Clara cell protein or urinary protein 1 is a homodimeric protein of 16 kD and is secreted predominantly by Clara cells in terminal bronchioles and from puberty on in the male urogenital tract. CC16 is formed by two chains, each with a molecular weight of 7.9 kD. CC16 occurs in very high concentrations in respiratory tract derived fluids such as sputum or bronchoalveolar lavage fluid. CC16 occurs also in urogenital secretions, such as amniotic fluid, urine and semen. The protein difusses passively into serum. CC16 behaves like an anti-cytokine by downregulating the production of IFN-gamma, IL-1 and TNF-alpha by stimulated leukocytes. Besides this, CC16 reduces the antiviral activity and the augmentation of phagocytosis induced by IFN-gamma.Synonyms: Urinary protein 1