SCGB1D1 (secretoglobin family 1D member 1), also known as lipophilin A, is a small secreted protein expressed in various tissues, particularly endocrine-responsive organs 1. The protein functions as a component of heterodimeric complexes, notably forming lipophilin AC with SCGB2A1 (lipophilin C) in human tears 2. SCGB1D1 is homologous to rat prostatein, an estramustine-binding protein 2, suggesting it may bind androgens and other lipophilic ligands. Members of the secretoglobin family are typically steroid-regulated and steroid-binding molecules 2. In ocular tissues, SCGB1D1 is expressed in lacrimal glands and other ocular structures alongside androgen receptors, suggesting androgen-regulated expression 3. SCGB1D1 expression is regulated by inflammatory cytokines in the upper airway, though it was not specifically examined for differential regulation across all cytokine conditions in the studies provided 4. In tear proteomics studies, lipophilin A-C levels were significantly decreased in evaporative dry eye disease patients compared to healthy controls, suggesting a protective role in tear film stability 5. The protein's specific ligand-binding properties and potential involvement in tear lipid layer formation remain incompletely characterized.