Cell Mediated Immunity and Antigen Recognition - 2.2
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Questions and Answers

What is the initial site of T cell formation before they mature?

  • Red bone marrow (correct)
  • Spleen
  • Thymus
  • Lymph nodes

    • Which type of selection ensures that T cells do not recognize self antigens?

  • Negative selection (correct)
  • Positive selection
  • Adaptive selection
  • Random selection

    • What determines whether a T cell develops into a CD4 or CD8 cell?

  • Interaction with MHC molecules (correct)
  • Location of maturation
  • Presence of IL-2
  • Type of antigen present

    • In which structure are Hassall's corpuscles found?

    <p>Thymus gland</p> Signup and view all the answers

    Which cells can be converted into T regulatory cells?

    <p>T helper cells and T cytotoxic cells</p> Signup and view all the answers

    Where are T cells initially produced?

    <p>Red bone marrow</p> Signup and view all the answers

    Which of the following describes the role of the thymus gland?

    <p>It is the primary organ for T cell maturation.</p> Signup and view all the answers

    What happens to the thymus gland as a person ages?

    <p>It atrophies and becomes filled with fibrous tissue.</p> Signup and view all the answers

    What is the primary function of chemotactic agents secreted by the thymus gland?

    <p>To attract T cell precursors to the thymus gland.</p> Signup and view all the answers

    Which of the following is NOT a chemotactic agent associated with the thymus gland?

    <p>Interferon</p> Signup and view all the answers

    At what stage of life is the thymus gland most functional?

    <p>Infancy and childhood</p> Signup and view all the answers

    What occurs to T cell precursors before they enter the thymus gland?

    <p>They are not functional and must mature in the thymus.</p> Signup and view all the answers

    Which anatomical structures does the thymus gland overlie?

    <p>Heart and esophagus</p> Signup and view all the answers

    What is the relationship between T cells and B cells in the bone marrow?

    <p>Both arise from the same progenitor cell type.</p> Signup and view all the answers

    Which process do T cells undergo in the thymus gland?

    <p>Maturation and clonal expansion</p> Signup and view all the answers

    What is NOT characteristic of the thymus gland during early adolescence?

    <p>Activates T cell production</p> Signup and view all the answers

    Which additional factor aids in drawing T cell precursors to the thymus gland?

    <p>Thymic factors</p> Signup and view all the answers

    What term describes the movement of T cell precursors towards the thymus gland?

    <p>Chemotaxis</p> Signup and view all the answers

    What happens to a T cell if it fails to recognize MHC class I or II molecules?

    <p>It undergoes apoptosis.</p> Signup and view all the answers

    What is the role of the chemical 'F' mentioned in the selection process of T cells?

    <p>To bind to receptors on T cells and trigger apoptosis.</p> Signup and view all the answers

    Which of the following statements accurately describes negative selection in T cell maturation?

    <p>It eliminates T cells that have strong affinity for self-antigens.</p> Signup and view all the answers

    What must happen for a T cell to be considered functionally mature?

    <p>It must engage with MHC class II and downregulate CD8 molecules.</p> Signup and view all the answers

    What is the consequence of a TCR binding perfectly to a self peptide?

    <p>The T cell will undergo apoptosis.</p> Signup and view all the answers

    Which CD molecules are expressed by a T cell that is undergoing both positive and negative selection?

    <p>CD4 and CD8</p> Signup and view all the answers

    How does a T cell know to downregulate CD8 upon interaction with MHC class II?

    <p>Through signaling pathways initiated by CD4 binding.</p> Signup and view all the answers

    What triggers apoptosis in T cells failing to recognize foreign antigens during positive selection?

    <p>Lack of interaction with foreign peptides.</p> Signup and view all the answers

    What kind of interaction is essential for the proper maturation of T cells?

    <p>Binding of TCRs to MHC molecules presenting antigens.</p> Signup and view all the answers

    Which event is indicative of successful positive selection in T cells?

    <p>Binding to MHC class II molecules.</p> Signup and view all the answers

    What determines the fate of a T cell during the selection process?

    <p>The affinity of its TCR for self-peptide.</p> Signup and view all the answers

    Which statement is true regarding the selection of T cells in the thymus?

    <p>T cells undergo apoptosis if they do not bind to MHC molecules.</p> Signup and view all the answers

    What does undergoing apoptosis during T cell selection indicate about a T cell?

    <p>It has a strong affinity for self-antigens.</p> Signup and view all the answers

    What primary function does the thymus gland perform in relation to T cells?

    <p>It shuffles T cell DNA to create diverse receptors</p> Signup and view all the answers

    Which protein is crucial for shuffling T cell DNA during T cell development?

