Chemokine Class Differences in Binding to the Duffy Antigen-Erythrocyte Chemokine Receptor

The Duffy blood group antigen-erythrocyte chemokine receptor has been shown to bind to chemokines of both the C-X-C and C-C classes and to the malarial parasites Plasmodium vivax and Plasmodium knowlesi. We performed experiments to evaluate the binding properties of this receptor for the newly appreciated "C" and "non-ELR C-X-C" classes of chemokines. Binding to mouse erythrocytes was also evaluated for the first time. Whereas ELR C-X-C and C-C chemokines bound to human erythrocytes with high affinity, differences in the ability of non-ELR chemokines to act as competitive inhibitors were noted. While non-ELR chemokines were unable to displace C-X-C chemokines on human cells, they exhibited a low affinity interaction with the C-C chemokine binding site. The newly discovered C chemokine, lymphotactin, was unable to displace either C-X-C or C-C chemokines. On mouse erythrocytes, non-ELR chemokines exhibited a low affinity for both the C-X-C and C-C chemokines binding sites; again lymphotactin failed to bind. Binding competition studies using an anti-Duffy monoclonal antibody and chemokines suggested a common binding domain. These data show that the chemokine superfamily has at least four functional subdivisions, each interacting differently with the Duffy antigen-erythrocyte chemokine receptor. In addition the chemokine binding function is conserved between mouse and man. Unlike other proteins in the superfamily C and non-ELR C-X-C chemokines do not efficiently bind red blood cells, thus their role may not require clearance from circulation.