CD23 is a surface marker of activated B cells as well as a low-affinity Fc receptor for IgE. In this study, we enumerated CD23-positive peripheral blood lymphocytes and evaluated their clinical significance in patients with IgA nephropathy (IgAN). Twenty-five patients with IgAN and 16 patients with non-IgA proliferative glomerulonephritis (PGN) were studied. Twenty-seven healthy adults served as controls. CD23-bearing cells were enumerated by flow cytometry, and serum IgE levels were measured by latex photometric immunoassay. Significant increases in the number of CD23-positive cells were observed in patients with IgAN (p < 0.01) and PGN (p < 0.05) compared with controls. A significant elevation of serum IgE levels was also observed in the patients with IgAN and PGN (p < 0.05). No positive correlation between the number of CD23-positive cells and serum IgE levels was observed. We also examined the induction of surface CD23 expression on peripheral lymphocytes by interleukin (IL)-2, IL-3, IL-4, IL-5, IL-6, interferon (IFN)-γ IFN-α, phytohemagglutinin, concanavalin A, pokeweed mitogen, lipopolysaccharide and phorbol myristate acetate. IL-4 was revealed to have a significantly potent effect on the induction of cell surface CD23 compared with other stimulants. It was concluded that many patients with IgAN or PGN show high serum IgE levels and/or high CD23-positive cell counts in their peripheral blood, suggesting that hyperactivation of B cells might be involved in the development of IgAN and non-IgA PGN. It appeared that IL-4 may play a significant role in the etiology of these types of glomerulonephritis.
Recent in v i m 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 .
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