Evaluation of Microvascular Inflammation in ABO-Incompatible Kidney Transplantation

Background. In ABO-incompatible kidney transplantation, the diagnostic criteria for antibody-mediated rejection remain controversial because C4d deposition is commonly observed. Thus, we investigated microvascular inflammation (MVI score = 2) within 1 year as a predictor of graft outcome. Methods. A total of 148 recipients without preformed or de novo donor-specific anti-HLA antibody were stratified based on MVI score less than 2 (n = 117) and MVI score of 2 or greater (n = 31). Results. We found that 5-year graft survival was significantly lower (P = 0.0129) in patients with MVI (89.8%) than in patients without MVI (97.0%). Graft function, as characterized by serum estimated glomerular filtration rate, was also significantly worse for patients with MVI than it was for patients without MVI, between 3 months and 10 years after transplantation (P = 0.048). Multivariate analysis indicated that HLA class II mismatch (P = 0.0085) was an independent marker of MVI. Conclusions. Microvascular inflammation score of 2 or greater is significantly associated with poor graft outcome after ABO-incompatible kidney transplantation. We suggest that MVI score of 2 or greater in ABOi transplantation be used as a basis to diagnose antibody-mediated rejection.