Transfusion and recipient immune function.

For some time it has been known that allogeneic blood transfusions have immunologic effects on animal and human recipients. These effects include increased numbers of suppressor T cells, decreased natural killer-cell function, decreased function of macrophages and monocytes, induction of anti-idiotypic antibodies that suppress allogeneic antigen recognition, and decreases in alloreactivity of mononuclear cells in mixed lymphocyte cultures. The meaning of these changes is not clearly understood, nor is the exact clinical importance of these alterations known. However, these decreases in immunologic function may explain a number of clinical consequences some investigators believe are the sequelae of homologous blood transfusions. Clinically important outcomes that are associated with transfusions are improved survival of renal allografts and increased risks of bacterial infection and cancer recurrence after perioperative transfusions. Transfusion of plasma-rich blood components (eg, whole blood) has been specifically associated with earlier cancer recurrence and better renal allograft survival in some patient groups. The new hypothesis that transfusion of stored plasma is a major factor in altering host immune defenses is supported by the observation that patients infected with human immunodeficiency acquired immunodeficiency syndrome more rapidly if they have been transfused with large amounts of plasma. Contrary to previous belief, the transfusion of homologous stored blood plasma may have as great or greater effects on immunity than transfusion of white blood cells. We believe investigation into the immunologic effects of transfusions is likely to have a significant impact on transfusion medicine research and practice over the coming years.