Leucodepletion and immune response mechanisms

The recipient and donor mechanisms responsible for mediat-ing alloimmunity and immunomodulation during bloodtransfusions are complex and most probably superimposedthus creating multilevel elds of potential interaction andregulation. For example, at the recipient level, both the innateand adaptive immune systems can be signicantly affectedby various types of transfusions [1,2]. In addition, the healthstatus of the recipient plays a critical role in determining howthe host will immunologically respond to transfusion. On theother hand, donor transfusion products have many charac-teristics that can potentially inuence recipient immunityand its regulation (e.g. age, leucocyte content, etc.). Under-standing how these varied parameters culminate in an immuneresponse or not is fundamental to developing safer bloodproducts and better care for recipients.Many prospective randomized studies have shown thatleucoreduction of blood components can reduce the incidenceof alloimmunization and platelet refractoriness [3]. Mainlybased on these data, leucoreduced components are now re-commended for any patient requiring long-term transfusionsupport such as patients with leukaemia, lymphoma, myelo-dysplasia or those undergoing stem cell transplantation.Although leucoreduction has shown a clear benet by reduc-ing the incidence of alloimmunization and refractorinessin these immunocompromised patient groups, it is not clearhow leucoreduced blood products may affect the immuneresponse in immunocompetent individuals such as trauma orsurgical patients. However, in a recent randomized controlledstudy with 404 cardiac surgery patients, a single multiunittransfusion of either leucoltered RBC (stored or not) or buffycoat-reduced RBC induced similar levels of anti-HLA allo-immunization [4]. These results suggest that not all patientgroups may benet from leucoreduced blood products andother treatment modalities may need to be developed to reducealloimmunization in those patients. Understanding the immuneresponse against leucoreduced blood products in healthyrecipients can be accomplished by studying animal modelsof transfusion. This paper will focus on how, in healthyrecipients, leukoreduction may have a ‘double-edged sword’effect on alloimmune mechanisms.