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Lecture notes – They recognise the graft
Biology (C100)
University of Salford
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Lecture notes – They recognise the graft
Cytotoxic T cells then recognize the graft because it bears foreign class I MHC molecules. This response is much like the activation of CTLs by virally infected host cells. A second mechanism involves the T-helper cells reacting to the graft and releasing cytokines. The cytokines stimulate macrophages to enter, accumulate within the graft, and destroy it. MHC molecules play a dominant role in tissue rejection reactions because of their unique association with the recognition system of T cells. Unlike antibodies, T cells cannot recognize or react directly with non-MHC molecules (viruses, allergens). They recognize these molecules only in association with, or complexed to, an MHC molecule.
Tissue Transplantation Rejection
Because class I MHC molecules are present on every nucleated cell in the body, they are important targets of the rejection reaction. The greater the antigenic difference between class I molecules of the recipient and donor tissues, the more rapid and severe the rejection reaction is likely to be. Class II MHC molecule mismatch can also result in rejection and may be even more severe than class I mismatch reactions. However, the reaction can sometimes be minimized if recipient and donor tissues are matched as closely as possible. Most recipients are not 100% matched to their donors, so immuno suppressing drugs are used to prevent host mediated rejection of the graft.
Organ transplant recipients also can develop graft-versus host disease. This occurs when the transplanted tissue contains immune cells that recognize host antigens and attack the host. The immuno suppressed recipient cannot control the response of the grafted tissue. Graft-versus-host disease is a common problem in bone marrow transplants. The transplanted bone marrow contains many mature T cells. These cells recognize the host MHC antigens and attack the immunosuppressed recipient’s normal tissue cells.
In November 2002 a mysterious pneumonia was seen in the Guangdong Province of China, but the first case of this new type of pneumonia was not reported until February 2003.
Thanks to the ease of global travel, it took only a couple of months for the pneumonia to spread to more than 25 countries in Asia, Europe, and North and South America.
This newly emergent pneumonia was labeled “severe acute respiratory syndrome” (SARS), and its causative agent was identified as a previously unrecognized coronavirus (CoV), the SARS-CoV.
Almost 10% of the roughly 8,000 people with SARS died.
SARS-CoV
However, once the epidemic was contained, the virus appeared to “die out,” and with the exception of a few mild, sporadic cases in 2004, no additional cases have been identified.
From where does a newly emergent virus come? And why did this viral disease apparently disappear?
Coronaviruses are large, enveloped viruses with positive strand RNA genomes. They are known to infect a variety of mammals and birds.
Researchers suspected that SARS-CoV had “jumped” from its animal host to humans.
To test this hypothesis, samples of animals at open markets in Guangdong were taken for nucleotide sequencing.
These studies revealed that cat like animals called masked palm civets (Paguma larvata) harbored variants of the SARS-CoV.
Lecture notes – They recognise the graft
Module: Biology (C100)
University: University of Salford
