A new approach to identify human red blood cell receptors for Plasmodium parasites

Malaria is one of the most significant public health burdens facing the developing world. While there are several Plasmodium species that can cause malaria in humans, the overwhelming majority of malaria mortality is caused by Plasmodium falciparum parasites. The P. falciparum life cycle is complex, but red blood cell invasion is essential for Plasmodium falciparum survival and pathogenesis, and is therefore a topic of particular interest for the development of novel control and intervention strategies. Invasion involves multiple interactions between parasite ligands and their receptors on human red blood cells, and most of these interactions are thought to have overlapping and redundant roles. However, although multiple P. falciparum invasion ligands are known, in very few cases have their red blood cell receptors been identified. This is in part due to the genetic inaccessibility of the erythrocyte, but also in part because cell surface protein-protein interactions are often of very low affinity, making them hard to identify using standard biochemical approaches. To overcome this, we have used AVEXIS, a systematic protein interaction screening approach designed to detect low affinity extracellular interactions to identify novel red blood cell-parasite interactions. As a first test of this approach, we produced a library of more than 40 recombinant red blood cell surface protein ectodomains, and screened them against the P. falciparum invasion ligand PfRH5. AVEXIS identified basigin/CD147 as the receptor for PfRH5. Basigin (the Oka blood group antigen) has not previously been implicated as playing a role during P. falciparum invasion. Critically, we showed that basigin was essential for parasite entry in every P. falciparum strain tested to date, as invasion in vitro is potently blocked in all parasite strains tested by soluble basigin receptor ectodomains and by receptor-specific monoclonal antibodies. The PfRH5-basigin interaction therefore appears to be an essential and universal entry route for P. falciparum parasites, and is therefore a high priority target for vaccine development. While this work focuses on pathogen-red blood cell interactions, the AVEXIS approach could equally be applied to identify novel extracellular interactions between other cell types within the human blood system.