NOVEL IMMUNOHISTOCHEMICAL MARKERS OF HUMAN RENAL ALLOGRAFT DYSFUNCTION—ANTITHROMBIN III, THY-1, UROKINASE, AND ALPHA–SMOOTH MUSCLE ACTIN

Expression of urokinase plasminogen activator and its receptor during acute renal allograft rejection

BACKGROUND

In inflammation, urokinase plasminogen activator (uPA) and its receptor (uPAR) play an important role in fibrinolysis and in activation and chemotaxis of neutrophils and lymphocytes. Moreover, the uPA/uPAR system is involved in processes that affect turnover of the extracellular matrix (ECM). The aim of this study was to determine the local and systemic release of uPAR, and the expression of uPA and uPAR in renal tissues during acute renal allograft rejection.

METHODS

Blood, urine, and tissue samples were collected from 33 patients diagnosed with acute allograft rejection and from 14 transplant patients without rejection. From 10 healthy volunteers, blood and urine were collected as a control. In urine and blood samples, the levels of uPAR were determined by enzyme-linked immunosorbent assay (ELISA). Immunostaining and in situ hybridization for uPA and uPAR were performed on renal biopsies.

RESULTS

uPAR was detectable at low levels in serum and urine of healthy volunteers and was increased in nonrejecting allograft recipients. Serum and urine levels of uPAR were higher in transplant recipients with rejection compared to nonrejectors. The urine and serum levels of uPAR correlated with the renal function. Immunostaining and in situ hybridization showed an up-regulation of both uPA and uPAR in rejection biopsies. Nonrejected grafts displayed no expression of uPA and uPAR by immunostaining, or of uPAR by in situ hybridization. uPA was detected in a limited number of tubular epithelial cells by in situ hybridization. During rejection, lymphocytes as well as tubular epithelial cells showed uPA and uPAR expression. In the vascular types of rejection, strong expression of uPA was also seen in the entire vessel wall, while uPAR was expressed by the endothelium.

CONCLUSION

This study shows that (1) uPA and uPAR are up-regulated during acute renal allograft rejection; (2) uPAR levels in urine and serum correlate with serum creatinine levels, and (3) uPA and uPAR are produced by inflammatory cells, tubular epithelium, and vascular endothelium during acute renal allograft rejection.

Localization and characterization of antithrombin in human kidneys

Antithrombin is a serine protease inhibitor that is critical in maintaining a thromboresistant vasculature. The association between low serum antithrombin concentration and renal disease suggests that the kidney plays a role in the conservation of plasma antithrombin. We used immunohistochemical techniques to determine the spatial distribution, heparin binding characteristics, and intracellular and intercellular localization of antithrombin in biopsy specimens (n = 53) of human donor kidneys obtained at the time of transplantation. In the renal cortex, double antibody techniques demonstrated the presence of intracellular antithrombin in proximal tubule epithelial cells. The reactivity was granular and was co-localized with vesicle-like structures. Distal and collecting tubules did not demonstrate intraepithelial antithrombin reactivity. No tubule structures in the medullary region demonstrated intracellular antithrombin, but all these structures showed intense basement membrane antithrombin reactivity. Double antibody techniques also demonstrated that the heparin binding domain of intraepithelial antithrombin was occupied. Semiquantitative scores for intraepithelial antithrombin were significantly decreased in renal biopsy specimens obtained 30 min after anastomosis compared with biopsies from the same organ obtained before anastomosis. These findings suggest that antithrombin, probably in association with heparin or heparan sulfate, is internalized by renal proximal epithelial cells. Although the ultimate fate of intraepithelial antithrombin is not known, this may represent a mechanism by which the kidney helps to maintain plasma antithrombin concentrations.

alpha-smooth muscle actin and collagen deposition in dysfunctional renal transplants

In normal kidneys, alpha-smooth muscle actin and collagen type III expression is restricted to vascular smooth muscle cells and perivascular fibrous tissues, respectively, but in pathological conditions their expression or deposition is more extensive. Using immunohistochemistry, we examined the expression of alpha-smooth muscle actin and type III collagen in 31 human renal transplant biopsy specimens obtained from patients with graft dysfunction. We found that dysfunctional renal transplants have increased alpha-smooth muscle actin and collagen III expression in the glomerulus and interstitium, but only glomerular alpha-smooth muscle actin expression correlates with graft function and prognosis.

