Strain-specificity of receptor antagonism. CXCR4 (A., G.) and CD134 (B., H.) were quantified on CLL-CD134 (A., B) and MYA-1 (G., H.) cells by flow cytometry. Bound anti-CXCR4 antibody was detected with PE-anti-mouse IgG. Histograms show 10,000 events collected in LIST mode. Inhibitory activity of AMD3100 (C., E., I., K) and soluble Fc-CD134 (D., F., J., L.) were then compared on CLL-CD134 (C., D., E., F.) and MYA-1 (I., J., K., L.) cells. (C., D., I., J.) Luciferase activity versus antagonist concentration, (E., F., K., L.) Infectivity (percent infection relative to no antagonist) versus antagonist concentration. Each point represent the mean +/− standard error (n=3).