Invasion of erythrocytes by the virulent malaria parasite Plasmodium falciparum is an essential stage of the parasite life cycle that relies on multiple ligand-receptor interactions. P. falciparum causes severe disease in the human host due is its ability to evade host immune responses and invade erythrocytes of varying receptor repertoires. While many of the parasite proteins that make up these ligand-receptor interactions are known and well characterized, both the role of polymorphism within these proteins and the erythrocyte receptors to which they bind remain largely unknown. The aim of this work is to determine the role of both host and parasite determinants of erythrocyte invasion, and the role of naturally arising polymorphism, using novel genetic approaches.

To determine the role of a naturally occurring polymorphism in the important invasion ligand PfRh2b, in alternative invasion pathway utilization and evasion of inhibitory immune responses, we generated transgenic parasites that express the PfRh2b deletion in an isogenic background. We observe that the PfRh2b deletion does not have a role in alternative invasion pathway usage, but rather confers a growth advantage to the parasite and facilitates escape from antibody-mediated inhibition of erythrocyte invasion.

While many of the parasite determinants of erythrocyte invasion are known, few studies have addressed the erythrocyte contribution to host-parasite interactions, largely because the absence of a nucleus in the terminally differentiated erythrocyte precludes direct genetic manipulation. To address this challenge in the field, we developed a system that combines in vitro culture of erythrocytes with lentiviral transduction of hematopoietic stem cell precursors to knock-down expression of erythrocyte receptors in the mature erythrocyte. We find that reducing glycophorin A on the surface of the erythrocyte inhibits invasion of the sialic acid dependent parasite W2Mef, however strains which do not rely on EBA-175 for invasion are unaffected. This data confirms a role for the erythrocyte receptor glyocphorin A in alternative invasion pathway utilization. In striking contrast, we find that knock-down of basigin, the recently identified receptor for PfRh5, results in dramatic inhibition of both sialic acid dependent and independent parasites, implying that basigin may be an essential receptor for P. falciparum invasion.