Approximately 20% of individuals who suffer a traumatic injury require a blood transfusion; of these, 10% to 15% experience a condition known as transfusion-associated microchimerism. This occurs when white blood cells, or leukocytes, from the donor's blood persist in the recipient long after the transfusion occurs. The genetically distinct donor cells can remain in the individual for decades, and may account for as many as 4% of the white blood cells in the recipient's body. This suggests that the donor cells are tolerated by the recipient's immune system. The purpose of this study is to examine the specific factors that predispose some blood transfusion recipients to develop microchimerism.

In this study, blood samples will be collected from injured individuals who arrive at the University of California at Davis Medical Center. Individuals who receive a blood transfusion, as well as a control group of individuals who do not receive a transfusion, will be approached to enroll in the study.

Individuals who agree to participate will have their blood collected at Days 7, 14, and 28 and Months 3 and 6. Study researchers will analyze the blood for evidence of microchimerism. Participants with microchimerism will undergo additional blood collection at Months 12, 18, 24, 30, and 36. Information will be collected from all participants on health status, injury characteristics, hospital care, blood transfusion details, and blood donor characteristics.