Tubuloreticular inclusions in peritubular capillaries of renal allografts

Background Tubuloreticular inclusions (TRIs) are anastomosing networks of microtubules that are frequently found in autoimmune diseases and viral infections. In renal allografts, TRIs have been reported in glomerular endothelial cells in association with viral infections and donor specific antibodies (DSAs), but their presence in peritubular capillaries has not been explored. Methods We collected seven cases with TRIs out of 148 consecutive renal allograft biopsies taken from Dec. 2015 to Dec. 2016. Results TRIs were present in peritubular capillaries in seven cases and were concomitantly present in glomerular endothelial cells in two cases. The diagnoses included polyomavirus nephropathy (n = 2), acute T cell-mediated rejection (ACR) (n = 1), combined ACR and antibody-mediated rejection (AMR) (n = 1), suspicious for ACR (n = 1), chronic active AMR (n = 1), and moderate tubular atrophy and interstitial fibrosis (n = 1). Six patients had recent or current viral infections (BK polyomavirus, hepatitis B virus, herpes simplex virus, and cytomegalovirus in two, two, one, and one case, respectively). DSA was positive in one case. Five cases had moderate to severe interstitial inflammation and four cases had peritubular capillaritis. Conclusion TRIs are not rare in peritubular capillaries. They are associated with various viral infections and their appearance seems to be related to peritubular capillary injury.