A role for IL-33 in human type 2–driven chronic airway disease was highlighted by genome-wide association studies linking IL33 and IL1RL1/ST2 with asthma (4–6) and increased IL-33 in serum, sputum, or tissue from patients with asthma (7, 8) and patients with chronic obstructive pulmonary disease (COPD) (9–11). Here, IL1RL1 is linked to asthma.