Objective To measure the expression of CD80 and CD86 in renal tissue of lupus nephritis (LN) and explore its mechanism in the development of LN.Methods Forty-nine patients with active LN and 9 patients with minor glomerular abnormalities tissues as controls were studied.The expression of CD80, and CD86 in renal tissues was detected by immunohistochemical methods.Results CD86 was expressed extensively in glomerulus, periglomerular area, tubular epithelial cells and peritubular interstitium, while CD80 was expressed only in tubular epithelial cells and peritubular interstitium.Moreover, the percentage of CD+80 and CD+86 cells in tubular epithelial cells and peritubular interstitium showed a tendency to increase with tubulointerstitial damage.The expression of CD80 and CD86 in renal tissue correlated with the systemic lupus erythematosus (SLE) disease activity index score, the degree of proteinuria, creatinine clearance and anti- dsDNA antibody.Conclusions This study shows that increased CD80 and CD86 expression with the progression of tubulointerstitial lesion might play an important role in the development of lupus nephropathy, and the tubulointerstitial expression of CD80 and CD86 could potentially serve as a surrogate marker of SLE disease activity.The co-stimulatory molecules CDg, and CD86 might play an important role in the pathogenesis of LN.