Used in immunological research to study T-cell activation and co-stimulatory signaling pathways. Serves as a ligand for CD28 and CTLA-4 receptors, enabling investigation of immune checkpoint mechanisms. Commonly employed in binding assays, protein-protein interaction studies, and ELISA development. The His tag facilitates easy purification and detection, making it valuable for in vitro assays and therapeutic antibody screening. Also utilized in structural studies to understand immune regulation at the molecular level.