CXCL11 and chronic obstructive pulmonary disease: IC50 values for PF956980 and PF1367550 on IFNγ and IFNγ+TNFα-stimulated release of CXCL9, CXCL10 and CXCL11 from human primary airway epithelial cells from non-smokers, smokers and COPD patients.