Mechanisms of Chronic Renal Allograft Rejection. II. Progressive Allograft Glomerulopathy in Miniature Swine

We have reported that in thymectomized miniature swine treated with a 12-day course of cyclosporin A that major histocompatibility complex class I-mismatched renal allografts either progress to chronic rejection (progression group; n = 4) or tolerance after acute rejection (recovery group; n = 4). Two types of glomerulopathies, termed acute and chronic allograft glomerulopathy, occur in allografts in this model. Morphological and immunohistochemical studies were performed on serial renal biopsies from both groups to examine the pathogenic mechanisms of acute and chronic allograft glomerulopathy. In acute rejection, acute allograft glomerulopathy developed in both groups by Day 18, with antibody deposition and T cell and macrophage infiltration. In situ DNA nick end-labeling (TUNEL)+ injured glomerular endothelial cells appeared from the early phase, followed by destruction of the glomerular capillary network with segmental mesangiolysis. Thereafter, in the progression group, acute allograft glomerulopathy progressed to chronic allograft glomerulopathy during the development of chronic rejection. This process was associated with persistent T cell and macrophage infiltration, antibody deposition, and TUNEL+ glomerular endothelial injury in the glomeruli. Impaired capillary repair, mesangial cell proliferation, and activation were still noted at Day 100, together with accumulation of mesangial matrix and duplication of glomerular basement membrane. In contrast, in the recovery group, acute allograft glomerulopathy recovered by Day 100, associated with the resolution of cellular infiltration and reduction of antibody deposition. We conclude that the acute and persistent cell- and antibody-mediated rejection against glomerular endothelial cells is the key pathogenic determinant of acute allograft glomerulopathy and progression toward chronic allograft glomerulopathy. Impaired capillary repair and phenotypic change of endothelial and mesangial cells also contribute to the development of chronic allograft glomerulopathy. With the development of tolerance, substantial recovery of acute allograft glomerulopathy can occur after the resolution of glomerular inflammation.