As shown in Figure 3C, 100 hub genes (e.g., MAPK3, MAPK14, PTGS2, ICAM1, CXCL8, JUN, and IL17A) were extracted from a PPI network of 1180 COPD genes based on their degree value, and then their immune system processes were analyzed. Here, ICAM1 is linked to chronic obstructive pulmonary disease.