Human IL-10, human IL-6, and vIL-6 binding to BCBL-1 and BC-1 cells. Biotinylated human IL-10 (1.5 μg/mL), human IL-6 (1.5 μg/mL), soybean trypsin inhibitor (1.5 μg/mL), vIL-6 (MBP-vIL-6; 1.5 μg/mL), or MBP (1.5 μg/mL) was incubated with BCBL-1 and BC-1 cells. Cell-bound protein was shown by the addition of avidin-fluorescein (10 μg/mL). After washing, surface fluorescence was evaluated by FACScan analysis. Unshaded histograms reflect binding from control biotinylated control proteins (soybean trypsin inhibitor or MBP).