Blood, Tissue, HLA Matching
First, let’s get two definitions out of the way:
Antigen: An antigen is any substance that causes an immune response, specifically the production of antibodies. Examples of antigens: pollen, virus, bacteria, toxins, foreign blood cells.
Antibody: A blood protein produced by the body when it recognizes a substance as alien (not natural) to the body. The antibody’s purpose is to counteract the foreign substance’s antigens.
When we talk about an organ being a “match” or a living donor being a “match”, we’re actually referring to three separate things:
1. Blood type compatibility
2. HLA (Human Leukocyte Antigen) or Tissue Matching
I. Blood type matching
Blood type compatibility is easily determined. In fact, when a person contacts a transplant center to express interest in donating a kidney or liver, one of the initial intake questions is about blood type. Not all blood types can donate to, or receive an organ from all other blood types. If a potential living donor cannot donate to their recipient of choice due to incompatible blood types, the transplant center may ask the potential living donor if s/he is willing to participate in a pair, swap or chain. It is perfectly acceptable to say NO. The transplant center cannot disclose this decision to anyone, including the intended recipient.
II. HLA or Tissue Matching
All humans possess six Human Leukocyte Antigens, a set of three from each parent, which reside on each gene (XX or XY). There are three general groups of HLA: A, B & DR with many subsets of each (238, 239). Some of these subsets (alleles) are more common than others, and their prevalance varies across geography and population (240).
The would-be recipient and the potential donor’s blood are HLA typed and then compared. The results are given as “X out of 6” match.
Some transplant professionals claim that HLA match is no longer important. It’s true that short-term (3 year) graft (organ transplanted) survival is less affected by the degree of the match, but the greater the match, the longer, on average, the transplant will last. In addition, certain mis/matches (eg. 0-1 B vs 2 or more B mismatch) have a greater effect on long-term graft survival than others (242).
Also, the greater the mismatch, the more anti-rejection medications the recipient will have to take to stave off rejection. These medications can increase a person’s risk of cancer-related death up to 10 times that of the general population (234).
SRTR (the Scientific Registry for Transplant Recipients) analyzes and publishes data from U.S. transplant centers. Under “Researchers” and “Data Tables”, choose the organ of interest (eg. kidney) to find a list of tables. Look for “Level of HLA mismatching”
Indepth article on HLA matching and graft survival in kidney transplantation.
Antibodies attach themselves to the part of the antigen known as an epitope. Each HLA has multiple epitopes. Researchers are discovering that some HLA mismatches are tolerated better than others because some epitopes provoke the development of antibodies, and others do not (248). There is a growing movement to tissue match to the epitope rather than simply to the antigen. Don’t be afraid to ask your transplant center about their method of tissue matching.
A very small amount of the potential donor’s blood is mixed with the recipient’s blood to determine if the recipient’s antibodies will attack the potential donor’s blood, and subsequently, any organ from that donor. A “negative crossmatch” indicates the donation can take place.
More information from the University of Michigan Medical Center.
If blood type is compatible, crossmatch is negative and HLA achieves minimum level, the potential living donor will have to decide if s/he wishes to submit herself to two days of diagnostic testing, the purpose of which is to A. determine if the donor is healthy enough to survive the procedure and live a normal life post-donation, and B. if the prospective donor organ is healthy enough to keep the intended recipient alive.
Many prospective donors who find themselves unable to continue the process experience sadness or even profound depression, anger, disappointment and helplessness. This is completely normal. It is important to remember that no one blames you for being unable to donate, and your willingness to give a (literal) part of yourself to help someone else is magnificent and admirable. While there are very few, if any, real life support groups for living donors, there are forums and email lists online that, hopefully, can provide you with consolation, information, reaffirmation and respect.
Feel free to email LD101 as well.
|Kidney Swap or Kidney Paired Donation: When two incompatible donor-recipient pairs are “swapped” to faciliate two transplants. In other words, potential living donor A is incompatible with would-be recipient A; likewise for|
If your blood type and that of the recipient’s are incompatible, there are programs available to facilitate Paired Exchanges, which means you and your recipient are matched up with another donor/recipient pair who also have incompatible blood types. Sometimes these exchanges involve multiple donor/recipient pairs.
Websites are popping up to facilitate what is known as “Good Samaritan” or “non-directed” living donation, which allow those in need of an organ to advertise for a living kidney donor. These sites operate outside of UNOS/OPTN legal jurisdiction, meaning there is no oversight or guidelines to protect either the recipient or the kidney donor. In addition, these sites charge a fee to the recipient for listing. Just because a site is ‘non-profit’ does not mean they aren’t taking home a paycheck. If you are interested in donating to a stranger, please contact your local transplant center.
Please see our Facts page for the controversy surrounding these sites.
Glomerular Filtration Rate – in layperson’s terms, it’s how kidney function/effectiveness is measured.