Used in immunological research to study the complement system, particularly the classical pathway activation. Enables detection and quantification of immune complexes in diagnostic assays. Employed in binding studies to identify interactions with antibodies, pathogens, or apoptotic cells. The His tag facilitates easy purification and immobilization on solid surfaces like nickel-coated plates or beads for ELISA, pull-down assays, and biosensor applications. Also utilized in structural and functional studies to understand innate immune responses and autoimmune disease mechanisms.