Induction of endothelial cell monolayer permeability by tumor conditioned supernatant in an IL-1-dependent manner. Permeability across functional endothelial cell monolayers was determined by measuring absorbance at 620 nm 1 hour following supernatant exposure. Induction of permeability by SMEL (A) and H2030, a lung non-small-cell carcinoma, (B) was completely or partially blocked by co incubation with 10 mg/mL IL-1Ra. PMEL did not induce permeability under identical experimental conditions (C). Tumor necrosis factor (TNF) at 10 ng/mL served as positive control. Columns, mean; bars, SE.