A Preliminary Study Into the Significance of Intrarenal Reflux in BK Virus Nephropathy After Kidney Transplantation

BACKGROUND The BK virus typically colonizes the lower urinary tract and is the causative agent in BK virus nephropathy (BKVN), which can progress to allograft dysfunction and graft loss. Urinary reflux in kidney allografts is induced by vesicoureteral reflux or disturbances in intrarenal reflux (IRR), believed to be associated with BKVN. This study was designed to elucidate the relationship between BKVN and IRR. METHODS We examined 30 renal transplant recipients histologically diagnosed with BKVN using anti-Simian virus 40 immunohistochemistry and 60 clinically matched control recipients. The BKVN patients were divided into stable (n = 12) and progressive (n = 18) groups according to allograft kidney function 1 year after diagnosis. Histological rejection scores according to the pathological classification of rejection in renal allografts (Banff classification), histological BKVN stages, and histological polyomavirus load levels (pvl) proposed by the Banff working group were evaluated. The IRR was quantified by histological reflux scores defined with retention and reflux of immunostained Tamm-Horsfall protein in renal tubules and glomeruli. RESULTS Higher reflux scores were observed in the BKVN group compared with that in the control group. No differences in clinical parameters were observed between the BKVN and control groups. Reflux scores and pvl were significantly higher in the progressive group than in the stable BKVN group with no significant difference in BK stage observed between groups. Reflux scores were found to be significantly correlated with pvl. CONCLUSIONS Our preliminary study suggested that IRR might be a predisposing and prognostic factor in BKVN.