As shown in Figure 4B, the expression levels of HTR2B (P = 0.0075) and CORIN (P = 0.0049) were significantly lower in COPD lung tissues than in the smoker controls; the expression levels of PLA2G7 (P = 0.0042), SPP1 (P = 0.00032), TM4SF19 (P = 0.0087), and MMP9 (P = 0.0042) were significantly higher in COPD lung tissues than in the smoker controls. Here, MMP9 is linked to chronic obstructive pulmonary disease.