The ability of the immune system to respond appropriately to foreign antigen is dependent on a delicate balance of activating and inhibitory signals. Although positive signaling is essential for the generation of effective immunity, counterbalancing the immune response by inhibitory pathways is equally important. Loss of inhibitory signaling is often associated with autoreactivity and unchecked inflammatory responses, illustrating the essential role these systems play in immune regulation (Ref.1). Pairing of activation and inhib...