Methods of determination, polypeptide, method of identifying one or more tlp family members, isolated agent, methods of identifying or detecting one or more tlp family members and modulating immune system function and / or activity, anti-tigit antibodies, methods of modulating a cd226-pvr interaction, modulating immune cell function and / or activity, inhibiting an immune response, enhancing or stimulating an immune response, modulating the type and / or amount of cytokine production, stimulating erk phosphorylation, diagnosing a disease, assessing the severity of a disease, preventing a disea
