Programmed cell death protein 1 (PD-1) is a cell surface receptor on immune cells and plays an important role in regulating the immune system. PD-1 helps to prevent autoimmune diseases by suppressing specific immune cells. However, PD-1 may also contribute to the development of tumors when it interacts with the ligand, PD-1L, present on cancer cells. Because of this, PD-1 has become an important target for many cancer immunotherapy drugs. Signosis’ Human PD-1 ELISA kit can accurately measure PD-1 levels in human samples and provides a human PD-1 protein standard for quantitative analysis.