SPDL1 and acute respiratory distress syndrome: Given that sPD-L1 was reported to retain its receptor-binding domain with PD-1 and could deliver immunosuppressive signals as membrane PD-L1, we used Fc-conjugated programmed death ligand 1 (PD-L1-Fc) protein to mimic sPD-L1 and investigate the function of PD-L1 in ARDS mice.