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Transfusion-Related Immunomodulation
Transfused blood products may have effects on recipient immunity. Broadly, these effects have been called transfusion-related immunomodulation (TRIM). Some TRIM effects are generally accepted, while others are a matter of debate. The TRIM effects can be categorized as beneficial or deleterious ( Table 71.1 ). The following effects are more evident with blood that has not been leukoreduced.
Table 71.1
Established and Proposed Transfusion-Related Immunomodulation Effects
| Decreased renal allograft rejection |
| Improvement in autoimmune diseases (e.g., Crohn’s disease) |
| Decreased repetitive spontaneous abortions |
| Increased tumor recurrence |
| Increased postoperative infection |
Accepted Transfusion-Related Immunomodulation Effects
Solid Organ Transplantation
Since the 1960s, it has been appreciated that transfusion of whole blood before organ transplantation results in significantly improved allograft survival in both humans and experimental animals. This effect was most notable for transplanted cadaveric kidneys. This phenomenon, or “transfusion effect,” occurs to the greatest extent with the transfusion of whole blood, and to a lesser extent with RBC products. Leukocytes appear to play a central role in this process, as there is little effect with washed RBC products (∼80%–90% leukocyte reduced) and essentially no transfusion effect when giving leukoreduced products (99.9% leukoreduced). The transfusion effect appears to be antigen specific, leading to tolerance to HLA antigens. There is a strong correlation between improved allograft survival and coincidence of HLA antigens on the donor organ and on the transfused white blood cells. This is especially true for the HLA-DR locus; a mismatch results in increased sensitization, and a partial mismatch results in the transfusion effect. However, transfusion also carries the risk of sensitization to HLA antigens. The formation of HLA antibodies can cause acute humoral rejection of the allograft and therefore the majority of transplants do not use crossmatch-incompatible allografts (i.e., HLAs present on the allograft for which the recipient has HLA antibodies). Current immunosuppressive medications have greatly reduced the benefits of the transfusion effect. Thus, current practice is to provide potential transplant recipients (particularly kidney and heart transplantation) with leukoreduced products to prevent HLA alloimmunization.
Decreased Likelihood of Recurrent Spontaneous Abortions
It has been observed that transfusion of allogeneic blood, from paternal or other sources, has a beneficial effect in preventing recurrent spontaneous abortion in women possibly by decreasing the T-cell response and generating suppressor T cells. Although the effect is mild, it is reproducible.
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