C3AR1 encodes the complement C3a receptor 1, a G protein-coupled receptor (GPCR) that binds the chemotactic peptide C3a and mediates inflammatory responses 123. Upon C3a binding, C3AR1 undergoes conformational changes triggering G(i)/G(o)-protein signaling that inhibits adenylate cyclase and modulates calcium-mediated signaling 2. C3AR1 is expressed on immune cells including macrophages, microglia, and neutrophils, where it regulates chemotaxis, granule enzyme release, and superoxide production 12. C3AR1 functions in multiple pathological contexts. In glioblastoma, hypoxia-induced C3a/C3aR signaling promotes M2 macrophage polarization and tumor aggressiveness; C3aR antagonism prolonged survival in preclinical models 4. During aging and neurodegeneration, endothelial C3AR1 signaling via intracellular calcium disrupts blood-brain barrier integrity and promotes vascular inflammation 5. In gastric cancer peritoneal metastasis, the C3-C3AR1 axis mediates stromal-myeloid crosstalk that confers immunotherapy resistance; axis blockade restored immunotherapy efficacy 6. C3AR1 also participates in cardiac regeneration, where C3a signaling between macrophages and fibroblasts assembles a pro-renewal cellular niche 7. Additionally, C3AR1 expression correlates with obesity severity, potentially linking complement signaling to metabolic dysfunction 8.