Immune effects of blood transfusion.

Blood is a complicated tissue that has been routinely applied over the past century. Since the recognition of the principles of species specificity (1818) and major compatibility for red cell antigens (1900), considerable attention has been given in the second half of this century to leukocyte-determined immune effects following transfusion. Most reactions are febrile and nonhemolytic and show, in limited situations, true relation to immune activity of transfused white blood cells. The complete picture is not yet finished; however, the more important immune effects are stimulation and modulation, tolerance and suppression. Here most work done is ex vivo and in animal experiments. Little clinical evidence has been obtained or assessment done. Most publications therefore relate to laboratory work, extrapolating results to the bedside. The most interesting publication over the review period with regard to the core immune effects of blood transfusion relates to measured concentrations of active, soluble molecules like HLA class I and II and Fas ligand molecules and to their in vitro immunomodulating effect as well as effects on induction of apoptosis. Stored red cell preparations show an increase in soluble molecules and death of viable leukocytes. Platelet preparations show similar phenomena, although information on numbers of white blood cells and storage conditions are lacking. The authors propose selective use of these aged components in specific clinical settings to allow immune suppression, induction of cell anergy, and apoptosis, whereas fresher products not showing increased levels of soluble molecules could be applied in clinical settings in which immunosuppression is not wanted. No reference is found to scientifically support and substantiate the global universal leukodepletion movement.