Soluble HLA class I, HLA class II, and Fas ligand in blood components: A possible key to explain the immunomodulatory effects of allogeneic blood transfusions

The immunomodulatory effect of allogeneic blood transfusions (ABT) has been known for many years. However, a complete understanding of the effects of ABT on the recipient's immune system has remained elusive. soluble HLA clas s I (sHLA-I), HLA class II (sHLA-II), and Fas ligand (sFasL) molecules may play immunoregulatory roles. We determined by double-determinant immunoenzy matic assay (DDIA) sHLA-I, sHLA-II, and sFasL concentrations in different b lood components. sHLA-I and sFasL levels in red blood cells (RBCs) stored f or up to 30 days and in random-donor platelets are significantly (P < .001) higher than in other blood components and their amount is proportionate to the number of residual donor leukocytes and to the length of storage. Bloo d components with high sHLA-I and sFasL levels play immunoregulatory roles in vitro as in allogeneic mixed lymphocyte responses (MLR) and antigen-spec ific cytotoxic T-cell (CTL) activity, and induce apoptosis in Fas-positive cells. These data suggest that soluble molecules in blood components are fu nctional. If these results are paralleled in vivo, they should be taken int o account in transfusion practice, blood components that can cause immunosu ppression should be chosen to induce transplantation tolerance, whereas blo od components that lack immunosuppressive effects should be preferred to re duce the risk of postoperative complications and cancer recurrence. (C) 199 9 by The American Society of Hematology.