The Immune System's Defense Against Cytosolic Pathogens
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Questions and Answers

Which type of microbes are relatively resistant to the microbicidal mechanisms of phagocytes?

  • Microbes that directly enter the cytosol
  • Microbes that are confined to vesicles
  • Microbes that escape from phagosomes into the cytosol (correct)
  • Microbes that are ingested by phagocytes

What is the effector mechanism of T cell-mediated immunity that is required to eradicate cytosolic pathogens?

  • Natural killer cells
  • B cells
  • CD8+ CTLs (correct)
  • CD4+ helper T cells

What is the basis for the designation of CD8+ T lymphocytes as cytotoxic?

  • Their ability to kill infected cells expressing the antigen
  • Their synthesis of molecules involved in cell killing (correct)
  • Their differentiation into fully active CTLs
  • Their ability to recognize class I MHC-associated peptides

Which cytokine is responsible for activation of macrophages in infections and in disease states where excessive activation of CD8+ T cells may be a feature?

<p>Interferon-gamma (IFN-γ) (D)</p> Signup and view all the answers

Which type of T lymphocytes may function cooperatively to destroy intracellular microbes?

<p>Both CD4+ and CD8+ T cells (A)</p> Signup and view all the answers

What is the mechanism by which CD8+ cytotoxic T lymphocytes (CTLs) kill infected cells?

<p>Inducing apoptosis of the target cell (A)</p> Signup and view all the answers

Which type of cells can capture antigens of infected cells and tumors and present them on class I MHC molecules?

<p>Dendritic cells (D)</p> Signup and view all the answers

What is required for the differentiation of naive CD8+ T cells into functional CTLs and memory cells?

<p>Costimulation and help from CD4+ T cells (D)</p> Signup and view all the answers

Which molecules on the surface of infected cells do CD8+ CTLs recognize?

<p>Class I MHC–peptide complexes (B)</p> Signup and view all the answers

What is the main mechanism by which CTLs kill target cells?

<p>Delivery of granzymes into the cytosol (A)</p> Signup and view all the answers

Flashcards

Microbes that escape from phagosomes

These pathogens are difficult for phagocytes to destroy because they can escape the phagosome and enter the cytoplasm of the cell.

CD8+ CTLs

CD8+ cytotoxic T lymphocytes (CTLs) are a type of T cell that directly kills infected cells by inducing apoptosis.

What makes CD8+ T cells cytotoxic?

CD8+ T lymphocytes are cytotoxic because they produce and release molecules like granzyme and perforin, which directly kill infected cells.

What activates macrophages and can enhance CD8+ T cell activity?

Interferon-gamma (IFN-γ) is a powerful cytokine that activates macrophages and can also lead to enhanced CD8+ T cell activity.

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Types of T cells that work together against intracellular microbes

Both CD4+ helper T cells and CD8+ cytotoxic T cells can work together to eliminate intracellular microbes.

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How do CD8+ CTLs kill infected cells?

CD8+ CTLs kill infected cells by delivering cytotoxic molecules like granzyme and perforin, which trigger programmed cell death (apoptosis).

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Cells capturing antigens and presenting them on class I MHC

Dendritic cells act like scouts, capturing pieces of infected cells and tumors. They present these antigens on class I MHC molecules to CD8+ T cells to trigger an immune response.

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What's required for CD8+ T cell differentiation?

Naive CD8+ T cells need additional signals, including costimulation from other immune cells and help from CD4+ T cells, to become fully functional CTLs and memory cells.

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What do CD8+ CTLs recognize on infected cells?

CD8+ CTLs recognize specific antigen fragments presented on class I MHC molecules by infected cells. This recognition triggers the killing process.

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Main mechanism of CTL mediated killing

CTLs predominantly kill target cells by delivering granzyme, a molecule that enters the cytosol and triggers apoptosis.

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