Then, drawing from previous evidence that Th2-predominant immune response may play an important role in the development of lung fibrosis in chronic HP, we also analyzed serum levels of CXCL9 (Th1 chemokine), CCL17 (Th2 chemokine), and Krebs von den Lungen 6 (KL-6) [9]. This evidence concerns the gene CXCL9 and pulmonary fibrosis.