BLOOD-TRANSFUSION, BLOOD-STORAGE AND IMMUNOMODULATION

Allogeneic blood transfusion is the most frequent allotransplantation procedure performed on a routine basis with no prior HLA-typing. Rough ly 50% of the recipients of unprocessed red cells and platelets become alloimmunized. Evidence also exists for some degree of transfusion-in duced immunosuppression. Prior transfusion has been shown to enhance k idney transplant survival and evidence of an increase in tumor recurre nce and of infectious complications has also been presented. The prese nce of donor antigen-presenting cells appears to be a prerequisite for alloimmunization and they must be both viable and capable of presenti ng a costimulatory signal in order to induce IL-2 secretion and prolif eration of responding CD4 T cells. APCs presenting antigen but no cost imulatory signal can induce non-responsiveness in CD4 T cells, a possi ble mechanism of transfusion-induced immunosuppression. APCs in refrig erated blood continue to present antigen but progressively lose their ability to provide costimulation. By day 14 costimulatory capacity is absent and transfusion of such blood should not alloimmunize but could induce some degree of immunosuppression. Further refrigerated storage in excess of 2 to 3 weeks leads to induction of apoptosis in contamin ating leukocytes. We have found that alloantigens expressed on such ca lls do not appear to be recognized by responder T cells and transfusio n of blood stored in excess of 3 weeks should neither alloimmunize nor immunosuppress.