SAA2 (serum amyloid A2) is a major acute phase reactant synthesized primarily in the liver, comprising a conserved 104-amino acid protein family member alongside SAA1 1. During acute inflammatory responses to trauma and infection, serum SAA2 levels rise dramatically 1. SAA2 functions as a lipophilic protein contributing to HDL and cholesterol transport 1, while also acting as a retinol-binding protein that delivers vitamin A to intestinal myeloid cells via LRP1-mediated endocytosis, promoting adaptive immunity and immunoglobulin A production 2. Mechanistically, SAA2 modulates immune responses by directing pathogenic Th17 cell differentiation through direct T cell signaling in collaboration with STAT3-activating cytokines 3. In intestinal epithelial cells, C/EBPA-driven SAA2 production promotes Th17 differentiation 4. SAA2 expression is upregulated in the mesentery during inflammatory bowel disease, contributing to macrophage immunoregulation 5. Notably, SAA2 shows disease-protective functions, with high expression in normal hepatocytes and reduced expression in hepatocellular carcinoma tissues, where it acts as a tumor suppressor 6. These multifaceted roles position SAA2 at the intersection of host defense, metabolic regulation, and immune homeostasis, with implications for inflammatory and malignant disease management.