Mechanisms of transfusion-associated immunosuppression.
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Many studies have reported allogeneic blood transfusions to be associated with adverse effects in recipients. These include a variety of transfusion reactions, graft-versus-host disease, alloimmunization, the transmission of infectious agents, and immunomodulation. In some instances the immunomodulatory effect has been reported to be beneficial to the recipient, i.e., recipients of renal allografts, individuals with Crohn's disease, and women with recurrent spontaneous abortions. Recent evidence indicates, however, that this autologous blood transfusion-associated immunomodulation might adversely affect the prognosis in patients with a malignancy as well as increase their risk for postoperative bacterial infection. The mechanisms of the autologous blood transfusion-associated immunosuppressive effect remain ill defined, although recent evidence indicates that such effects are probably due to the infusion of allogeneic donor leukocytes, or their products, present in the cellular blood products used for the transfusion. Recent experimental animal data indicate that this autologous blood transfusion-associated immunomodulatory effect can be ameliorated by the prestorage leukodepletion of allogeneic blood. Although data from animal experiments are useful in defining various in vivo biologic activities, properly designed prospective clinical trials are required to provide definitive indications as to whether patients with a malignancy undergoing curative surgery should receive leukodepleted allogeneic cellular blood products and the appropriate timing for such leuko-depletion.