Myeloperoxidase Staining Identifies Endothelial Injury of Peritubular Capillaries and Glomeruli in Renal Antibody-Mediated Rejection.

Objective: It remains unclear if C4d staining is related to any peritubular and glomerular injury during antibody mediated rejection (ABMR). The goal of this study was to determine if myeloperoxidase (MPO) staining can highlight endothelial injury in peritubular capillaries (PTC) and glomeruli.

Methods: The study included 12 native negative controls, 19 transplant biopsies with borderline changes (BC) as transplant controls, and one group of renal transplant biopsies with ABMR as the study group (acute/chronic, n=22). All three groups were stained for MPO immunohistochemically, and the MPO expressions in the endothelium of PTC and glomeruli were evaluated and correlated with serum creatinine (SCr). In addition, the ultrastructural layers of the PTC (an index for chronic allograft rejection) were correlated with MPO indices in PTC.

Results: The negative control group and the transplant controls showed no MPO expression in the endothelium of glomeruli and PTC. However, in the biopsies with ABMR, there were MPO-positive stains in the endothelial cells of glomeruli (15/21 cases, 71.4 %) and PTC (16/22 cases, 72.7 %). There were significant correlations between the peritubular MPO staining versus SCr (r=0.355 and =0.0106) and glomerular MPO staining versus SCr (r=0.365 and =0.0092). Furthermore, the layers of PTC by electron microscopy were significantly correlated with MPO scores in PTC (r=0.696, =0.0001).

Conclusion: Our data suggest that the MPO-positive endothelial injuries are most likely the cause leading to renal graft dysfunction following ABMR.