PDCD1 and Sepsis: Immune checkpoints constitute a complex array of receptors (e.g., PD-1, CTLA-4) and their ligands (e.g., PD-L1/PD-L2, CD80/C86) expressed on both innate and adaptive immune cells, which exert key regulatory roles during homeostasis and inflammatory pathologies, mainly in chronic infection, sepsis and cancer.