Direct antibody-mediated TRALI. Priming events may or may not be required for antibody-induced TRALI, but appear to significantly exacerbate TRALI when present. Transfusion of blood products containing antibodies against HNA and MHC class I can result in direct activation of intravascular neutrophils. Anti-MHC class I antibodies recognizing endothelial MHC class I may also directly tether neutrophils to the endothelium independent of selectin or integrin-mediated events. Immune complexes of anti-HNA or anti-MHC class I and soluble HNA or MHC class I may also be recognized by Fc receptors resulting in neutrophil activation. Intravascular activation of neutrophils results in damage to endothelial cells, vascular leakage and pulmonary edema.