Involved in negative regulation of immune response. Acts upstream of or within negative regulation of apoptotic process; negative regulation of tolerance induction; and positive regulation of apoptotic process. Located in external side of plasma membrane. Is expressed in retina. Used to study dilated cardiomyopathy and systemic lupus erythematosus. Human ortholog(s) of this gene implicated in autoimmune disease (multiple); hepatitis B; hepatitis C; hepatocellular carcinoma; and lupus nephritis. Orthologous to human PDCD1 (programmed cell death 1). [provided by Alliance of Genome Resources, Apr 2022]