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Questions and Answers
T cells develop in the lymph nodes.
T cells develop in the lymph nodes.
False
CD8+ T cells are also known as Helper T cells.
CD8+ T cells are also known as Helper T cells.
False
T cells can have effector functions in peripheral tissue.
T cells can have effector functions in peripheral tissue.
True
T cell activation occurs after antigen exposure.
T cell activation occurs after antigen exposure.
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Immature T cells help respond to recognized antigens.
Immature T cells help respond to recognized antigens.
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CD4+ T cells help B cells and macrophages.
CD4+ T cells help B cells and macrophages.
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The thymus is considered a secondary lymphoid tissue.
The thymus is considered a secondary lymphoid tissue.
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Antibody production is part of T cell effector function.
Antibody production is part of T cell effector function.
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All T cells respond prior to antigen exposure.
All T cells respond prior to antigen exposure.
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Cytotoxic T cells are essential for killing infected cells.
Cytotoxic T cells are essential for killing infected cells.
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Cytotoxic T cells are also known as killer T cells.
Cytotoxic T cells are also known as killer T cells.
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T helper cells activate macrophages primarily through the cytokine IL-12.
T helper cells activate macrophages primarily through the cytokine IL-12.
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Th2 cells produce IL-4, which targets eosinophils.
Th2 cells produce IL-4, which targets eosinophils.
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CD8+ T cells target primarily extracellular pathogens.
CD8+ T cells target primarily extracellular pathogens.
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The cytokine IFN-γ is produced by Th2 cells.
The cytokine IFN-γ is produced by Th2 cells.
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Immature T cells migrate from the lymph nodes to the thymus.
Immature T cells migrate from the lymph nodes to the thymus.
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Naïve T cells have already met an antigen.
Naïve T cells have already met an antigen.
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CD4+ T cells are known as cytotoxic T cells.
CD4+ T cells are known as cytotoxic T cells.
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T cell development occurs in the thymus.
T cell development occurs in the thymus.
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The activation of T cells is unimportant for their function.
The activation of T cells is unimportant for their function.
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T cell checkpoints are necessary for selecting appropriate T cells.
T cell checkpoints are necessary for selecting appropriate T cells.
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Cytotoxic T cells directly kill infected cells.
Cytotoxic T cells directly kill infected cells.
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The clonal expansion of T cells occurs after the initial antigen exposure.
The clonal expansion of T cells occurs after the initial antigen exposure.
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Helper T cells provide help to B cells and macrophages.
Helper T cells provide help to B cells and macrophages.
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T cells can differentiate only into CD4+ cells.
T cells can differentiate only into CD4+ cells.
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T cell activation occurs in the thymus.
T cell activation occurs in the thymus.
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The effector function of T cells occurs in peripheral tissue.
The effector function of T cells occurs in peripheral tissue.
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Naïve T cells can immediately produce antibodies.
Naïve T cells can immediately produce antibodies.
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TCR rearrangement happens during T cell activation.
TCR rearrangement happens during T cell activation.
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Activated T cells rapidly produce IL-2, a T cell growth factor.
Activated T cells rapidly produce IL-2, a T cell growth factor.
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Memory T cells circulate for only a few weeks after activation.
Memory T cells circulate for only a few weeks after activation.
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Th17 cells are associated with responses to bacterial and yeast infections.
Th17 cells are associated with responses to bacterial and yeast infections.
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T cell activation occurs in peripheral tissues.
T cell activation occurs in peripheral tissues.
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Effector T cells carry out their functions in systemic circulation.
Effector T cells carry out their functions in systemic circulation.
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T cells require interaction with other cells to perform their effector functions.
T cells require interaction with other cells to perform their effector functions.
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The initial antigen exposure occurs in the thymus.
The initial antigen exposure occurs in the thymus.
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T regulatory cells are one of the subsets of Helper T cells.
T regulatory cells are one of the subsets of Helper T cells.
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Clonal expansion of T cells occurs after their activation.
Clonal expansion of T cells occurs after their activation.
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Th1 cells and Th2 cells have distinct contributions to the immune response.
Th1 cells and Th2 cells have distinct contributions to the immune response.
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Antigen-specific activated T cells cannot reproduce themselves.
Antigen-specific activated T cells cannot reproduce themselves.
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Resting T lymphocytes are in a state of complete inactivity.
Resting T lymphocytes are in a state of complete inactivity.
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Memory T cells are created after the immune response to an antigen.
