ARG1 (arginase 1) catalyzes hydrolysis of L-arginine into L-ornithine and urea, functioning primarily in nitrogen detoxification within the urea cycle 1. Beyond its hepatic metabolic role, ARG1 plays critical immunoregulatory functions by competing with nitric oxide synthase for arginine substrate, thereby controlling arginine bioavailability and modulating immune responses 2. In myeloid cells, ARG1 expression defines alternatively activated macrophages and suppresses T cell proliferation through arginine depletion 23. In pancreatic cancer, ARG1 drives immune suppression by depleting arginine and inhibiting CD8+ T cell activation; genetic deletion or pharmacological inhibition with CB-1158 increases T cell infiltration and sensitizes tumors to checkpoint blockade 3. In stroke, STAT6-mediated ARG1 expression promotes microglia/macrophage-mediated efferocytosis of dying neurons, accelerating inflammation resolution and improving functional outcomes 4. Conversely, in ischemia/hypoxia-induced vascular dysfunction, elevated ARG1 drives pathological mitochondrial cristae remodeling and vascular smooth muscle cell PANoptosis via the cGAS-STING pathway 5. In pancreatic ductal adenocarcinoma, NET-associated human ARG1 is cleaved by cathepsin S into catalytically enhanced forms; anti-ARG1 monoclonal antibodies restore CD8+ T cell function and enhance immunotherapy efficacy 6. ARG1 deficiency causes hyperargininemia with neurological impairment, highlighting its essential metabolic role 7.