EMQ 11. Theme: Initiation of an immune response.

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From the options below, identify the most appropriate response to the question "Will this cellular event trigger an immune response" for each of the events listed.

A No, because no novel peptide is presented to patrolling T cells.
B Yes, because B cells and CD4+ T cells (helper T cells) will be activated.
C Yes, because CD8+ T cells (cytotoxic T cells) will be activated.
D Yes, because peptides beginning with formyl methionine activate the immune system.

1.Cell lysis that releases cytosolic proteins, encoded by the cell’s own genome, but never before found in the extracellular medium.
Your Answer:
Answer: A, No, because no novel peptide is presented to patrolling T cells. Although the entire protein may never have appeared in the extracellular medium before, peptides generated by proteolysis of the protein will have been presented on the surface of any cells expressing it throughout the life of the organism. No CD4+ T cells will therefore be activated by peptides presented by B cells whose antibodies bind the protein (see figure 19.8 on book page 324) so the B cell will not be activated.
2. Cell lysis that releases proteins encoded by mitochondrial genes into the extracellular fluid.
Your Answer:
Answer: D, Yes, because peptides beginning with formyl methionine activate the immune system. This is directly discussed in example 8.1 on book page 128, but is also mentioned in the main text on page 278 in Chapter 16. The fact that mitochondrial proteins can activate the immune system is discussed on ths web site {link to Chapter 8 / Web text box / More on the irritating formyl methionine}.
3. Folding of a cell surface protein into a novel shape, e.g. as a result of a change of extracellular pH.
Your Answer:
Answer: A, No, because no novel peptide is presented to patrolling T cells. See book page 323.
4.Production of proteins encoded by the genome of an infecting virus.
Your Answer:
Answer: C, Yes, because CD8+ T cells (cytotoxic T cells) will be activated. Peptides generated from the viral proteins will be presented on the surface of the infected cell on major histocompatibility complex proteins. Because they are novel, they will activate patrolling CD8+ T cells. See book page 322.
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