**2. Results**

#### *2.1. Decreased Capillary Density in Acute Rejection Biopsies*

To assess the impact of AR on the local capillary density in the kidney, we quantified the number of endothelial cells (EC) and pericytes in archival acute rejection biopsies by immunohistochemical staining of the EC for CD34 antigen and the pericytes for the CD73 marker (resp. *n* = 102 and *n* = 29). Subsequently, we compared these parameters to the available pre-transplant biopsies (resp. *n* = 78 and *n* = 66) of these patients [20]. Patient characteristics can be found in Supplementary Table S1. As shown in Figure 1, we observed a strong decrease in both the number of endothelial cells (~2.5-fold, mboxemphp < 0.0001) as well as pericytes (~6-fold, *p* < 0.0001) in AR, indicating loss of the peritubular capillary network in AR.
