The Summarized Assessment of Endothelin A Receptor Expression in Renal Transplant Compartments Associated with Antibody-Mediated Rejection

Abstract

The occurrence of anti-endothelin A receptor antibodies may be useful in diagnosis of transplant damage. We noticed that the presence of the endothelin A receptor (ETA receptor) in biopsy compartments is yet to be defined. We decided therefore to analysed the presence and relevance of the ETA receptor in biopsy to define the cause. Our study aims to evaluate the expression of ETA receptors in renal recipients after a biopsy due to the worsening of transplant function.

Methods: The expression of ETA receptors was analyzed in renal transplant biopsies using the immunohistochemical method. The evaluation of ETA receptors was performed on paraffin sections. ETA receptor expression was analyzed in four compartments of renal transplant biopsies: glomeruli; vessels; tubular epithelium; and interstitium. The assessment was presented using a three-step scale (0: lack of expression; 1: mild to moderate immunoreactivity; 2: high expression). The results of each compartment from a single biopsy were summarized and assessed in the context of antibody-mediated rejection (AMR).

Results: We analyzed 156 patients who had a renal allograft biopsy after renal transplantation. For each patient, we created a summarized ETA receptor expression score. The summarized ETA receptor expression score analysis showed statistically significant differences in patients with and without AMR. In addition, we noticed that patients with AMR had a significantly higher mean summarized expression of ETA receptor score of 3.28 ± 1.56 compared to patients who had a biopsy for other reasons with a mean summarized ETA receptor expression score of 1.47 ± 1.35 (p < 0.000001). ROC analysis of the ETA receptor expression score for detecting AMR status showed that the most appropriate cut-off for the test of the chosen binary classifier is between 2 and 3 of the summarized ETA receptor expression score.

Conclusions: The expression of endothelin A receptors in renal transplant compartments may be associated with antibody-mediated rejection. The positive ETA receptor staining might be a vital feature in the diagnosis of damage in AMR. The summarized ETA receptor expression score seems to be an exciting diagnostic tool in transplant injury assessment.

Keywords: allograft injury; antibody-mediated rejection; endothelin A receptors; non-HLA antibodies.

Figure 1

(A) High ETAR expression in tubular epithelium, glomerulus, and renal interstitium (chronic inflammatory cells and stromal fibroblasts) (200×, hematoxylin). (B) ETAR expression predominantly located in tubular epithelium (100×, hematoxylin). (C) ETAR immunoreactivity in endothelial cells of artery with focal expression in tubular epithelium (600×, hematoxylin). (D) High ETAR expression in tubular epithelium with immunoreactivity in endothelial cells (400×, hematoxylin).

Figure 2

The summarized ETA receptor expression score according to AMR.

Figure 3

ROC analysis of ETA receptor expression score for detecting AMR status. The most appropriate cut-off for the test of the chosen binary classifier is between 2 and 3 of the summarized ETA receptor expression score at the highest true positive rate, together with the lowest false positive rate, which amount to 72% and 80%, respectively (see Figure 2). Based on the calculated AUC, it can be established that the accuracy of the classification of positive AMR using the level of summarized ETA receptor expression score reached 80% (since the lower limit of the AUC 95% confidence interval is greater than 50%, this result should be considered statistically significant, i.e., p > 0.05). Then, it allows to state that 80% of patients would be correctly diagnosed taking only the level of the summarized ETA receptor expression score into account.