Th1 cytokines tnf-α and ifn-γ promote corticosteroid resistance in developing human airway smooth muscle

Corticosteroids (CSs) are commonly used to manage wheezing and asthma in pediatric populations. Although corticosteroids are effective in alleviating airway diseases, some children with more moderate-severe asthma phenotypes show CS resistance and exhibit significant airflow obstruction, persistent inflammation, and more frequent exacerbations. Previous studies have demonstrated that Th1 cytokines, such as TNF-α and IFN-γ, promote CS resistance in adult human airway smooth muscle (ASM). In the present study, using a human fetal ASM cell model, we tested the hypothesis that TNF-α and IFN-γ induces CS resistance. In contrast to TNF-α and IFN-γ alone, the combination of TNF-α and IFN-γ blunted the ability of fluticasone propionate (FP) to reduce expression of the chemokines CCL5 and CXCL10 despite expression of key anti-inflammatory glucocorticoid receptor target genes being largely unaffected by TNF-α and IFN-γ. Expression of the NF-κB subunit p65 and phosphorylation of Stat1 were elevated in cells treated with TNF-α and IFN-γ, an effect that remained in the presence of FP. siRNA knockdown studies demonstrated the effects of TNF-α and IFN-γ on increased p65 are mediated by Stat1, a transcription factor activated by IFN- γ. Expression of TNFAIP3, a negative regulator of NF-κB activity, was not altered by TNF-α and IFN-γ. However, the effects of TNF-α and IFN-γ were partially reduced by overexpression of TNFAIP3 but did not influence p65 expression. Together, these data suggest that IFN- γ augments the effects of TNF- α on chemokines by enhancing expression of key inflammatory pathways in the presence of CS. Interactions between TNF-α and IFN-γ -mediated pathways may promote inflammation in asthmatic children resistant to CSs.