IL17A and chronic obstructive pulmonary disease: Specifically, a higher gene signature was associated with lower FEV1 expressed as a percentage of the predicted value (FEV1% predicted) across all participants (1 unit increase in the IL-17 signature is associated with a 12-ml decrease in FEV1, P = 1.40 × 10–5) and among only COPD participants (associated with a 5.5-ml decrease in FEV1, P = 0.04), suggesting an association with increasing COPD severity (Figure 4B).