Constitutive IL-6 expression by NRP-152 & NRP-154 cells. Confluent cells were harvested, fixed, and permeabilized as described in Materials & Methods. They were stained with goat anti-rat IL-6, then with fluorescent anti-goat Ig. Cells were analyzed on a FACScan for fluorescence in FL2. A, NRP-152 cells. B, NRP-154 cells. In both histograms, green = fluorescent anti-goat Ig only; purple = goat anti-rat IL-6 plus fluorescent anti-goat Ig. KS analysis revealed that the fluorescence intensity of the NRP-154 cells in the second peak in panel B were 3 to 5 times the fluorescence intensity of the control-stained cells (green peak in panel B; p < 0.01). A histogram from 1 experiment is shown here.