Complement C3 is a core component of the complement system, consisting of alpha and beta polypeptide chains. C3 is mainly synthesized in the liver and is widely present in blood and body fluids. It plays a crucial role in immune responses, being activated through the classical, alternative, and lectin pathways to generate C3a and C3b fragments, which participate in inflammation, phagocytosis, and cell lysis. The activation and cleavage of C3 are central to the function of the complement system, influencing pathogen clearance and immune regulation. The expression of the C3 gene is specific in different individuals and tissues, and mutations or functional abnormalities are associated with the occurrence and development of various immune deficiency diseases, autoimmune diseases, and infectious diseases.