Immunohistochemical features of BK virus nephropathy in renal transplant recipients.

BK virus nephropathy (BKVN) is one of the factors that reduces renal graft function after transplantation. However, BKVN and rejection present similar pathological findings, as both are accompanied by cellular infiltration to the interstitium and tubulitis, thus they are difficult to distinguish for diagnosis and medical treatment. In the present study, we examined immunohistochemical pathological features of BKVN in four cases treated in our hospital from 2007 to 2010. Common immunohistological finding is that tubulitis in these cases was primarily EMA and 34βE12-positive and existed predominantly from the collecting duct to the distal convoluted tubule. The majority of infected cells existed in EMA and 34βE12-positive tubules, which were also located mainly from the collecting duct to the distal tubule. In addition, a large number of SV40-positive infected cells were similarly seen. Dylon staining clearly revealed eosinophils. We concluded that the main pathological features of BKVN are the presence of tubulitis and infected cells predominantly from the collecting duct to distal tubule and the appearance of eosinophils.