CD98 is a Plasmodium vivax receptor for human reticulocytes

Background: Plasmodium vivax, a pathogen of global importance, has long been known to have a strict preference to invade immature red blood cells. We have recently demonstrated that P. vivax invades preferentially CD71+ (Transferrin receptor) reticulocytes. P. vivax reticulocyte binding protein (PvRBP) family is believed to mediate specific invasion of reticulocytes by P. vivax. The invasion of vivax is also DARC (Duffy antigen/chemokine receptor) dependent and involved the interaction with DBP (Duffy binding protein) at the surface of vivax merozoites. Interestingly, DARC is also expressed by mature red blood cells (normocytes) therefore the presence of this receptor is not responsible for reticulocyte tropism of P. vivax. Materials and Methods: The strategy we adopted was based on a differential proteomic screen of CD71+ versus CD71- erythrocyte ghost membranes to determine dynamic changes on surface protein composition and to identify abundant reticulocyte proteins. The criteria we adopted to select candidate reticulocyte-specific receptors were: a) expression and presence on the immature reticulocytes but not on the normocytes, and b) insensitivity to trypsin treatment. Results: Two surface proteins displayed remarkable a massive fold-change reduction in their expression levels between CD71+ and CD71- erythrocytes, namely CD71 (ca. 2.67-fold) and CD98 (ca. 1.98-fold), while all others were less than a 2-fold change. Of these two proteins, only CD98 proved resistant to trypsin treatment. CD98 (also known as 4F2hc), is the heavy chain component of the Large neutral Amino acid Transporter (LAT) complex that is exposed to outside of the reticulocyte surface membrane. Anti-CD98 antibodies significantly abrogated the invasion of P. vivax merozoites into CD71+ reticulocytes. Binding assays using these cells with CD71+ versus CD71- erythrocytes identified fragments encoded by two genes (RBP2a and RBP2b) that mediated strong binding to CD71+ reticulocytes. As expected binding of cells transfected with the PvRBP2a to reticulocytes was fully abrogated by the presence of two distinct anti-PvRBP2a mouse monoclonal antibodies. Conclusions: CD98 on the reticulocyte and Plasmodium vivax PvRBP2a form a receptor-ligand pair implicated in the parasite’s erythrocyte selection. This significantly reinforces the potential of this parasite protein as a vaccine candidate against vivax malaria.