Blood transfusions (BT) should be considered as transplantation of blood elements. They evoke various alterations in the immune responsiveness of blood recipients, contributing to an increased risk of infection and cancer reccurrence. The exact mechanism by which blood transfusions induce a state of reduced immune responsiveness remains unclear. Relatively little isalso known about immune changes occurring in lymphoid compartments other than blood following blood transfusions. In the present study, the effect of syngeneic and allogeneic blood transfusions on hemopoiesis and immune responsiveness was examined in a rat model. Transfusions of both syngeneic and allogeneic blood caused an increase in the bone marrow myeloid and lymphoid lineage cell compartments as well as a rise in the percentage of OX7+ stem cells in bone marrow. It was followed by a release of OX7+ stem cells into blood circulation, higher in the case of rats transfused with syngeneic blood. The changes in hemopoiesis were accompanied by a diminished responsiveness of blood, spleen and bone marrow lymphocytes to mitogens in both groups of rats. Data point to early changes in distribution and reactivity of bone marrow and lymphoid cells following blood transfusion.

Keywords: Blood Transfusion, lymphocyte responsiveness, hemopoiesis