PDCD1 and infection: Environmental triggers include medications (e.g., antibiotics, beta-blockers, non-steroidal anti-inflammatory drugs (NSAIDs), diuretics, dipeptidyl peptidse-4 (DPP-4 inhibitors), and immune checkpoint inhibitors targeting programmed cell death protein 1 (PD-1) and its ligand (PD-L1)), infections, vaccines, trauma, surgical interventions, burns, ultraviolet (UV) exposure, radiotherapy, and photodynamic therapy.