Used in immunological research to detect and quantify C4a, a complement system activation marker, in biological samples such as serum or plasma. Helps in studying allergic reactions, immune complex diseases, and conditions involving complement system dysregulation like lupus, sepsis, and autoimmune disorders. Supports investigation into the role of the complement cascade in inflammation and hypersensitivity responses. Commonly applied in clinical research and pharmaceutical development to assess complement activation pathways and evaluate therapeutic interventions targeting immune responses.