Which one of the following statements about T cell tolerance to self proteins is accurate?
A)Self proteins are not presented by the class I pathway because only microbial proteins,and not self proteins,are ubiquinated in the cytosol.
B)Peptides derived from self proteins are not presented by the class I or class II pathways because MHC molecules are expressed only in response to infections.
C)Self proteins are not presented by the class II pathway because endosomal acidic proteases digest microbial proteins but not eukaryotic proteins.
D)Self peptide/self MHC complexes are formed and displayed by antigen-presenting cells in both class I and class II MHC pathways,but T cells that recognize these complexes usually are not present or are functionally inactive.
E)Peptides derived from self proteins are not displayed by MHC molecules because they usually are displaced by the more abundant microbial peptides.

Question

Quizplus · Accepted Answer

T cell tolerance is a result of deletion or inactivation of self-reactive T cells.The various steps in both the class I and the class II MHC antigen-presenting pathways do not discriminate between self and microbial proteins.Although expression of MHC molecules is up-regulated as a result of the innate immune responses to infections,there is some degree of constitutive expression of class II MHC on professional antigen-presenting cells,and class I MHC is constitutively expressed on most cells in the body.Only a small fraction of the surface MHC molecules of an infected cell will express peptides derived from microbial peptides.

Which One of the Following Statements About T Cell Tolerance