AIM:To investigate the role of hepatitis B virus(HBV)inthe pathogenesis of IgA nephropathy(IgAN).METHODS:HBV antigens(HBAg,or HBsAg,HBcAg,andHBeAg)in renal tissues with IgAN were detected byimmunohistochemical technique.The distribution andlocalization of HBV DNA were observed by using in situhybridization.Southern blot analysis was performed to revealthe state of renal HBV DNA.RESULTS:Among 100 patients with IgAN,HBs antigenemiawas detected in 18 patients(18.00 %).HBAg in renal tissueswas detected in 31 patients(31.00 %),the positive rate ofHBAg,HBsAg and HBcAg was 64.52 %(20/31),32.26 %(10/31),32.26 %(10/31),respectively in glomeruli.HBcAgwas also found in tubular epithelia and interstitia,whichwas 45.16 %(14/31)and 6.45 %(2/31),respectively.Fiveout of six cases with positive HBV DNA by in situ hybridizationwere proved to be HBV DNA positive by Southern blotanalysis,and all were of the integrated form.Eight specimenswere demonstrated to be HBV DNA positive by in situhybridization,which was localized in the nuclei of tubularepithelial cells and glomerular mesangial cells as well as ininfiltrated interstitial lymphocytes.CONCLUSION:There is a relationship between HBV infectionand IgAN.In addition to the humoral immune damagemediated by HBAg-HBAb immune complex,the cellularmechanism mediated by HBV originating from renal cells insitu may be also involved in the pathogenesis of IgAN. AIM: To investigate the role of hepatitis B virus (HBV) inthe pathogenesis of IgA nephropathy (IgAN). METHODS: HBV antigens (HBAg, or HBsAg, HBcAg, andHBeAg) in renal tissues with IgAN were detected by immunohistochemical technique. The distribution and localization of HBV DNA were observed by using in situ hybridization. Southern blot analysis was performed to reveal the state of renal HBV DNA. RESULTS: Among 100 patients with IgAN, HBs antigenemia was detected in 18 patients (18.00%). HBAg in renal tissues was detected in 31 patients ( 31.00%), the positive rate of HBBA, HBsAg and HBcAg was 64.52% (20/31), 32.26% (10/31), 32.26% (10/31) respectively in glomeruli. HBcAgwas also found in tubular epithelia and interstitia, whichwas 45.16% (14/31) and 6.45% (2/31), respectively. Five cases of positive HBV DNA by in situ hybridization were proved to be HBV DNA positive by Southern blot analysis, and all were of the integrated form. Light specimenswere demonstrated to be HBV DNA positive by in situhybridization, whi ch was localized in the nuclei of tubularepithelial cells and glomerular mesangial cells as well as ininfiltrated interstitial lymphocytes. CONCLUSION: There is a relationship between HBV infection and IgAN. addition to the humoral immune damage by HBAg-HBAb immune complex, the cellular mechanism of mediated by HBV originating from renal cells insitu may be also involved in the pathogenesis of IgAN.