CCL1 (C-C motif chemokine ligand 1) is an anti-inflammatory chemokine that primarily functions in immune regulation and tissue homeostasis. CCL1 is produced by alternatively activated M2 macrophages as part of the anti-inflammatory cytokine milieu, alongside IL-10 and TGF-β 1. The chemokine specifically binds to CCR8 receptors and plays a critical role in recruiting regulatory T cells (Tregs) to specific tissue sites 2. In reproductive immunology, CCL1 produced by decidual natural killer cells attracts CCR8+ Tregs to the maternal-fetal interface, where these cells maintain immune tolerance during pregnancy 3. CCL1 also facilitates bone repair by recruiting CCR8+ Tregs that secrete progranulin to support skeletal stem cell function 4. However, CCL1 has pathological roles in cancer, where it contributes to immune suppression by recruiting CCR8+ Tregs to the tumor microenvironment, thereby inhibiting anti-tumor immune responses 25. In hepatocellular carcinoma, tumor-derived N1-acetylspermidine induces CCL1+ macrophage polarization, creating an immunosuppressive environment that reduces the efficacy of immune checkpoint blockade therapy 5. This dual role demonstrates CCL1's context-dependent function in both protective immunity and pathological immune suppression.