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Angiotensin type 1 receptor (AT1R) mediates most physiologic and pathophysiologic actions of its endogenous ligand, angiotensin II, with overactivity leading to vascular remodeling and hypertension. Antibodies to AT1R are implicated in several vascular pathologies. The aim of our study was to determine the impact of antibody to AT1R on clinical outcomes including antibody mediated rejection (AMR), with or without C4d deposition, in patients whose sera contained no donor human leukocyte antigen (HLA)-specific antibody (HLA-DSA).Pretransplant sera from 97 recipients and sera obtained at the time of acute rejection (AR) were tested by Luminex-based single-antigen bead assays to determine HLA-DSA and antibodies to major histocompatibility class I chain-related gene A (MICA). The presence of antibody to AT1R was determined by a cell-based ELISA method using a cutoff of 17 units to distinguish high from low binding.Sera from 63 recipients were determined to have no HLA-DSA and no donor-specific MICA antibodies pretransplant and at the time of AR, and 16 of these recipients were diagnosed with AR including 7 with AMR and 9 with cellular AR (cell-mediated rejection). High-binding AT1R antibodies were identified for six of seven in the AMR+ group and zero of nine in the cell-mediated rejection+ group (P=0.0009).A strong association was observed between the presence of high binding to AT1R and AMR in recipients whose sera contained no antibody to donor HLA or MICA. Assessing the AT1R antibody status along with the HLA-DSA provides additional information to determine the immunologic risk for recipients.