SO031ANGIOTENSIN II TYPE 1 RECEPTOR (AT1R) EXPRESSION IN RENAL TRANSPLANT BIOPSIES AND ANTI-AT1R ANTIBODIES IN SERUM AS AN INDICATOR OF THE RISK OF TRANSPLANT LOSS

Background and Aims The manifestation of anti-angiotensin II type 1 receptor (AT1R) antibodies is considered a risk factor for transplant injury, however, the occurrence of AT1-Receptor expression in renal transplant biopsy may be an additional feature which can help to predict transplant loss. The aim of our study was to evaluate the expression of AT1R together with their antibodies and assess the risk of transplant loss in patients who had a renal transplant indication biopsy. Method AT1-Receptor immunoreactivity was analyzed in renal transplant biopsies. Additionally, we analyzed the presence of anti-AT1R antibodies in these patients using ELISA method. The result of more than 10 was assessed as positive. Immunohistochemical evaluation of AT1-Receptor expression was performed on 4 μm-thick paraffin sections mounted on silanized slides. AT1-Receptor expression was analyzed in five compartments: 1.tubular epithelium, 2.glomeruli, 3.peritubular capillaries, 4.interstitium and 5.renal blood vessels (small and intermediate arteries) based on a 3-step scale. Results We checked 156 samples of biopsies for the immunoreactivity of the AT1-Receptor. In all these patients we were able to access the presence of anti-AT1R antibodies. A group of 67 patients had positive AT1-Receptor expression (R+) and 16 patients had positive anti-AT1R antibodies (R+Ab+) results. A group of 89 patients had no expression of AT1-Receptor (R-), among which 51 had also no anti-AT1R (R-Ab-). One-year post-biopsy graft loss in the R+Ab+ patients was 37% (6/16) compared to 10% (7/69) in the R-Ab- patients (p = 0.006). Two-year and three-year graft loss was 43% vs. 17% (p=0.02) and 50% vs. 21% (p=0.02) respectively. Moreover, six patients had positive staining of AT1-Receptors in microcirculation (glomeruli and peritubular capillaries), which was associated with antibody mediated rejection. Conclusion The presence of anti-AT1R antibodies in serum together with the expression of AT1-Receptor in transplant biopsy was associated with a significantly higher graft loss. The relevance of AT1-Receptor expression analyzed together with anti-AT1R antibodies should be considered for better transplant immunological risk assessment.