Mast cell quantitation in renal transplant biopsy specimens as a potential marker for the cumulative burden of tissue injury

Although mast cells (MC) play an ambiguous role in acute rejection, they have been implicated in chronic fibrotic processes overall and also in the kidney. Their morphological assessment in the context of comprehensive renal allograft pathology has not been sufficiently addressed, however. Using the CD117 immunostain in 461 consecutive kidney allograft biopsy specimens we counted the number of MC in the most inflamed biopsy area. The number of MC was correlated with the presence of the Banff defined features of T-cell-mediated and antibody-mediated rejection. No correlation was found between the number of MC and the presence or degree of T-cell-mediated rejection or with most parameters defining acute or chronic antibody-mediated rejection. Significant correlation was found, however, with the degree of interstitial fibrosis (IF; P =.000), and time post- transplantation (P =.000). Peritubular C4d staining correlated negatively with the number of MC (P =.000). Correlation of MC infiltration and peritubular capillary multilamellation (P =.000) indicated an association between general interstitial and microvascular chronic pathology. We conclude that MC represent a somewhat unique cellular component that correlates poorly with parameters of active T-cell or antibody-mediated allograft rejection. In contrast, because MC correlate strongly with IF and time post-transplantation, they could potentially be valuable as a surrogate marker for the cumulative burden of tissue injury.