CHI3L1 and idiopathic pulmonary fibrosis: In patients with HPS pulmonary fibrosis (HPSPF) and idiopathic pulmonary fibrosis (IPF), high serum and lung levels of CHI3L1 are associated with disease progression and with alternatively activated circulating monocytes and macrophages, independent of its ability to bind and degrade chitin (16, 29).