Background: Our previous study developed ATRQ beta-001 vaccine, which targets peptide ATR001 from angiotensin II (Ang II) receptor type 1 (AT1R). The ATRQ beta-001 vaccine could induce the production of anti-ATR001 monoclonal antibody (McAb-ATR) and inhibit atherosclerosis without feedback activation of the renin-angiotensin system (RAS). This study aims at investigating the underexploited mechanisms of McAb-ATR in ameliorating atherosclerosis. Methods: AT1R-KO HEK293T cell lines were constructed to identify the specificity of McAb-ATR and key sites of ATRQ beta-001 vaccine. Beta-arrestinl knock-out (Arrb1(-/-)) mice, Beta-arrestin2 knock-out (Arrb2(-/-)) mice, and low-density lipoprotein receptor knock-out (LDLr-/-) mice were used to detect potential signalingpathwaysaffectedbyMcAb-ATR.TheroleofMcAb-ATRinbeta-arrestinandGproteins(G(q) or G(i)(2/i3)) signal transduction events was also investigated. Results: McAb-ATR could specifically bind to the Phe(182)-His(183)-Tyr(184) site of AT1R second extracellular loop (ECL2). The anti-atherosclerotic effect of McAb-ATR disappeared in LDLr-/- mice transplanted with Arrb2(-/-) mouse bone marrow (BM) and BM-derived macrophages (BMDMs) from Arrb2(-/-) mice. Furthermore, McAb-ATR inhibited beta-arrestin2-dependent extracellular signal regulated kinase1/2 (ERK1/2) phosphorylation, and promoted beta-arrestin2-mediated nuclear factor kappa B p65 (NF kappa B p65) inactivity. Compared with conventional AT1R blockers (ARBs), McAb-ATR did not inhibit Ang II-induced uncoupling of heterotrimeric G proteins (G(q) or G(i)(2/i3)) and G(q)-dependent intracellular Ca2+ release, nor cause RAS feedback activation. Conclusions: Through regulating beta-arrestin2, McAb-ATR ameliorates atherosclerosis without affecting G(q) or G(i)(2/i3) pathways. Due to high selectivity for AT1R and biased interaction with beta-arrestin2, McAb-ATR could serve as a novel strategy for treating atherosclerosis. (C) 2021 Elsevier Inc. All rights reserved.