Asthmatic airway smooth muscle (ASM) expresses interferon-␥-inducible protein-10 (CXCL10), a chemokine known to mediate mast cell migration into ASM bundles that has been reported in the airways of asthmatic patients. CXCL10 is elevated in patients suffering from viral exacerbations of asthma and in patients with chronic obstructive pulmonary disease (COPD), diseases in which corticosteroids are largely ineffective. IFN␥ and TNF␣ synergistically induce CXCL10 release from human ASM cells in a steroid-insensitive manner, via an as yet undefined mechanism. We report that TNF␣ activates the classical NF-B (nuclear factor B) pathway, whereas IFN␥ activates JAK2/STAT-1␣ and that inhibition of the JAK/STAT pathway is more effective in abrogating CXCL10 release than the steroid fluticasone. The synergy observed with TNF␣ and IFN␥ together, however, did not lie at the level of NF-B activation, STAT-1␣ phosphorylation, or in vivo binding of these transcription factors to the CXCL10 promoter. Stimulation of human ASM cells with TNF␣ and IFN␥ induced histone H4 but not histone H3 acetylation at the CXCL10 promoter, although no synergism was observed when both cytokines were combined. We show, however, that TNF␣ and IFN␥ exert a synergistic effect on the recruitment of CREB-binding protein (CBP) to the CXCL10, which is accompanied by increased RNA polymerase II. Our results provide evidence that synergism between TNF␣ and IFN␥ lies at the level of coactivator recruitment in human ASM and suggest that inhibition of JAK/STAT signaling may be of therapeutic benefit in steroid-resistant airway disease.Lung diseases such as asthma and COPD 2 cause significant morbidity and mortality in Western societies. 5-10% of the asthmatic population are unresponsive to corticosteroids, the mainstay for asthma therapy, and patients with COPD are treated ineffectively with steroids. Additionally, viral exacerbations of asthma are a major cause of morbidity and mortality associated with asthma and are relatively unresponsive to steroids (1, 2).CXCL10, a member of the CXC chemokine subfamily, is a potent chemoattractant for mast cells and T lymphocytes, cells implicated in the pathophysiology of asthma and COPD. CXCL10 is elevated in the airways of asthmatic patients and has been implicated in mast cell migration to the ASM bundles (3). CXCL10 also is elevated in the bronchial mucosa and broncho alveolar lavage (BAL) fluid of subjects with moderate/severe asthma, which is largely steroid-resistant (4). Enhanced CXCL10 secretion also has been demonstrated in COPD (5-7), and more recently, it has been reported that serum CXCL10 levels are increased to a greater extent in asthmatics with acute virus-induced asthma compared with nonvirus-induced acute asthma, and increased levels are predictive of virus-induced asthma exacerbations (8). CXCL10 is released in response to IFN␥ or TNF␣ from a number of inflammatory cell types (6, 9 -12), and several reports also have shown that TNF␣ and IFN␥ synergistically enhance CXCL10 release (13-16). Given the he...