CXCL9 and chronic obstructive pulmonary disease: Our own validation of selected model predictions demonstrated that serum protein levels of two CXCR3 chemokines (CXCL9 and CXCL10) are significantly higher in the same COPD cohort used for muscle mRNA profiling, and their levels negatively correlate with the expression of energy metabolism genes in human COPD skeletal muscle (see Figure 6A).