CCL17 and hypersensitivity pneumonitis: The CXCL9, CCL17, and KL-6 serum levels were significantly higher in the patients with chronic bird-related HP than in the healthy volunteers (CXCL9; chronic bird-related HP vs. HV, 19.3 (13.2–35.6) vs. 10.5 (7.6–15.6) pg/ml, P < 0.001.