T Cells Binding to MHC-Peptide Complexes Are Responsible for Acceptance

question 51

Multiple Choice

T cells binding to MHC-peptide complexes are responsible for acceptance or rejection of transplanted organs.To facilitate acceptance of the transplant, the ideal donor will have a close genetic relationship with the recipient -- even then, immune suppression drugs are often necessary.In a strange variation of this phenomenon, the endangered Tasmanian devil of Australia suffers from a devastating disease in which tumorous tissue is transmitted from animal to animal.What is the likely explanation for the lack of rejection of this transmissible tumor?

• A)MHC genes are unique to humans.Without them, the T cells have no way to distinguish self and non-self.
• B)Marsupials lack an adaptive immune system.
• C)Low genetic diversity makes the MHC genes invariant, so the "transplanted" tissue is accepted as self.
• D)Tumors are never targeted by T cells, unless they are caused by a viral infection.

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