Apoptosis, TGF beta and transfusion-related immunosuppression: Biologic versus clinical effects.

Whether or not blood transfusion exerts an immunosuppressive effect on the recipient remains an area of controversy. The mechanism to clearly explain the effect has been elusive. We have previously suggested that there may be two categories of immunosuppressive transfusion effect: one which is HLA-dependent and directed against adaptive immunity and a second category which is mild, non-specific, and directed against innate immunity. This non-specific effect might result from the infusion of apoptotic blood cells. There is solid evidence that blood cells undergo apoptotic changes during refrigerated storage. The infusion of apoptotic cells has recently been shown in animal models to be immunosuppressive. Immunosuppression resulting from the infusion of apoptotic cells may be linked to transforming growth factor beta (TGF-beta).