Blockade of OPN in WT mice or macrophage depletion prevents the occurrence of PMN-dependent antibody-mediated TRALI in C57BL/6 WT mice. Lung W/D weight ratios (A,C) and percentage of pulmonary PMNs (B,D) in C57BL/6 WT mice primed with LPS, depleted of CD4⁺ T cells, injected with anti-MHC class I antibodies (clones 34-1-2s and AF6-88.5.5.3), either isotype-control antibody or anti-OPN antibody, and depleted of macrophages (C-D) or not (A-B). Statistical analysis was performed with a 1-tailed unpaired Student t test. Each dot represents 1 mouse, and error bars represent SD. *P < .05, ****P < .0001.