Memory T cells are created after the immune response to an antigen.
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Antigen is the necessary first signal for activation of T cells.
Antigen is the necessary first signal for activation of T cells.
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The TCR recognizes a peptide presented on MHC I molecule.
The TCR recognizes a peptide presented on MHC I molecule.
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CD4 co-receptor interacts with residues on the MHC class II.
CD4 co-receptor interacts with residues on the MHC class II.
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Integrins on T cells stabilize the synapse by binding to ligands on B cells.
Integrins on T cells stabilize the synapse by binding to ligands on B cells.
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Naïve T cells can proliferate and differentiate without co-stimulation.
Naïve T cells can proliferate and differentiate without co-stimulation.
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Microbes stimulate APCs to express co-stimulatory receptors.
Microbes stimulate APCs to express co-stimulatory receptors.
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CD28 is a surface receptor on T cells that engages with the B7 molecule.
CD28 is a surface receptor on T cells that engages with the B7 molecule.
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Without CD28 engagement, T cells are fully activated.
Without CD28 engagement, T cells are fully activated.
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Instructive cytokines assist in the differentiation of certain CD4+ T cell subsets.
Instructive cytokines assist in the differentiation of certain CD4+ T cell subsets.
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IL-12 and IFNγ stimulate the Th2 subset of CD4+ T cells.
IL-12 and IFNγ stimulate the Th2 subset of CD4+ T cells.
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Th1 cells are primarily involved in combating bacterial infections.
Th1 cells are primarily involved in combating bacterial infections.
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Th2 cells are associated with helminth infections.
Th2 cells are associated with helminth infections.
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Instructive cytokines are only produced by T cells.
Instructive cytokines are only produced by T cells.
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Cytokines can direct different CD4+ T cell subsets.
Cytokines can direct different CD4+ T cell subsets.
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Cytotoxic T lymphocytes (CTL) kill cells that are infected by pathogens.
Cytotoxic T lymphocytes (CTL) kill cells that are infected by pathogens.
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Activated cytotoxic T cells release perforin to form pores in the pathogen's cell membrane.
Activated cytotoxic T cells release perforin to form pores in the pathogen's cell membrane.
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IL-10 produced by regulatory T cells helps to switch off Th1, Th2, and Th17 responses.
IL-10 produced by regulatory T cells helps to switch off Th1, Th2, and Th17 responses.
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Th17 cells are primarily associated with allergic responses.
Th17 cells are primarily associated with allergic responses.
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All T helper cells help in activating B cells to produce antibodies.
All T helper cells help in activating B cells to produce antibodies.
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Neutrophils are primarily involved in combating viral infections.
Neutrophils are primarily involved in combating viral infections.
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Granzymes released by CTLs can induce apoptosis in infected cells.
Granzymes released by CTLs can induce apoptosis in infected cells.
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MHC class I molecules display antigens from extracellular sources.
MHC class I molecules display antigens from extracellular sources.
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Study Notes
Adaptive Immunity - T Cells
- T cells are part of the adaptive immune system, specifically targeting antigens.
- They have two key functions: -Helper T cells (Th) assist immune responses. -Cytotoxic T cells (CTL) destroy infected and cancerous cells.
Immunology Lectures Outline
- Barrier Immunity: Physical, mechanical, and chemical barriers provide instant protection against infection.
- Innate Immunity: Cytokines, inflammation, complement proteins, and antigen presentation provide protection over minutes to weeks.
- Adaptive Immunity: T cells (cytotoxic and helper) respond to extracellular and intracellular infections. B cells produce antibodies.
Lecture Learning Outcomes
- Students should be able to: -Define the roles of T cells. -Describe T cell development, including receptor rearrangement. -Explain processes for T cell positive and negative selection. -Describe T cell activation. -Define T helper cell and cytotoxic T cell functions. -Identify T helper cell subsets (Th1, Th2, Th17, Treg) and their roles in infection. -Outline T cell tolerance mechanisms (central and peripheral). -List diseases due to T cell defects.
Key Roles of T Cells
- T cells are part of the adaptive immune system.
- T cells have two main functions: -Helper T cells (Th) assist with immune responses. -Cytotoxic T cells (CTL) directly kill infected or cancerous cells.
Antigen Presentation
- MHC class II and MHC class I receptors present antigens on cell surfaces.
- Only peptide antigens are presented, not whole pathogens.
- TCR recognizes the MHC-peptide complex.
- Communication about the pathogen occurs to activate the adaptive immune system.
