Intrarenal synthesis of IL‐6 in IgA nephropathy

Summary: Recent in vitro studies have shown the synthesis of interleukin‐6 (IL‐6) in glomerular mesangial and epithelial cells, and suggested the involvement of IL‐6 in mesangial proliferative glomerulonephritis. However, the expression site of IL‐6 mRNA in renal tissue of IgA nephropathy (IgAN), the most common chronic mesangial proliferative glomerulonephritis, remains obscure. to localize IL‐6 mRNA in renal biopsy specimens of IgAN, we used nonradioactive in situ hybridization (ISH) developed in our laboratory, sensitive in detecting individual cells positive for a specific mRNA. In some sections, periodic acid‐Schiff staining was performed after ISH in order to identify the topographical relation between IL‐6 mRNA positive cells and glomerular basement membrane and mesangial area. In situ hybridization for IL‐6 mRNA and immunohistochemistry for CD3 and CD68, markers for lymphocytes and monocytes, respectively, were also performed on serial sections to examine the contribution of infiltrated mononuclear cells to cells positive for IL‐6 mRNA in glomeruli. Glomerular resident cells, including glomerular mesangial and epithelial cells and cells of Bowman's capsule, as well as tubular epithelial cells and infiltrated mononuclear cells expressed IL‐6 mRNA. We also compared the localization of IL‐6 mRNA and protein and showed different distribution between the gene product and protein. the expression of IL‐6 mRNA correlated with the degree of mesangial cell proliferation and tubulointerstitial changes. Our results indicate that IL‐6 is synthesized in renal tissues of IgAN and suggest that the increased IL‐6 expression may be important in the pathogenesis of IgAN.