The antibodies in question attack a naturally occurring antigen called MICA, which is found in endothelial cells. The endothelium is the layer of cells lining the inside of the blood vessels. Each person has one or two of the more than 60 varieties of MICA antigens currently known. “When you put a transplant in, the blood of the new host comes into contact first with the endothelium of the donor organ. That´s where the host first meets the donor and where rejection starts,” said Dr. Peter Stastny, professor of internal medicine, chief of transplant immunology at the UT Southwestern Medical Center and an author on the study.

“The bottom line is that the data suggests that failure of otherwise well-matched kidneys may be caused by these antibodies. We are not saying that all such kidneys fail because of antibodies against MICA, but this may be part of it,” he said.

UT Southwestern researchers became interested several years ago in the possibility that there might be some antigens in the kidney that were not present on lymphocytes, which are the cells used for typing and cross-matching for kidney transplants. “If the antigens are not present on the lymphocytes, then the usual lymphocyte cross-match would not detect such antibodies,” Dr. Stastny said.

Researchers first had to confirm that the antigens were present in the kidneys, then follow enough cases to determine whether the antibodies against MICA antigens correlated with rejection of otherwise healthy kidneys. “We found that there was a strong correlation. The presence of the antibodies against MICA was associated with earlier rejection of the kidney grafts. It doesn´t prove that the antibody causes the rejection, but it suggests it,” Dr. Stastny said. In addition, researchers discovered that the patients who were considered a good risk in clinical transplantation were the ones who showed the most marked effect of these antibodies against MICA.; Source: UT Southwestern Medical Center