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I read somewhere that recently some people are trying to use harmless bacteria that live symbiotically in humans to express some portions of antigens of the harmful ones. Some people have raised concern that continuous exposure to the same antigen may lead to adaptibility of immune system to that epitope and render it useless when the germ actually comes.

Can't we use the same procedure for exposing some parts of MHC of the donor to the recipient before transplantation, so that, by the time the real transplant is done it may become adapted ? How much time would it take for this to occur ?

I can already see one drawback : In emergency transplants, this can not be used due to time factor. Can you see any other drawbacks ?

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A patient needing an organ transplant, even if it is not an emergency, is usually seriously ill. Triggering a potentially severe immune reaction is not a good idea for them. If you would manage to trigger an adaption in some patient, this does not mean that it will always work. So you need a (error save) method, to check for adaption, because non adapted patients will need immune repression before transplanting the organ. –  skymninge Sep 12 '13 at 13:24
I don't know how long the adaption process would take, but it will only be possible for transplants from living donors, because it will sure take a lot longer than an organ can be kept alive. –  skymninge Sep 12 '13 at 13:27
@skymninge I am saying that this can be used complementary to the "traditional" way. If patient gets adapted, then good otherwise go with the conventional way. –  biogirl Sep 12 '13 at 16:42
@skymninge I like the first point in your comment - triggering an immune response in the already sick patient will be not so good. –  biogirl Sep 12 '13 at 16:44
Do you have a link to the place you read that? –  Amory Sep 12 '13 at 16:55
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No. MHC works differently from any other antigen. MHC is involved in the maturation of T lymphocytes in the thymus. Forming lymphocytes need to recognise the MHC with a certain affinity (lymphocytes with too much affinity for the MHC are destroyed). In all this process there is no intervention of foreign antigens, so the system you propose won't work because the lymphocytes would search the MHC of the graft and they would attach them with abnormal affinity. This would trigger autoimmune response.

What you propose is the main functioning of allergy vaccines. You expose the immune system to low dose of antigen during long time, and that would make the body to not react aggressively to the substance. However, this phenomenon is based in B lymphocytes, which recognaise soluble antigens and little cells (humoral immune system) instead of whole cells (cellular immunity).

In the domains of science fiction, however, it would be technically possible to transfect thymal cells in order to express the MHC of the donor, since it would express both. Actually, this should be theoretically easy (The thymal cells seems to express almost any protein in the body, in order to prevent autoimmunity), but it face the problem of thymal degeneration.

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Angel Naranjo Oritz : Just wondering, why are lymphocytes with too much affinity for MHC destroyed ? –  biogirl Sep 12 '13 at 16:45
Could you explain the first paragraph more elaborately ? I am not able to understand your idea.Thanks ! –  biogirl Sep 12 '13 at 16:52
@biogirl If there is too strong of an affinity for the MHC complex, the lymphocytes may be able to bind outside of the specific MHC:antigen context; in particular it may allow them to react to self-peptides, resulting in autoimmunity. –  Amory Sep 12 '13 at 16:53
@Amory I may be wrong but what I understood is - If lymphocytes bind too strongly to new MHC , they may also trigger autoimmunity ????? –  biogirl Sep 12 '13 at 16:56
Exactly. MHC function is to "show" internal peptides to the immune system. When this peptids are alien, the lymphocyte assumes that the presenting cell is infected by a virus or a bacteria, and try to destroy it. There is a double check that ensures the lymphocyte attach the MHC and also that it can separate. If an alien peptide is present in the system, the second check doesn't trigger, and instead the lymphocyte will induce apoptosis. –  Miguel Ángel Naranjo Ortiz Sep 12 '13 at 16:59
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