(A) Functional response of CCR5 to various CC-chemokines. The functional activity of chemokines able to bind to CCR5 was assayed by using a cell line coexpressing the receptor together with G_α16 and apoaequorin. Light emission resulting from the activation of the apoaequorin-coelenterazine complex in the presence of intracellular calcium was recorded in a luminometer. The results were analyzed by the Graphpad Prism software, using a single-site model, and the data were normalized for basal luminescence (0%) and maximal luminescence in the presence of 200 nmol/L MIP-1β (100%). All points were run in duplicate (error bars: S.E.M.). The displayed curves represent a typical experiment out of three performed independently. (B) Inhibition of the MIP-1β functional response by MCP-3. The antagonistic activity of MCP-3 was measured by preincubating the cells for 1 minute with MCP-3, before the addition of 1 nmol/L MIP-1β, and recording of luminescence. All points were run in triplicate (error bars: S.E.M.), and the results are representative of two independent experiments.