Sites of urokinase-type plasminogen activator expression and distribution of its receptor in the normal human kidney

The urokinase-type plasminogen activator (uPA) is secreted into the urine at high concentrations and both the uPA protein and mRNA are present in human renal tissue. Normal kidney tissue also expresses the receptor for uPA. Neither the precise sites of uPA mRNA expression, nor the distribution of the uPA-receptor antigen, have been elucidated in the human kidney. In the present study, the sites of uPA mRNA expression were identified by in situ hybridization, and the cellular localization of both uPA and uPA-receptor was determined by immunohistochemical analysis. High-level uPA mRNA expression was restricted to epithelial cells of the convoluted proximal tubules and the thick ascending limb of Henle's loop (the straight part of the distal tubule). However, uPA immunoreactivity was not confined to sites of uPA mRNA expression, but was present in all segments of the tubular epithelium. Tubular epithelial cells also exhibited a consistent immunoreactivity with uPA-receptor antibody, indicative of a co-localization of the uPA antigen and its receptor in the uriniferous epithelium. We propose that the uPA antigen expression in nephron segments lacking demonstrable endogenous uPA synthesis may be the result of a uPA-receptor-mediated uptake of uPA.

Tissue plasminogen activator, plasminogen activator inhibitor-1, and fibrin as indexes of clinical course in cardiac allograft recipients. An immunocytochemical study

BACKGROUND

Tissue-type plasminogen activator (TPA) is the principal activator of plasminogen. Since hemostasis in the microcirculation of allografts is a well-recognized complication of transplantation, we asked (1) whether the distribution and amount of cellular TPA in biopsies of transplanted human hearts are associated with fibrin deposits in and around the microcirculation, (2) whether such changes involve the physiological inhibitors of TPA and plasmin, and (3) whether the presence of these activators and inhibitors of fibrinolysis in tissue is correlated with clinical outcome.

METHODS AND RESULTS

We immunocytochemically quantified the presence of fibrin, plasmin, TPA, and the TPA inhibitor PAI-1 in 938 biopsies from 68 consecutive cardiac allografts over a 54-month period. The localization, distribution, and quantification of TPA in arteriolar smooth muscle cells revealed that 35 of the 68 allografts maintained vascular TPA reactivity consistent with time-zero biopsies of autologous donor hearts: this was designated as the normal TPA group. In contrast, 33 of the 68 allografts significantly lost vascular TPA reactivity compared with time-zero biopsies of autologous donor hearts: this was designated as the depleted TPA group. Analysis of sequential biopsies from both groups during 54 months revealed that the mean cumulative quantitative TPA value for the normal TPA group was 1.0 +/- 0.01, whereas the depleted TPA group value was 1.9 +/- 0.02 (P = .0001), and the mean cumulative quantitative fibrin value for the normal TPA group was 1.0 +/- 0.01, whereas the depleted TPA group value was 1.5 +/- 0.05 (P = .0001). Biopsies of allografts in the depleted TPA group contained endothelial reactivity for TPA-PAI-1 complexes, whereas biopsies from the normal TPA group did not. Plasmin-associated molecules were rarely identified in biopsies of the normal TPA group but were present in the depleted TPA group, and the fibrin-to-plasmin ratio in the normal TPA group always was less than the fibrin-to-plasmin ratio in biopsies from the depleted TPA group. Analysis of demographic and risk factors revealed no significant differences between patients in the normal and depleted TPA groups, but none of the 35 patients in the normal TPA group died or were retransplanted, and 13 of the 33 patients in the depleted TPA group died or required retransplantation (P = .0001).

CONCLUSIONS

Time-zero hearts (n = 68) and 34 of 38 stable allografts contained immunocytochemically detectable TPA only in vascular smooth muscle cells. Twenty-nine of 30 patients with normal TPA in their time-zero biopsies who subsequently developed a poor clinical outcome were found to have depleted TPA in biopsies evaluated during their first postoperative month and remained depleted throughout the study. Of 33 patients with depleted TPA, 39% died or required retransplantation. Depleted arteriolar TPA associated significantly with vascular and interstitial deposits of fibrin, plasmin, and endothelial TPA-PAI-1 complexes. These findings indicate that hemostatic and fibrinolytic pathways are activated in falling allografts, and they reveal evidence of depleted TPA before clinical or histopathological signs of failure. Patients with such allografts were found to be at high risk of death independently of other widely used clinical/laboratory parameters of prediction.