Fig. 5

L-homoarginine and diethanolamine as key metabolites in COPD–MS. A Correlation analysis of differential genes with differential metabolites. B Bar graph exhibits the expression of key COPD genes in both groups of patients. C Heatmap depicts the correlation of key COPD genes with differential metabolites. D Bar graph shows the expression of immune checkpoint genes in both groups of patients. E Heatmap demonstrates the correlations of immune checkpoint genes with differential metabolites. *p < 0.05, **p < 0.01, ***p < 0.001