    <p>Recombinase-activating gene (rag)</p> Signup and view all the answers

    What is the significance of CD4 and CD8 proteins on T cells?

    <p>They enhance the binding to MHC molecules</p> Signup and view all the answers

    What do the terms MHC1 and MHC2 refer to?

    <p>Types of major histocompatibility complex molecules</p> Signup and view all the answers

    What occurs if a T cell fails to recognize MHC molecules appropriately?

    <p>It undergoes apoptosis</p> Signup and view all the answers

    What role do thymic epithelial cells play in T cell development?

    <p>They secrete chemokines that activate T cell genes</p> Signup and view all the answers

    Which aspect of T cell receptors is influenced by rag genes during T cell development?

    <p>The diversity of antigens they can recognize</p> Signup and view all the answers

    Why is positive selection important in the development of T cells?

    <p>It ensures T cells can effectively recognize foreign antigens</p> Signup and view all the answers

    What is the primary function of rag proteins in T cell maturation?

    <p>They facilitate DNA shuffling for receptor diversity</p> Signup and view all the answers

    What marks the success of a T cell during the selection process in the thymus?

    <p>The T cell binds weakly to MHC molecules</p> Signup and view all the answers

    Which types of antigens can TCRs recognize due to the activities of rag proteins?

    <p>Any shape of foreign antigen</p> Signup and view all the answers

    What is the initial result of T cell interaction with thymic epithelial cells secreting thymic factors?

    <p>Activation of DNA shuffling genes</p> Signup and view all the answers

    In the context of T cells, what does the term 'apoptosis' refer to?

    <p>Normal programmed cell death</p> Signup and view all the answers

    What is the main purpose of cluster differentiation (CD) proteins in T cells?

    <p>To serve as markers for different T cell types</p> Signup and view all the answers

    What is the primary function of CD4 molecules on T helper cells?

    <p>To assist in the activation of other immune cells</p> Signup and view all the answers

    What type of cell is produced when a T helper cell downregulates CD4 and upregulates CD8?

    <p>Cytotoxic T cell</p> Signup and view all the answers

    Which cytokine is mentioned as influential in the differentiation into T regulatory cells?

    <p>Interleukin-2</p> Signup and view all the answers

    What happens to CD8 molecules when a T cell interacts with MHC class I?

    <p>They are downregulated</p> Signup and view all the answers

    Where do T regulatory cells primarily concentrate within the immune system?

    <p>Thymus gland</p> Signup and view all the answers

    What is the significance of TCR molecules on T cells?

    <p>They interact with MHC molecules to recognize antigens</p> Signup and view all the answers

    Which statement best describes the transformation of T helper or cytotoxic cells into T regulatory cells?

    <p>They can retain some TCRs but will show CD4 or CD8 as needed</p> Signup and view all the answers

    What structure do T cells surround in the spleen to form white pulp?

    <p>Blood vessels</p> Signup and view all the answers

    Which cell type is typically downregulated in T helper cells upon interaction with MHC class I?

    <p>CD4</p> Signup and view all the answers

    What distinguishes T regulatory cells from other T cells?

    <p>Ability to suppress immune responses</p> Signup and view all the answers

    Which characteristic is primarily associated with cytotoxic T cells?

    <p>Destruction of virus-infected cells</p> Signup and view all the answers

    What is the outcome for T helper cells when they receive a strong signal from antigen presentation?

    <p>They proliferate and activate other cells</p> Signup and view all the answers

    How do T cells access lymph nodes after differentiation?

    <p>By migrating through lymphatic vessels</p> Signup and view all the answers

    Which T cell subset is primarily associated with promoting inflammation?

    <p>Th17</p> Signup and view all the answers

    What is a notable characteristic of MHC-II compared to MHC-I?

    <p>MHC-II activates helper T cells.</p> Signup and view all the answers

    Which interaction is essential for T cell recruitment to sites of infection?

    <p>CXCR3 + CXCL10 chemokine</p> Signup and view all the answers

    Which of the following statements is true regarding cytotoxic T cells?

    <p>They use serine esterases, like granzymes, to kill infected cells.</p> Signup and view all the answers

    What specifically facilitates the binding of peptides to MHC molecules?

