Purpose: The diagnosis of acute antibody-mediated rejection (ABMR) is according to following all three evidences: 1) histologic evidence , 2) evidence of interaction with vascular endothelium (C4d staining in peritubular capillaries), and 3) serologic evidence of donor- specific antibodies. In the ABO-incompatible kidney transplantation (ABOI KTx), the diagnosis of acute AMR does not necessarily satisfy with this criterion because C4d deposition in the pritubular capillaries and anti-blood group antibodies are commonly observed after ABOI KTx. Therefore, the histologic evidence of acute tissue injury is the most important for diagnosis of acute AMR. The histologic evidence includes the following four features: microvascular inflammation (MVI), intimal arteritis, thrombotic microangiopathy (TMA), and acuter tubular injury. The purpose of this study was to assess which histologic evidence was associated with subsequent renal dysfunction in ABOI KTx.

Methods: A total of 154 ABOI incompatible kidney transplants were performed at Tokyo Womens Medical University from 2005 to 2013 .Among them, 122 patients underwent renal allograft biopsies within 3 month after ABOI KTx. Twenty-two patients, who had pre-operative donor specific anti-HLA antibodies were excluded . Finally, 100 recipients were included in this study. The study cohort was divided into three groups according to the estimated glomerular filtration rate (eGFR ) at one year after Tx; Group 1: eGFR >60( n=19), Group 2: 45< eGFR <59 (n=40), Group 3: eGFR<45 (n=41).

Results: Three grafts in the Group 3 were lost until 2014. MVI (g+ptc) ≥1 in the early biopsies was not associated with graft dysfunction (p=0.12, Group 1: 11%, Group 2: 18%, Group 3: 32%). Intimal arteritis developed in 9 recipients during the first three-month and was observed only in the Group 3 (p=0.0008). Only three recipients in the Group 3 developed TMA, but it was not significant. Acute tubular injury and other pathological features such as C4d deposition, tubulitis, and interstitial inflammation in the early biopsies were not associated with subsequent renal impairment.

Conclusions: Among the histologic features of acute AMR, only intimal arteritis is significantly associated with renal dysfunction at one year posttransplant.

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