The relation between aged blood products and onset of transfusion-related acute lung injury. A review of pre-clinical data.

Transfusion-related acute lung injury (TRALI) is the leading cause of transfusion related morbidity and mortality. TRALI is suggested to be a "two hit" event. The "first hit" is the underlying condition of the patient which results in sequestration and priming of neutrophils in the pulmonary compartment. The "second hit" is the transfusion of either human leukocyte antibodies or aged blood products which results in activation of the primed neutrophils and finally in pulmonary edema. The present review focuses on pre-clinical studies investigating the role of blood products containing aged cells (red blood cells, RBCs, and platelet concentrates, PLTs) and the onset of TRALI. Several mechanisms are under scrutiny. The first suggested mechanism is that soluble mediators accumulating during storage of RBCs and PLTs may play a role, including bio-active lipids or soluble CD40L. These soluble factors were found to cause lung injury in the presence of a "first hit". Another proposed mechanism involves the aged erythrocyte itself. During storage, the erythrocyte undergoes numerous changes in its biochemical and structural condition and acquires pro-inflammatory properties, sometimes collectively referred to as the "red cell storage lesion". Although it could be speculated that all of these factors may be involved in the onset of TRALI, only one pre-clinical study shows an association between the aged erythrocyte and the onset of TRALI. The suggested mechanism is a decrease in the chemokine scavenging function of the erythrocyte by reduction of the Duffy antigen expression resulting in an increase in lung injury. Further research is needed to elucidate possible mechanisms of onset of TRALI by aged blood products.