This article provides a review of the role of PD-1 signaling in health and immune-related diseases, including tumor immunity, autoimmunity, infection immunity, transplantation immunity, allergy, and immune privilege, as well as immune-related adverse events (irAEs) of anti-PD-1 and anti-PD-L1 drugs (Figure 1). The gene discussed is PDCD1; the disease is Autoimmunity.