Binding of RANTES, MCP-1, MCP-3, and MIP-1alpha to cells in human skin

Based on their ability to induce leukocyte chemotaxis and adhesion to endothelial cells (ECs), chemokines have been implicated in driving inflammatory leukocyte emigration. Recently, it was suggested that chemokines can accomplish their pro-emigratory role more effectively while being bound to the luminal surface of the ECs. Previously, such binding was demonstrated in situ in human skin for the prototype alpha-chemokine interleukin (IL)-8. Here we used an in situ binding assay to investigate the binding characteristics of several beta-chemokines in intact human skin. RANTES, MCP-1, and MCP-3 bound, similar to IL-8, in a specific saturable manner to the ECs of venules and small veins but not arteries or capillaries. RANTES inhibited MCP-1 and MCP-3 binding and vice versa, indicating that the EC binding sites are shared among these beta-chemokines; moreover, IL-8 and RANTES cross-competed for each other's binding, suggesting that the same chemokine binding sites are used by members of alpha- and beta-chemokine subfamilies. Conversely, MIP-1alpha did not bind to the ECs and did not compete for binding of RANTES. Analogous to IL-8, all of the tested beta-chemokines bound to the resident dermal cells. As a novel aspect of chemokine interaction with cells in normal skin, we observed specific, saturable binding of RANTES, MCP-1, and MCP-3 but not MIP-1alpha or IL-8 to the ECs of dermal afferent lymphatic vessels. RANTES, MCP-1, and MCP-3 also cross-competed for each other's binding to lymphatics, suggesting a common binding site with a novel chemokine binding profile. We suggest that the chemokine binding to the ECs of lymphatics may be involved in the process of leukocyte entry into the afferent lymphatic vessels.