Aryl hydrocarbon receptor (AhR) restrains the maintenance and acquisition of the anti-inflammatory identity of monocyte-derived macrophages.

The Aryl hydrocarbon receptor (AhR) is an essential environmental sensor bridging metabolic cues with immune regulation, yet its precise role in defining human monocyte-derived macrophage identity remains unclear. Here, we demonstrate that AhR functions as a critical transcriptional rheostat that selectively restrains the anti-inflammatory and pro-fibrotic identity of M-CSF-dependent monocyte-derived macrophages (M-Mac). Integrated ChIP-Seq and transcriptomic profiling revealed that AhR activity is enriched in M-Mac in a MAFB-dependent manner, directly occupying regulatory regions of core M-Mac identity genes, including CD163, LGMN, and IL10. Unexpectedly, siRNA-mediated knockdown and CRISPR/Cas9 ablation demonstrated that AhR primarily functions as a repressor; its deficiency accelerated and exacerbated the acquisition of a "resident-like" (LYVE1+/FOLR2+) and pro-fibrotic phenotype. Functionally, AhR restricted the M-Mac anti-inflammatory response to TLR7 ligation, and limited an overly tolerogenic profile during M-Mac-driven T-cell responses. Pharmacological modulation using the endogenous ligand FICZ and the antagonist SR1 confirmed that AhR activity limits the magnitude of the MAFB-driven program and the autocrine IL-10 signaling axis. Collectively, these findings establish AhR as a fundamental checkpoint that prevents macrophages from acquiring an excessive anti-inflammatory state, thereby ensuring balanced responses essential for tissue homeostasis and immune surveillance.