CXCL9 and chronic obstructive pulmonary disease: Its role in chronic respiratory diseases remains unclear, with conflicting evidence suggesting it may reflect steroid-responsive inflammation in interstitial lung disease (ILD) but correlate with worse function in chronic obstructive pulmonary disease (COPD).<h4>Methods</h4>Serum levels of CXCL9, KL-6, SP-A, and CRP were measured in 83 ILD patients (with paired samples before and after treatment), 94 COPD patients, and 100 healthy controls (50 smokers and 50 non-smokers).