OPN mediates TRALI via stimulation of pulmonary neutrophil accumulation. The infusion of anti-MHC I antibodies triggers TRALI. OPN is released by macrophages, potentially as a result of the presence of anti-MHC I, and in its polymerized form, it accumulates in lungs. OPN in the lungs acts as a potent neutrophil chemoattractant. The efflux of neutrophils in lungs mediates TRALI.