vCXCL1 or ELR-positive CXC chemokines induced chemotaxis of L1.2 cells stably expressing either CXCR1 or CXCR2, but not of naïve L1.2 cells. A, chemotactic activities of L1.2 cells stably transfected with CXCR1 or CXCR2 toward vCXCL1 or different endogenous ELR-positive or negative chemokines. □, vCXCL1; ■, CXCL8/IL-8; ●, CXCL6/GCP-2; ▴, CXCL7/NAP-2; ▾, CXCL5/ENA-78; ▵, CXCL1/GROα; ▿, CXCL2/GROβ; ◇, CXCL3/GROγ; *, CXCL11/I-TAC. The insets show the chemotactic activities of low efficacy ligands and the negative control on more appropriate scales. The figure shows one representative assay with S.E. as indicated (n = 3 for vCXCL1 and CXCL8 and n = 2 for the rest of the ligands). B, chemotactic activities of naïve L1.2 cells toward vCXCL1 (□) and CXCL12/SDF-1α (×). The inset shows the chemotactic activity of vCXCL1 (□) on a scale from 0 to 50. The data show one representative assay with S.E. as indicated (n = 2).