- MHC class II - T helper cells
- MHC class I - Cytotoxic T cells
Unique Features of T Cells
- T cells interact with other cells to function.
- TCR recognizes antigen bound to MHC.
- Each T cell has a unique TCR.
- T cells undergo clonal expansion after activation.
- T helper and cytotoxic cells have different effector functions.
- T cells create memory cells that persist for many years.
Pertinent Questions
- Where do T cells originate?
- How do T cells express TCR with antigen-specific affinity?
- What is the T cell activation process, and why is it important?
- What are the differences between T helper and cytotoxic T cells?
T Cell Development
- Immature T cells migrate to the thymus from the bone marrow.
- In the thymus, T cells undergo development.
- Mature T cells exit the thymus and circulate as naïve cells (CD4+ or CD8+).
T Cell Checkpoints
- T cells must have a TCR.
- TCRs must recognize MHC.
- TCRs must not recognize self antigens.
T Cell Receptor (TCR)
- TCRs are membrane-bound proteins.
- TCRs are composed of an alpha and a beta chain.
- Each chain has a variable (V) region and a constant (C) region.
- The variable regions differ for each T cell clone and bind specific antigens.
How do we create T cells?
- During T cell development, V(D)J recombination randomly combines variable segments, creating a diverse repertoire of TCRs that can respond to virtually any antigen.
Life Cycle of a T Cell
- T cell development within the thymus.
- T cell activation within secondary lymphoid tissue (like lymph nodes).
- T cell effector function in peripheral tissues.
T Cell Activation (detailed)
- Naïve T cells circulate in lymph nodes.
- TCR recognizes an antigen presented by an antigen-presenting cell (APC).
- Co-stimulation signals (e.g., B7 on APC and CD28 on T cell).
- Instructive cytokines (e.g., IL-2, IL-12) shape T cell development.
- Activation leads to clonal expansion and differentiation into effector cells.
T cell effector function
- Effector T cells leave the lymph nodes and migrate to sites of infection.
- They eliminate infected cells by direct killing and immune responses.
Signals for T Cell Activation
- Signal 1: Antigen recognition. TCR on T cell binds to MHC-peptide complex.
- Signal 2: Co-stimulation. Interaction between co-stimulatory molecules (e.g., CD28 and B7.)
- Signal 3: Cytokines. Cytokine signals help shape T cell differentiation into specific subsets (Th1, Th2, etc.).
T Helper Subsets
- Different kinds of helper cells play distinct roles in immune responses: -Th1: Intracellular infections -Th2: Helminth infections -Th17: Extracellular bacterial/fungal infections
T cell Activation (further summary)
- Naïve T cells circulate in lymph nodes.
- Activation occurs when TCR recognizes antigen presented by an APC.
- Co-stimulation (signal 2) is critical for activation.
- Differentiation into specific T effector cells occurs with specific cytokines (signal 3).
- Effector T cells leave lymph nodes to carry out their functions.
Clonal Expansion
- Activated T cells rapidly increase in number (clonal expansion) producing many effector cells to fight a specific antigen.
Homeostasis
- As antigen is cleared, the majority of effector T cells die by apoptosis.
- Inhibitory pathways are activated and T regulatory cells can dampen responses.
T Cell Immunodeficiencies
- DiGeorge Syndrome: deletion on chromosome 22 affects thymus development resulting in poor T cell production.
- SCID: a diverse group of disorders caused by mutations impacting T and B cells.
Summary of T Cell Maturation
- TCR rearrangement
- Selection process in the thymus
- Differentiation into specific CD4/CD8 lineages
Summary of T Cell Activation
- T cells are activated in lymph nodes.
- Activation depends on antigen recognition, co-stimulation, and cytokine signals
Summary of T Cell Effector Function
- Effector T cells carry out functions in specific tissues.
- T helpers assist other cells and produce cytokines to direct immune responses.
- Cytotoxic T cells directly kill infected cells.
Autoimmunity and Immune Tolerance
- Self-tolerance: T cell unresponsiveness to self-antigen.
- Central tolerance: eliminates autoreactive T cells in the thymus.
- Peripheral tolerance: eliminates autoreactive T cells in peripheral tissues.
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Description
This quiz explores the role of T cells in the adaptive immune system, focusing on their functions as helper and cytotoxic cells. Understand T cell development, activation processes, and the distinctions between T helper and cytotoxic T cells. Students will gain insights into barrier immunity and innate immunity as foundational concepts.
