PDCD1 and nosocomial infection: Several studies reported that patients with septic shock and high levels of PD-1 expression on peripheral T lymphocytes were more likely to have an increased mortality and more occurrence of nosocomial infections [20] and Morrell et al. reported that PD-L1/PD-1 pathway-associated genes were significantly decreased in alveolar macrophages from ARDS patients who died or had prolonged mechanical ventilation [46].