Unlike the case in Asia and Latin America, <i>Plasmodium vivax</i> infections are rare in sub-Saharan Africa due to the absence of the Duffy blood group antigen (Duffy antigen), the only known erythrocyte receptor for the <i>P. vivax</i> merozoite invasion ligand, Duffy binding protein 1 (DBP1).However, <i>P. vivax</i> infections have been documented in Duffy-negative individuals throughout Africa, suggesting that <i>P. vivax</i> may use ligands other than DBP1 to invade Duffy-negative erythrocytes through other receptors.To identify potential <i>P. vivax</i> ligands, we compared parasite gene expression in <i>Saimiri</i> and <i>Aotus</i> monkey erythrocytes infected with <i>P. vivax</i> Salvador I (Sal I).
RH5 is a leading subunit vaccine candidate because anti-RH5 antibodies inhibit parasite growth and the interaction with its erythrocyte receptor basigin is essential for invasion.
They both share homology of domain structure, including the binding region (Region II), which consists of two homologous F1 and F2 domains and is responsible for ligand-erythrocyte receptor interaction during merozoite invasion.
The molecular mechanism(s) responsible for these host restrictions are not understood, although the interaction between the parasite blood-stage invasion ligand EBA175 and the host erythrocyte receptor Glycophorin-A (GYPA) has been implicated previously.
The protease-resistant properties of the erythrocyte receptor suggests that it is not glycophorin A or C. Additionally, analysis of mutant erythrocytes from humans has shown that EBA140 does not bind glycophorin B. Interestingly, we have identified a parasite line that lacks the eba140 gene, suggesting that this protein is not essential for in vitro invasion.