Cytokines play a critical role in the pathobiologic processes of COPD, including altered innate immune response, chronic inflammation, emphysema, and small airway fibrosis.1 Proinflammatory cytokines of potential importance include tumor necrosis factor-α, interferon-γ, IL-1β, IL-17, and IL-6. Here, IL17A is linked to chronic obstructive pulmonary disease.