Used in immunological research to study complement system activation, particularly the classical pathway. Serves as a capture or detection reagent in immunoassays due to the Fc tag, enabling easy binding to anti-Fc antibodies or Fc receptors. Applied in protein-protein interaction studies involving immune complexes and autoantibodies. Also utilized in therapeutic antibody development to assess complement-dependent cytotoxicity (CDC) and evaluate antibody effector functions. The Fc tag allows for straightforward purification via protein A/G affinity chromatography.