Clinical relevance of immunohistochemical staining for ecto-AMPase and ecto-ATPase in chronic allograft nephropathy (CAN).

Introduction: Chronic allograft nephropathy (CAN) is a major cause of deterioration of kidney function in transplanted patients. It is thought that glomerular ischaemia may contribute to glomerular dysfunction and proteinuria in these subjects. As reduced expression of glomerular ecto-ATPase concurrent with upregulation of glomerular ecto-AMPase activity is associated with local ischaemia, we compared the expression of these glomerular ecto-enzymes in kidney biopsies from subjects with CAN or with acute rejection vs normal human kidney tissue.

Methods: Kidney biopsies in comparison with normal kidney tissue samples (n = 10) were studied from subjects with CAN (n = 6), acute interstitial rejection (n = 13), acute vascular rejection (n = 3), or subjects whose biopsies were histologically difficult to classify (n = 8). Cryostat sections (4 micro m) were stained for ecto-ATPase using standard procedures. For the demonstration of ecto-AMPase activity, conventional enzyme histochemistry was used. Reaction product of individual sections was quantified using computerized image analysis.

Results: The results clearly show decreased expression of glomerular ecto-ATPase in combination with increased glomerular ecto-AMPase in all biopsies from subjects with CAN vs normal kidney tissue (P < 0.001). Although to a lesser extent, this staining pattern was also observed in patients with vascular rejection as well as in subjects whose biopsies were histologically difficult to classify (P < 0.01), while biopsies from subjects with interstitial rejection and normal control tissue stained negative for glomerular ecto-AMPase.

Conclusion: In CAN diminished glomerular ecto-ATPase expression occurs in association with significantly enhanced activity of glomerular ecto-AMPase. This is a strong indication for ischaemic injury of the glomerular microvasculature. As positive staining for ecto-AMPase in acute rejection episodes may be an important sign for long-term prognosis, we feel that screening of biopsies from individual subjects for glomerular ecto-AMPase activity should be considered.