distinguished between severe and uncomplicated malaria and were higher in uncomplicated malaria. Domains included CIDRα1.6, implicated in severe malaria; a DBLβ13 domain; and a DBLδ domain of unknown function. Immunity to locally relevant PfEMP1 domains may protect from severe malaria. Targets of immunity show important overlap between Asian adults and African children.