Altered glycosylation of Tamm-Horsfall glycoprotein derived from renal allograft recipients leads to changes in its biological function

BackgroundHuman urinary Tamm-Horsfall glycoprotein (THP) is a pleotropic protein that binds different cytokines and stimulates various immunocompetent cells. It is unclear whether these important functions of THP are altered in renal transplant patients.MethodsWe purified THPs from normal individuals (N-THP) and renal transplant patients receiving potent immunosuppressants (R-THP). The carbohydrate (CHO) compositions of THPs were probed by lectin-blotting and lectin-binding ELISA. The functions of THP were assessed by immune cell-stimulation as well as C1q, IL-1β, IL-8 and TNF-α-binding assays. The roles of CHO moieties in THPs were analyzed using CHO-degrading enzyme digestion.ResultsCompared to that of N-THP, the binding capacity of R-THP to Maackia amurensis, Galanthus nivalis and Datura stamonium decreased, indicating that R-THP contained lesser amount of Siaα(2,3)Gal/GalNAc, mannose residues, and β(1,4)GlcNAc, but not GlcNAc/branched mannose. The binding capacity of R-THP to complement C1q and tumor necrosis factor (TNF)-α was also decreased. The stimulating effect of R-THP on mononuclear cell (MNC) proliferation and polymorphonuclear neutrophil (PMN) phagocytosis was less potent than that of N-THP. We found that the defective MNC-stimulation by R-THP was due to impaired NF-κB p52 nuclear translocation. The cell-stimulating effects of N- and R-THP could be abolished by digesting them with CHO-degrading enzymes, β-galactosidase and neuraminidase. Interestingly, a potent apoptosis-inducing effect of R-THP on MNC and PMN was noted.ConclusionsR-THP is not only modified in glycosylation but bears an apoptosis-inducing capacity on MNC and PMN, leading to an impaired immune function in renal transplant patients.