Peritubular Capillary Morphometry in Renal Allograft Biopsies with Active Antibody-mediated Rejection

Abstract

Background: Microvascular inflammation characterized by peritubular capillaritis and/or glomerulitis is an evidence of tissue injury and antibody interaction in antibody-mediated rejection (ABMR) of renal allografts. According to the Banff classification, endothelial cell (EC) swelling and leucocyte infiltration characterize glomerulitis. Objective: We evaluated the significance of peritubular capillary (PTC) density, dilatation and EC swelling in early renal allograft biopsies and correlated it with clinicopathological features. Methods: Consecutive, early (<one year) renal allograft indication biopsies over a period of one year were included. PTC density was determined by analysing the average CD31-positive PTCs per tubule and per ten 20x microscopic field by image analysis. PTC capillary dilatation and EC swelling  was recorded Results: 27 of the 95 graft biopsies from 75 recipients were diagnosed as ABMR/mixed rejection. The mean PTCs per ten 20x field and per tubule in graft biopsies with ABMR were 144±5 and 2.7±0.38 respectively. The mean PTCs/ten 20x fields and per tubule did not show significant correlation with age, C4d positivity and presence of donor specific antibodies (DSA). PTC dilatation and endothelial cell swelling correlated significantly with peritubular capillaritis and DSA. Conclusion: Our results show that PTC dilatation and PTC-endothelial cell swelling  are associated with peritubular capillaritis and are additional morphological features of active ABMR, especially useful in the diagnosis of C4d-negative ABMR.