BLOOD-TRANSFUSIONS DOWN-REGULATE HEMATOPOIESIS AND SUBSEQUENTLY DOWN-REGULATE THE IMMUNE-RESPONSE

BACKGROUND: Blood transfusions are associated with numerous clinical p henomena attributable to reduced posttransfusion immunocompetency. The exact mechanism by which blood transfusions induce a state of reduced immune responsiveness remains unclear. STUDY DESIGN AND METHODS: The effect of a large-volume blood transfusion on the frequency and respon siveness of immune cells in lymphoid compartments was examined in norm ovolemic rats. The effects of syngeneic and allogeneic blood transfusi ons were compared. RESULTS: The results in normovolemic rats were comp ared to those in nontransfused and saline-infused animals. In the norm ovolemic rats, there was a significant decrease in cells of erythroid lineage in bone marrow, with a slight increase in the percentage of ce lls in the bone marrow myeloid and lymphoid lineages; a significant in crease in the percentage of the OX7+ Thy1+ cell population in bone mar row cells (stem cells are contained in this population) and blood cell s; a decrease in the bone marrow OX6+ cell population (HLA class II-po sitive cells); a decrease in the responsiveness of blood, spleen, lymp h node, and bone marrow cell populations to mitogens; and a downregula ting effect of both syngeneic and allogeneic blood transfusions on hem atopoiesis and cell responsiveness. CONCLUSION: Massive whole blood tr ansfusion, either syngeneic or allogeneic, constitutes a strong downre gulating signal for hematopoiesis, affecting the erythroid, myeloid, a nd lymphoid cell lineages. It leads also to an attenuation of the resp onsiveness of hematopoietic tissues to mitogenic stimuli.