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Aripiprazole (ARP) is a partial agonist of dopamine D2 receptors that is commonly prescribed to treat schizophrenia and bipolar disorder. The anti-inflammatory effect of ARP was recently documented in a few studies, but its molecular mechanisms have not been fully elucidated. In this study, peptidoglycan (PGN)-treated macrophages (RAW264.7 cells), reporter gene assay, an overexpression strategy, immunoprecipitation, and immunoblotting analysis were employed to clarify the anti-inflammatory mechanism of ARP. ARP was found to dose-dependently inhibit production of nitric oxide (NO) and prostaglandin E2 (PGE2) without exhibiting cytotoxicity. In agreement with this result, ARP was found to suppress the mRNA expression levels of inflammatory genes such as cyclooxygenase-2 (COX-2), inducible NO synthase (iNOS), and tumor necrosis factor (TNF)-α. Luciferase assay and immunoblotting analysis with nuclear fractions showed that activator protein-1 (AP-1) and nuclear factor (NF)-κB are targeted by ARP. Similar to these data, c-Jun N-terminal kinase (JNK), mitogen-activated protein kinase kinase 4 (MKK4), MKK7, and transforming growth factor beta-activated kinase 1 (TAK1) for AP-1 activation, and inhibitor of κBα (IκBα), IκBαkinase α/β (IKKα/β), AKT, phosphatidylinositide 3-kinases (PI3K), spleen tyrosine kinase (Syk), and Src for NF-κB activation were revealed to be inhibited by ARP treatment. These results suggest that ARP can suppress inflammatory responses triggered by Gram positive bacteria through suppression of both AP-1 and NF-κB pathways.