It may seem counterintuitive that family members, who share genetic material, are often discouraged from donating blood to one another. Medical guidelines often recommend against direct blood donations between close relatives due to severe complications that can arise. This restriction lies in the human immune system and a serious reaction between donor and recipient cells.
The Primary Concern: Graft-versus-Host Disease
Direct blood donations between close family members are discouraged due to the risk of Transfusion-Associated Graft-versus-Host Disease (TA-GVHD). This rare, often fatal complication occurs when lymphocytes in the transfused blood recognize the recipient’s tissues as foreign and launch an immune attack. Symptoms, including fever, rash, liver dysfunction, and bone marrow suppression, often appear within 8 to 10 days. By then, widespread damage may have occurred. The mortality rate for TA-GVHD can be high, reaching up to 90%, making its prevention a high priority in transfusion medicine.
Why Genetic Similarity Increases Risk
The paradox of increased risk from genetically similar donors relates to Human Leukocyte Antigens (HLAs). HLAs are proteins on the surface of most cells, playing a fundamental role in the immune system’s ability to distinguish between “self” and “non-self.” While a close genetic match might seem beneficial, it can, in fact, create a dangerous scenario for TA-GVHD. When blood from a genetically similar relative, such as a parent, sibling, or child, is transfused, the donor’s lymphocytes might recognize the recipient’s HLA markers as “partially self.” This partial recognition means the recipient’s immune system may not fully recognize and eliminate the donor lymphocytes as foreign invaders. Instead, the donor lymphocytes can survive and become activated. This situation allows the donor’s immune cells to mount an attack against the recipient’s tissues without being effectively suppressed by the recipient’s own immune system, leading to TA-GVHD.
How Blood Safety Measures Address This Risk
Despite the risks, directed donations from family members can sometimes be performed under specific, controlled circumstances, particularly when patients have weakened immune systems due to conditions like chemotherapy, organ transplants, or congenital immunodeficiencies. To mitigate the risk of TA-GVHD in these situations, a specialized process called blood irradiation is employed. Blood irradiation involves exposing the donated blood unit to a controlled dose of radiation. This process specifically targets and inactivates the lymphocytes within the blood, rendering them unable to multiply and launch an immune response against the recipient. The radiation dose is carefully calibrated to destroy the problematic immune cells while preserving the function of other blood components, such as red blood cells and platelets, which are the intended therapeutic benefit of the transfusion. While irradiation is effective, it can reduce the shelf-life of the blood product. Blood banks and medical centers with specialized equipment often perform this procedure, ensuring the safety of directed donations when they are deemed medically necessary.