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). Here, CHI3L1 is linked to Hermansky-Pudlak syndrome.