Polyomavirus nephropathy in renal transplantation: a clinico‐pathological study

Polyomavirus (PV) nephropathy is a rare cause of graft dysfunction, but it may accompany acute rejection (AR), resulting in complications with respect to its diagnosis and treatment. To examine the validity of tubulitis and inflammatory phenotype in the diagnosis of concurrent AR, we reviewed the renal histology of ten biopsy samples from nine patients with PV nephropathy, and the immunohistochemistry from eight samples. Tubulitis was present in seven patients and was associated with AR in six. The degrees of tubulitis and interstitial inflammation were higher in biopsy samples with AR than in those without, but the degree of tubulitis was not related to the degree of interstitial inflammation. Virally infected cells were rare in the samples with no, or mild, tubulitis, but did not increase with the degree of interstitial inflammation. Immuno‐phenotyping of inflammatory cells did not show any T‐cell dominance in AR: T cells were dominant over B cell in three of six samples with AR and both samples without AR. Although the degrees of tubulitis and interstitial inflammation were higher in the AR subjects, the presence of tubulitis or inflammatory phenotype was not helpful in the diagnosis of concurrent AR. Further studies will be required to find a better marker for coexisting AR in patients with PV nephropathy and to establish strategies for treatment.