Immunohistochemical detection of hypochlorite-modified proteins in glomeruli of human membranous glomerulonephritis

Abstract

A proposed analogy between atherosclerosis and glomerulosclerosis suggests that factors that contribute to the development of atherosclerosis, ie, oxidatively modified (lipo)proteins, may also participate in glomerular injury. Although the nature of the in vivo oxidants has not been clearly identified, increasing evidence suggested the myeloperoxidase (MPO)-H2O2-halide system to be responsible for the damage observed in leukocyte-dependent glomerulonephritis. MPO, a heme protein secreted by activated phagocytes, may generate modified/oxidized proteins in vivo via intermediate formation of hypochlorous acid (HOCI)/hypochlorite. HOCI, a reactive oxygen species and powerful oxidant, can convert (lipo)proteins into atherogenic forms in vitro and in vivo. Here we demonstrate the presence of HOCI-modified proteins in glomeruli of patients with membranous glomerulonephritis using monoclonal antibodies that do not cross-react with other oxidative modifications. Immunostaining for HOCI-modified epitopes in human minimal change glomerulopathy revealed glomeruli that were unreactive, although the number of MPO-positive cells/glomerulus was slightly increased in comparison to controls. In contrast to minimal change glomerulopathy, a pronounced infiltration of mononuclear cells/glomerulus in membranoproliferative glomerulonephritis is in line with pronounced staining for HOCI-modified epitopes. Immunostaining was detected in intracapillary cells and immune complex deposits within the glomerular basement membrane. In human membranous glomerulonephritis (Stages I to III), staining for HOCI-modified proteins was localized at the basement membrane and podocytes. Staining of serial sections revealed colocalization of HOCI-modified epitopes and MPO in glomerular peripheral basement membranes. Subsequently, tubulointerstitial staining for HOCI-modified epitopes was observed in foam cells at the border of the cytoplasm and in damaged tubular epithelia in focal advanced chronic lesions. Our results indicate that oxidative modification of the basement membrane structure by phagocytederived HOCI may be of importance for glomerular defects. The observed colocalization of HOCI-modified proteins and MPO in podocytes and adjacent basement membranes strengthens the assumption that the MPO-H2O2-halide system contributes to glomerular dysfunction in patients with membranous glomerulonephritis.