Major Histocompatibility Complex (MHC) relation to tissue transplantation

Question

Can anyone explain to me the role of MHC in tissue transplantation?

Answer 1

The immune system is highly complex. I personally would rate it in terms of complexity, second only to the brain itself

("Main article: major histocompatibility complex

group of genes that code for proteins found on the surface of cells that help the immune system recognize foreign substances. MHC proteins are found in all higher vertebrates. In human beings the complex is also called the human leukocyte antigen (HLA) system.

graft rejection

... important medical treatment. As are other forms of therapy, it is accompanied by certain risks. Each individual's cells have a spectrum of genetically determined cell surface protein antigens, the major histocompatibility complex (MHC) antigens, or human leukocyte antigens as they are referred to in humans. MHC antigens determine a person's tissue type just as red blood cell antigens determine ...")

See: MAJOR HISTOCOMPATIBILITY COMPLEX, OR MHC (GENETICS)

http://original.britannica.com/eb/topic-...

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It is my understanding of immunological function that---how well the HLA surface molecule on immune cells match up with MHC surface molecules on cells, tissues, and organs determine if an immune reaction (rejection) occurs or not.  The closer that HLA cell surface molecules match MHC surface molecules, the less likely that immune rejection will occur.

Also See: TRANSPLANT: From Myth to Reality

by Nicholas L. Tilney, M.D.

ISBN: 0-300-09963-0

Answer 2

First off, the answer above is totally incorrect.

An immunocompetent host recognizes the foreign antigens on grafted tissues (or cells) and mounts an immune response which results in rejection. On the other hand, if an immunocompromised host is grafted with foreign immunocompetent lymphoid cells, the immunoreactive T-cells in the graft recognize the foreign antigens on the host tissue, leading to damage of the host tissue and rejection.  The time of rejection also depends on the antigenic disparity between the donors and recipient. MHC antigens are the major contributors in rejection, but the minor histocompatibility antigens also play a role. Rejection due to disparity in several minor histocompatibility antigens may be as quick or quicker than rejection mediated by an MHC antigen. As in other immune responses, there is immunological memory and secondary response in graft rejection. Thus, once a graft is rejected by a recipient, a second graft from the same donor, or a donor with the same histocompatibility antigens, will be rejected in a much shorter time.

Histocompatible lymphoid cells, when injected into an immunocompromised host, are readily accepted. However, the immunocompetent T lymphocytes among the grafted cells recognize the alloantigens and, in response, they proliferate and progressively cause damage to the host tissues and cells. This condition is known as graft-versus-host (GVH) disease and is sometimes fatal.

To Christopher G above: I would suggest simply reading any immunology textbook that discusses MHC and graft/organ rejection. In fact, when I was in school, there was a whole semester class dedicated to xenotransplantation and immunological aspects regarding rejection. So, while you might be unhappy with my answer, fact is, your answer is wrong and easily proved by getting a copy of any immunology textbook on the subject. I'd recommend Janeway or Kuby.

Answer 3

Sorry, I'm not going to be able to answer your exact question, but histocompatibility is not an issue with tissue transplantation.  Generally, tissues are not vascularized, as transplanted organs are, and therefore are not subject to rejection.  Corneas are avascular and bone is processed into bone matrix (which is absorbed into the surrounding bone structure when transplanted).

Check this link for our industry trade group which may answer your specific question.

Response on 8/12/08:

Joe T, A bit more professional respect would have been appreciated, rather than simply dismissing my entire response as “totally incorrect.”  You are a virologist, and I am a transplant coordinator.  If my answer was oversimplified, I apologize, but my point is correct.  The question asked specifically about tissue transplants, which generally are not subject to rejection.  The major exception would be bone marrow transplant, which in many ways is more akin to organ than tissue transplantation.  This is where most discussion of graft vs. host disease centers around.  Bone marrow transplant is rare in comparison to the 1.5 million bone and other tissue transplants which take place each year (per CDC statistics).

The fact that corneas are avascular provides relative isolation from the body’s immune response, therefore rejection is not an issue.  The procedures for processing donated bone and most other tissue into forms usable by surgeons deactivates the antigens on the graft, therefore rejection is not an issue.  

As a last argument, know that I am also a tissue transplant recipient.  I received cadaver donor bone as part of a dental procedure.  While my HLA A and B typing is on file with the National Bone Marrow Registry, my dentist did not seek this information.  I was not typed or crossmatched for the allograft, and I was not monitored for rejection following the surgery.  How would your response explain that?