PDCD1 and Sepsis: Moreover, studies involving sepsis mouse models and patients with sepsis have reported increases in the expression of coinhibitory receptors, such as programmed cell death protein-1 (PD-1), TNF-related apoptosis-inducing ligand (TRAIL), B and T lymphocyte attenuator (BTLA), and lymphocyte activation gene-3 (LAG-3), in T cells (23–25), partly explaining the persistent reduction in proliferative capacity and inflammatory cytokine production.