The exact mechanism of lung injury in transfusion-related acute lung injury (TRALI) has not be identified. It is believed that the mechanism may vary from patient to patient. The most common finding is leukocyte antibodies in donor or patient plasma.
Anitbodies to human leukocyte antigen (HLA) have been associated with TRALI. These anti-HLA antibodies can be formed in response to exposure to foreign antigens from transfusion or pregnancy. The source of the antibody is usually the donor, not the patient. Transfused antibodies react with the recipient which results in leukocyte emboli aggregating in the lung capillary bed. Capillary damage triggers interstitial edema and fluid in the alveolar spaces, causing decreased air exchange and hypoxia.