TNFR1 and TNFR2 are expressed on native human ASM but activation of TNFR1 mediates ICAM-1 expression in human ASM cells. TNFR1 and TNFR2 are expressed on native human ASM but activation of TNFR1 mediates ICAM-1 expression in human ASM cells. A, cells were incubated with 30 μg/ml htr-9 or 30 μg/ml utr-1 (anti-TNFRp75) in the presence or absence of TNFα (10 ng/ml) for 4 h. ICAM-1 expression was assessed as described inMaterials and Methods. Values shown are mean ± S.E. (n = 6 separate experiments). **P < .01 and #P< .01 compared with untreated cells; NS not significant from cells treated with cytokine alone. B, sections of fresh tracheal tissues were incubated with no primary antibody (A), 10 μg/ml antibody against TNFR2 (B) or TNFR1 (C). Cell surface expression of TNFα receptors was assessed as described in Materials and Methods. Arrow locates the smooth muscle positively stained for TNFα receptors. This is a representative photomicrograph of tracheal sections from three donors showing identical patterns of TNFR expression. Yassine Amrani et al. Mol Pharmacol 2000;58:237-245 The American Society for Pharmacology and Experimental Therapeutics