EMQ 12. Theme: Cell:cell interactions in the immune system

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From the options below, identify the most likely immediate outcome of the situations listed.

A Activation of immune system cells and triggering of apoptosis in cell X.
B Activation of immune system cells, cell X continues its normal role, neither undergoing apoptosis not proliferating.
C Activation of immune system cells, cell X initiates cell division and rapidly proliferates.

1. Cell X, a B lymphocyte (B cell) presents a novel peptide on a major histocompatibility complex protein on its surface.
Your Answer:
Answer: C: Activation of immune system cells, cell X initiates cell division and rapidly proliferates. Patrolling CD4+ T cells (Helper T cells) will be activated by the novel peptide and will in turn send a mitogenic signal to the B cell via CD40 ligand:CD40 interactions. Since the most likely reason that a B cell is presenting a novel peptide is that it has picked up a novel protein on its membrane-bound IgM and IgD, the B cell will now be getting two mitogenic signals and will therefore differentiate and proliferate. This process is illustrated in Figure 19.8 on book page 324.
2. Cell X, a body cell (for example, a liver hepatocyte) does not express histocompatibility complex proteins on its surface.
Your Answer:
Answer: A: Activation of immune system cells and triggering of apoptosis in cell X. Patrolling natural killer cells release granzymes and perforin onto any cell that is not expressing histocompatibility complex proteins on its surface. This process is described on book page 323.
3. Cell X, a body cell (for example, a liver hepatocyte) presents a novel peptide on a major histocompatibility complex protein on its surface.
Your Answer:
Answer: A: Activation of immune system cells and triggering of apoptosis in cell X. Patrolling CD8+ T cells (cytotoxic T cells) will detect the novel peptide and kill cell X by presentation of Fas ligand together with the release of granzymes and perforin. This process is illustrated in Figure 19.7 on book page 323.
4. Cell X, a dendritic cell, presents a novel peptide on a major histocompatibility complex protein on its surface.
Your Answer:
Answer: B: Activation of immune system cells, cell X continues its normal role, neither undergoing apoptosis not proliferating. Contact with a dendritic cell presenting a novel peptide causes proliferation in those T cells whose T cell receptor binds strongly to the MHC-peptide complex. This process is illustrated in Figure 19.6 on book page 322.
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