Secreted cytokine-like protein (By similarity). Binds to the scavenger receptor MARCO (By similarity). Can also bind to pathogens including the Gram-positive bacterium L.monocytogenes, the Gram-negative bacterium P.aeruginosa, and yeast (By similarity). Strongly inhibits phospholipase A2 (PLA2G1B) activity (PubMed:24213919). Seems to have anti-inflammatory effects in respiratory epithelium (PubMed:16456148, PubMed:25242865). Also has anti-fibrotic activity in lung (PubMed:24213919, PubMed:26559674). May play a role in fetal lung development and maturation (PubMed:18535256). Promotes branching morphogenesis during early stages of lung development (PubMed:18535256). In the pituitary, may inhibit production of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) (PubMed:24514953). Homodimer; disulfide-linked (PubMed:11682631, PubMed:24213919). Monomer (PubMed:11682631, PubMed:24213919). Interacts with APOA1 (By similarity). Highly expressed in lung where it localizes to epithelial cells of the trachea, bronchus and bronchioles (at protein level) (PubMed:11682631, PubMed:12406855, PubMed:12175512, PubMed:25242865). Expressed in club/Clara cells of the bronchioles (PubMed:12406855). Also detected in the anterior and posterior lobes of the pituitary gland where it may localize to gonadotropic cells (at protein level) (PubMed:24514953). Not detected in other tissues tested (PubMed:11682631, PubMed:12175512). Detected in the pituitary gland from postnatal day 1 onwards (at protein level) (PubMed:24514953). Weakly expressed in embryonic lung at stages 11.5 dpc and 12.5 dpc (PubMed:11682631, PubMed:18535256). Seems to localize most strongly to the growing tips of bronchi at stage 13.5 dpc (PubMed:18535256). Highly expressed in developing lung at stages 16.5 dpc and 18.5 dpc, where it localizes to airway epithelia (PubMed:11682631, PubMed:12406855, PubMed:12175512, PubMed:24514953). During gestation, detected in the mammary gland at 6.5 days post coitum (dpc), but expression declines at 8.5 dpc and is absent at later stages (PubMed:12175512). Viable and fertile, with no gross abnormalities. Lung tissue appears normal (PubMed:25242865). In a C57BL/6NCr strain background, animals show a mild increase in ovalbumin-induced inflammatory response in lung (PubMed:25242865). However, in a mixed genetic background, there is a reduced ovalbumin-induced inflammatory response, possibly due to the presence of modifier genes (PubMed:25242865). Animals have a more severe response to bleomycin-induced pulmonary fibrosis characterized by increased weight loss, more extensive fibrosis in lung tissue, increased expression of collagen genes, higher numbers of lymphocyte, monocyte and neutrophil cells in bronchoalveolar lavage fluid, and increased cytokine levels (PubMed:26559674). Major isoform. Belongs to the secretoglobin family. UGRP subfamily.