COPA (coat protein complex I subunit alpha) is a component of the COPI vesicle coat complex involved in intracellular protein transport. The protein functions primarily in retrograde vesicle-mediated transport from the Golgi to the endoplasmic reticulum, as well as in anterograde ER-to-Golgi and intra-Golgi vesicle-mediated transport. COPA localizes to the Golgi membrane, endoplasmic reticulum membrane, and cytosol, where it participates in maintaining proper protein trafficking through the secretory pathway. Mechanistically, COPA is a structural component of COPI coat complexes that facilitate vesicle budding and cargo transport between compartments of the secretory system. Mutations in COPA have been associated with autoinflammation and autoimmunity, systemic, with immune dysregulation, suggesting that disruption of intracellular protein transport through COPI dysfunction can compromise immune homeostasis. The disease association indicates that proper secretory pathway function, mediated by COPA, is critical for appropriate immune cell function and prevention of autoinflammatory responses. Understanding COPA's role in vesicular transport provides insights into how defects in fundamental cellular trafficking mechanisms can precipitate systemic immune dysregulation and autoimmune disease.