    <p>The shape of the antigen binding groove allows peptide ends to protrude.</p> Signup and view all the answers

    Study Notes

    T-Cell Development

    • T-cells are produced in the red bone marrow.
    • T-cells mature in the thymus gland.
    • The thymus gland is a primary lymphoid organ, located in the mediastinum and overlies the heart.
    • The thymus gland is most active during early childhood and adolescence.
    • The thymus gland secretes chemicals including thymosin, thymopoietin, and thymic factors which attract T-cells to the thymus.
    • T-cells undergo maturation in the thymus gland.
    • T-cells express proteins called TCRs (T cell receptors) and CD proteins (cluster differentiation proteins).
    • TCRs are produced by recombination enzymes RAG1 and RAG2 which shuffle DNA to produce different receptors to recognize various antigens.
    • T-cells express either CD4 or CD8, they do not express both.
    • The thymus gland expresses MHC1 and MHC2 molecules which interact with CD proteins on T-cells.
    • MHC molecules have self peptides that bind to TCRs.
    • T-cells undergo a process called positive selection, where they are selected to interact with MHC molecules. T-cells that do not recognize MHC molecules appropriately undergo apoptosis.
    • T-cells undergo a process called negative selection, where they are selected not to interact with self peptides. T-cells that recognize self peptides undergo apoptosis.
    • T-cells that interact with MHC2 molecules will down regulate CD8 proteins, becoming T helper cells.
    • T-cells that interact with MHC1 molecules will down regulate CD4 proteins, becoming T cytotoxic cells.

    T Helper Cells

    • T helper cells express a high number of CD4 proteins.
    • T helper cells interact with MHC2 molecules.
    • T helper cells do not express CD8 proteins.

    T Cytotoxic Cells

    • T cytotoxic cells express a high number of CD8 proteins.
    • T cytotoxic cells interact with MHC1 molecules.
    • T cytotoxic cells do not express CD4 proteins.

    T Cell Maturation Summary

    • The thymus gland plays a vital role in the selection and maturation of T-cells.
    • Through a series of interactions and processes, immature T-cells are selected to become either T helper cells or T cytotoxic cells.
    • This ensures that T-cells are able to recognize foreign antigens while avoiding self-reactivity.

    T Cell Development

    • T cells mature in the thymus: T cells are produced in the red bone marrow but mature in the thymus.
    • Positive selection: T cells undergo positive selection in the thymus, recognizing MHC molecules. Cells that fail to recognize MHC molecules die.
    • Negative selection: T cells further undergo negative selection to eliminate self-reactive cells. Cells that bind to self-antigens die.
    • CD4 versus CD8: T lymphocytes differentiate into CD4+ or CD8+ cells based on which MHC molecule they recognize.
      • CD4+ cells: Recognize MHC class II molecules expressed on antigen-presenting cells, leading to their differentiation into helper T cells.
      • CD8+ cells: Recognize MHC class I molecules expressed on all nucleated cells. These cells become cytotoxic T cells.
    • T regulatory cells: Some CD4+ and CD8+ cells can differentiate into T regulatory cells (Treg cells).
      • Characteristics: These cells can express both CD4, TCRs, and CD8 molecules.
      • Function: Treg cells play a vital role in immune suppression, preventing autoimmune reactions.
      • Mechanism: The exact mechanisms for differentiation into Treg cells are complex, but they involve proteins like CD25 and cytokines like interleukin-2.
    • Lymph Node Localization: Mature naive T cells migrate to secondary lymphoid organs like lymph nodes.
      • Lymph Node Location: These cells are found in the deep part of the cortex.
    • Spleen Localization: T cells can also be found in the spleen, specifically in the white pulp around capillaries, forming periarteriolar lymphatic sheaths.
    • Thymus Localization: Mature T cells, particularly Treg cells, can be found in the thymus gland, specifically in Hassal's corpuscles.

    Summary

    • This process summarizes how T cells develop and differentiate into various subtypes within the immune system.
    • From their initial production in the red bone marrow to their maturation in the thymus and subsequent migration to secondary lymphoid organs, T cells play crucial roles in immune responses.

    T Cell Development

    • Stem cells differentiate into T cell precursors in the bone marrow.
    • Precursors migrate to the thymus and undergo several stages of development.
    • T cells differentiate into either CD8+ or CD4+ T cells based on the expression of specific receptors.
    • CD8+ T cells become cytotoxic T cells (CTLs)
    • CD4+ T cells become helper T cells (TH)
    • TH cells differentiate further into subsets:
      • TH1 cells promote inflammation and cell-mediated immunity
      • TH2 cells reduce inflammation and promote humoral immunity
      • TH17 cells promote inflammation and are linked to periodontal disease
      • Treg cells reduce inflammation

    TH Cell Subset Functions and Cytokine Release

    • TH1 cells release:
      • Interferon gamma (IFN-γ)
      • Tumor necrosis factor alpha (TNF-α)
    • TH2 cells release:
      • Interleukin 4 (IL-4)
      • Interleukin 5 (IL-5)
      • Interleukin 13 (IL-13)
    • TH17 cells release:
      • Interleukin 17 (IL-17)
      • Interleukin 22 (IL-22)
      • Tumor necrosis factor alpha (TNF-α)
    • Treg cells release:
      • Interleukin 10 (IL-10)
      • Transforming growth factor beta (TGF-β)

