Expression of Fas and Fas ligand on spleen T cells of experimental animals after unmodified or leukoreduced allogeneic blood transfusions.

BACKGROUND: The clonal deletion seen in recipients of allogeneic blood transfusion (ABT) refers to the removal of lymphocytes that promote the clearance of transfused alloantigens. Interactions between Fas (CD95) and FasL (CD95L) are involved in the clonal deletion of T cells and in the down regulation of the cytotoxic T-cell activity. STUDY DESIGN AND METHODS: The expression of CD95/95 L on spleen T cells of C57Bl/6 mice infused with unmodified ABT, prestorage leukoreduced ABT (LR-ABT), or saline was investigated by flow cytometry. The numbers of apoptotic spleen cells were evaluated after transfusion using the acridine orange and ethidium bromide uptake technique. RESULTS: Compared with untransfused animals, mice transfused with ABT showed higher expression of CD95 (MFI = 94.4 ± 8.6 vs. 73.1 ± 7.9, p = 0.02) and CD95L (23.5 ± 6.9 vs. 8.1 ± 2.0, p = 0.008) on CD4+ spleen cells. Expression of CD95 (92.2 ± 7.5 vs. 64.9 ± 7.5, p = 0.007) and CD95L (17.7 ± 3.6 vs. 8.2 ± 2.2, p = 0.02) was also increased on CD8+ cells of these animals. CD8+ spleen cells from mice transfused with ABT showed higher expression of CD95 (92.2 ± 7.5 vs. 76.9 ± 4.0, p = 0.03) and CD95L (17.7 ± 3.6 vs. 8.3 ± 1.5, p = 0.03) than cells from mice transfused with LR-ABT. The number of apoptotic spleen cells from mice transfused with ABT was greater than that from mice infused with LR-ABT (10.9 ± 1.3 vs. 6.6 ± 1.8, p = 0.01) or saline (10.9 ± 1.3 vs. 6.5 ± 0.7, p = 0.001). CONCLUSIONS: The data suggest that ABT up-regulates the expression of Fas/FasL on spleen T cells of mice and may promote their apoptosis. These ABT-associated immunologic alterations can be partially prevented by the leukoreduction of the transfused blood.