Evidence behind the pathophysiology of TRALI

Transfusion-related acute lung injury (TRALI) is a serious transfusion complication that may lead to significant morbidity and mortality. This has driven a significant research effort focused on understanding why and how TRALI develops. The ultimate goal must be prevention or at least mitigation of the clinical consequences of TRALI. The underlying pathophysiology of TRALI is presently best described by two hypotheses which are not mutually exclusive. These are the antibody mediated TRALI mechanism and the two-event or priming TRALI mechanism. One of the key initial findings in TRALI research was the frequent presence of leucocyte antibodies in associated blood products, providing strong evidence for an antibody driven pathogenesis. In contrast, the two-event mechanism proposed that these transfused antibodies activated neutrophils that had first been primed by the patient’s clinical condition. Together, data from haemovigilance programs, clinical reports and experimental findings have led several countries to introduce TRALI risk-reduction strategies. These include either limiting the transfusion of plasma from female donors or, screening female donors for the presence of leucocyte antibodies. Both approaches are justified by adoption of the immune mechanism as the prime driver of the pathogenesis of TRALI. TRALI incidence has gratifyingly been reduced by these measures. Nevertheless, TRALI cases persist and they remain a major concern because of continuing significant morbidity and mortality. While the majority of earlier TRALI research has focused on the role of antibodies in TRALI, evidence for the role of non-antibody factors in TRALI is now growing, based on an increasing number of in vitro, ex vivo and in vivo models. This review aims to present data from such models, which are the foundation for our current understanding of the pathophysiology behind antibody mediated and non-antibody mediated TRALI.