Binding of human neutrophils to cell-surface anchored Tamm-Horsfall glycoprotein in tubulointerstitial nephritis

Background. Human Tamm-Horsfall glycoprotein (T-H) is a glycosylphosphatidy linositol-anchored protein exposed at the surface of distal nephron cells, and urinary T-H is the released soluble counterpart. The latter has been im plicated in tubulointerstitial nephritis, and the proinflammatory potential has been related to its ability to bind in vitro human neutrophils (PMNs). We have examined the conditions required for the binding of neutrophils to cell-surface anchored T-H and the consequent effects. Methods. A HeLa cell-line derivative permanently transformed with human T-H cDNA and expressing T-H at the cell surface was used throughout the study. The adhesion of PMNs to cells expressing T-H was analyzed by immunofluores cence microscopy before and after the opsonization of cells with anti-T-H a ntibodies. The oxidative burst induced by adhesion of PMNs to the cells was determined by the activation of myeloperoxidase. Quantitative and qualitat ive changes in the release of T-H under the adhesion of activated PMNs were determined by dot-blot and Western blot analysis. Results. No binding of neutrophils to cell-surface-anchored T-H was observe d. On the contrary, the opsonization of cells with anti-T-H antibodies resu lted in a dramatic adhesion of neutrophils. Such an adhesion induced the ox idative burst of PMNs and a large increment in the release of T-H, as well as the release of the slightly faster migrating T-H form, which is normally retained intracellularly. Conclusions. These results support the notion that, after the autoimmune re sponse, the adhesion of neutrophils to cell-surface T-H contributes to the pathogenesis of tubulointerstitial nephritis, favoring a further accumulati on of T-H in the interstitium and inducing the loss of cell integrity via r eactive oxygen metabolites generated by activated neutrophils.