IL-6 receptor is expressed on untreated NRP-152 & NRP-154 cells. Confluent cells were removed with citrate-saline buffer and stained with 2 μg/106 cells goat anti-IL-6 receptor (R&D Systems). Fluorescent anti-goat Ig was then added. Fluorescence in FL2 was analyzed using a FACScan. A, NRP-152 cells. The blue line is the fluorescence control; the red line is the fluorescence due to the IL-6 receptor on the cells. The anti-IL-6 receptor-stained cells were 30 times as fluorescent as the control stained cells (p < 0.001 by KS statistics). B, NRP-154 cells. The green line is the fluorescence control; the purple curve is the IL-6 receptor on the cells. The anti-IL-6 receptor-stained cells (second red peak) were 10 times brighter than the control-stained cells (green peak; p < 0.001 by KS statistics). The first red peak was comprised of cells that did not stain positive for the IL-6 receptor.