Pathological characteristics of polyomavirus nephropathy complicated with acute rejection after renal transplantation

Objective To summarize the pathological characteristics of polyomavirus-associated nephropathy combined with acute rejection after renal transplantation. Methods The pathological data of 172 patients diagnosed as having polyomavirus nephropathy in our hospital from 2007 to 2018 were reviewed. Results One hundred and seventy-two patients were diagnosed as having polyomavirus nephropathy without acute rejection for the first time. In 75 (43.6%, 75/172) patients who received repeat biopsy, 10 (5.8%, 10/172) patients developed acute rejection with an average interval of 4.8±3.3 months. Common pathological features included: renal tubular epithelial cells virus inclusions reduced or even disappeared or only hyperchromatic nuclei revealed, SV40-T antigen (70%, 7/10) staining negative or decreased significantly (30%, 3/10), and varying degrees of interstitial inflammation, tubulitis, interstitial fibrosis and tubular atrophy. Four patients developed acute T cell-mediated rejection (Banff IIA), revealing aggravating tubulitis and interstitial inflammation in the area of negative SV40-T antigen (70%, 7/10) staining, as well as mild endarteritis. Three patients developed acute antibody-mediated rejection, revealing glomerulitis and peritubular capillaritis and positive panel reactive antibody. Only 1 patient revealed C4d deposition of peritubular capillaries. Two patients developed mixed rejection, revealing tubulitis, interstitial inflammation, glomerulitis, peritubular capillaritis, mild endarteritis and C4d deposition of peritubular capillaries. One patient developed suspicious T cell-mediated rejection (Banff IB), revealing aggravating tubulitis and interstitial inflammation in the non-fibrotic areas but without intimal arteritis. Besides, the positive SV40-T antigen (70%, 7/10) staining area was reduced significantly. Conclusion The pathological characteristics of polyomavirus nephropathy combined with acute rejection include endarteritis, glomerulitis, peritubular capillaritis and C4d deposition of peritubular capillaries. It is difficult to distinguish polyomavirus nephropathy from Banff I T cell-mediated rejection. Clinical information and repeat biopsy results are helpful for differential diagnosis. Key words: Kidney transplantation; Acute rejection; Pathology