    MHC (Major Histocompatibility Complex)

    • MHC-I presents antigens to cytotoxic T cells (CTLs) on all nucleated cells.
    • MHC-II presents antigens to helper T cells (TH cells) only on antigen-presenting cells (APCs) including macrophages, dendritic cells, and B cells
    • MHC-I and CTL interactions lead to cell-mediated immunity.
    • MHC-II and TH cell interactions activate humoral immunity.

    MHC-I and CTL Interactions in Cell-Mediated Immunity:

    • MHC-I molecules bind shorter peptides.
    • CTLs recognize and bind to MHC-I-peptide complexes.
    • TCR on the CTL recognizes and binds to the MHC-I / peptide complex.
    • Co-stimulatory signals are delivered between the CTL and MHC-I expressing cell
    • The CTL releases cytotoxic molecules, including granzyme and perforin.
    • Perforin forms pores in the target cell membrane.
    • Granzyme enters the target cell and triggers apoptosis (programmed cell death).
    • The target cell is destroyed.

    MHC-II and TH Cell Interactions in Humoral Immunity:

    • MHC-II molecules bind longer peptides.
    • MHC-II presents antigens to CD4+ T cells (helper T cells).
    • Helper T cells become activated and produce cytokines that stimulate B cells to produce antibodies.
    • Antibodies help neutralize pathogens, activate complement, and enhance phagocytosis.

    Induction Phase of Cell-Mediated Immunity

    • Antigen presenting cells (APCs) capture and process antigens.
    • APCs display processed antigens on MHC-II molecules.
    • APCs migrate to lymph nodes.
    • Naive T cells in the lymph nodes encounter the MHC-II / antigen complex.
    • The T cell receptor (TCR) on naive T cells binds to the MHC-II / antigen complex, activating the T cell.
    • Activation requires co-stimulatory signals from the APC.
    • Activated T cells differentiate and proliferate, forming effector T cells.

    T-Cell Recruitment To Sites of Infection

    • T-cell receptors and their ligands:
      • CD28 on T cells interacts with B7 on macrophages and other APCs, providing a co-stimulatory signal.
      • CD8 on CTLs binds MHC-I.
      • CD4 on helper T cells binds MHC-II
      • LFA-1 on T cells binds ICAM-1 on high endothelial venules (HEVs) for adhesion.
      • VLA-4 on T cells binds VCAM on HEVs for adhesion.
      • CXCR3 on T cells binds CXCL10 chemokine, guiding T cells to sites of inflammation.
      • E/P selectin ligand on T cells binds E/P selectin on HEVs to facilitate rolling.

    Effector Phase of Cell-Mediated Immunity

    • T-cell responses to extracellular microbes:

      • Helper T cells (TH cells) activate macrophages and B cells to produce antibodies.
      • TH1 cells release cytokines that promote inflammation and activate cytotoxic T cells.
      • TH2 cells release cytokines that promote humoral immunity and reduce inflammation.

    • T-cell Responses to Intracellular microbes:

      • Infected macrophages or cells display viral antigens on MHC-I.
      • CTLs recognize the MHC-I / viral antigen complex and kill the infected cells.

    CTL-mediated Lysis of Target Cells

    • T cell killing of infected cells:
      • CTLs bind to the infected target cells via MHC-I / antigen complex.
      • CTLs release cytotoxic granules containing perforin and granzymes and other factors.
      • Perforin forms pores in the target cell membrane.
      • Granzymes enter the target cell and trigger apoptosis (programmed cell death).
      • Cytoplasmic bridge forms between the CTL and infected cell.
      • The infected cell is destroyed.
      • Granzyme release is triggered by calcium signaling.

    Other Key Points

    • Cytokine release from various types of T cells affects a variety of processes associated with immunity, including inflammation and cell differentiation.
    • The induction and effector phases of cell-mediated immunity are tightly regulated to prevent excessive inflammation and autoimmune responses.
    • Cell-mediated immunity plays a crucial role in protecting the body from intracellular pathogens, especially viruses.

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    Cell Mediated Immunity And Antigen Recognition - 2.2 PDF

    Description

    Test your knowledge of T-cell development, including the roles of the thymus gland and the maturation processes of T-cells. This quiz covers key concepts such as TCRs, CD proteins, and the importance of MHC molecules. Perfect for students studying immunology or related fields.

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