Molecular mechanism for switching of P.falciparum invasion pathways into human erythrocytes

The malaria parasite, Plasmodium falciparum, exploits multiple ligand-receptor interactions, called invasion pathways, to invade the host erythrocyte. Strains of P.falciparum vary in their dependency on sialated red cell receptors for invasion. We show that switching from sialic acid-dependent to –independent invasion is reversible and depends on parasite ligand utilisation. Expression of P.falciparum reticulocyte-binding like homologue 4 (PfRh4) correlates with sialic acid-independent invasion and PfRh4 is essential for switching invasion pathways. Differential activation of PfRh4 represents a novel mechanism of invasion pathway control and provides P.falciparum with exquisite adaptability in the face of erythrocyte receptor polymorphisms and host immune responses. Keywords: Plasmodium falciparum, erythrocyte invasion, invasion pathways, EBA175, Rh4 Experiment contains no replication. There are three genotypes: wildtype W2mef parasites, a cloned variant that can invade via a sialic acid independent pathway, and a parasite in which EBA175 has been knocked out and which also invades via a sialic acid independent pathway.