[Tamm-Horsfall protein]

Tamm-Horsfall (TH) glycoprotein is a major protein of normal urine and is the primary component of waxy nephron casts. Tamm-Horsfall protein is of renal origin and has been localized in the thick ascending limb of the loop of Henle and in the distal convoluted tubule. Its physicochemical properties are characterized by its tendency to form aggregates in the presence of increasing concentrations of NaCl or H+. The primary structure of Tamm-Horsfall protein has been characterized and was shown to be identical to uromodulin, a glycoprotein purified from the urine of pregnant women and which has immunosuppressive properties. TH protein probably has a different glycosylation since it does not have the same immunosuppressive properties as uromodulin. TH protein is anchored to the cytoplasmic membrane via a phosphatidyl-inositol group, and could be secreted in urine after cleavage by a specific phospholipase. The role of TH protein in physiological and pathological states, as well as its regulation, are still unknown. Recently, the main protein secreted in the rat pancreatic juice has been cloned (GP2). It is 88% homologous to TH protein, some of GP2 properties are the same as TH properties. The existence of a new family of proteins and the search for new homologous proteins will probably help to understand the role of TH protein.