Hepatocytes, but not HepG2 cells, secrete a “signature set” of cytokines in response to inflammatory stimuli. a, distribution of regression weights in “signals to cytokine” MLR from hepatocyte data. The top 25% of weights (as depicted in Fig. 5, a and b) are shown in blue; the most significant weights, corresponding to signature set cytokines, are shown in green. Distributions for all other MLRs are shown in supplemental Fig. 8. b and c, levels of eight signature set cytokines in hepatocytes and HepG2 cells (as indicated) at t = 0, 3, and 24 h following exposure to TNFα, IL1α, or LPS. Phospho-IκB levels, a measure of IKK activity, are shown above the cytokine data with color coding as in Fig. 1. Absence of the signature set cytokine release in HepG2 cells following exposure to TNFα, IL1α, or LPS is shown by orange shading. VEGFA serves as a control. Norm., normalized; PI3K, phosphatidylinositol 3-kinase.