CCL2 and chronic obstructive pulmonary disease: In the PPI network of the 21 genes related to the response to steroid hormones in COPD and NR3C1, the top nine hub genes with the highest criticality were EGFR, FOS, SPP1, FN1, CCL2, IL1B, NQ O 1, BMP4, and C3 (Figure 5B).