Used in immunological research to study immune checkpoint pathways, particularly the PD-1/PD-L1 interaction that regulates T-cell activation and immune tolerance. Employed in assays such as ELISA, flow cytometry, and surface plasmon resonance to detect binding activity and screen potential inhibitors. Serves as a critical reagent in developing monoclonal antibodies and immunotherapies for cancer, autoimmune diseases, and chronic infections by modulating immune responses. The Fc tag facilitates detection, purification, and enhances stability in experimental systems.