The mechanism of the emphysema is complex, and matrix metalloproteinases, particularly MMP-9 and MMP-12, are of interest; activation of the IL-17 → MCP-1(Ccl-2) → MMP-9 → MMP-12 axis appears to be critical for the formation of emphysema [86,87,88]. The gene discussed is IL17A; the disease is pulmonary emphysema.