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Questions and Answers
What is the initial site of T cell formation before they mature?
Which type of selection ensures that T cells do not recognize self antigens?
What determines whether a T cell develops into a CD4 or CD8 cell?
In which structure are Hassall's corpuscles found?
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Which cells can be converted into T regulatory cells?
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Where are T cells initially produced?
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Which of the following describes the role of the thymus gland?
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What happens to the thymus gland as a person ages?
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What is the primary function of chemotactic agents secreted by the thymus gland?
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Which of the following is NOT a chemotactic agent associated with the thymus gland?
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At what stage of life is the thymus gland most functional?
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What occurs to T cell precursors before they enter the thymus gland?
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Which anatomical structures does the thymus gland overlie?
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What is the relationship between T cells and B cells in the bone marrow?
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Which process do T cells undergo in the thymus gland?
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What is NOT characteristic of the thymus gland during early adolescence?
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Which additional factor aids in drawing T cell precursors to the thymus gland?
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What term describes the movement of T cell precursors towards the thymus gland?
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What happens to a T cell if it fails to recognize MHC class I or II molecules?
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What is the role of the chemical 'F' mentioned in the selection process of T cells?
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Which of the following statements accurately describes negative selection in T cell maturation?
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What must happen for a T cell to be considered functionally mature?
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What is the consequence of a TCR binding perfectly to a self peptide?
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Which CD molecules are expressed by a T cell that is undergoing both positive and negative selection?
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How does a T cell know to downregulate CD8 upon interaction with MHC class II?
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What triggers apoptosis in T cells failing to recognize foreign antigens during positive selection?
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What kind of interaction is essential for the proper maturation of T cells?
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Which event is indicative of successful positive selection in T cells?
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What determines the fate of a T cell during the selection process?
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Which statement is true regarding the selection of T cells in the thymus?
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What does undergoing apoptosis during T cell selection indicate about a T cell?
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What primary function does the thymus gland perform in relation to T cells?
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Which protein is crucial for shuffling T cell DNA during T cell development?
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What is the significance of CD4 and CD8 proteins on T cells?
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What do the terms MHC1 and MHC2 refer to?
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What occurs if a T cell fails to recognize MHC molecules appropriately?
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What role do thymic epithelial cells play in T cell development?
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Which aspect of T cell receptors is influenced by rag genes during T cell development?
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Why is positive selection important in the development of T cells?
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What is the primary function of rag proteins in T cell maturation?
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What marks the success of a T cell during the selection process in the thymus?
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Which types of antigens can TCRs recognize due to the activities of rag proteins?
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What is the initial result of T cell interaction with thymic epithelial cells secreting thymic factors?
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In the context of T cells, what does the term 'apoptosis' refer to?
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What is the main purpose of cluster differentiation (CD) proteins in T cells?
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What is the primary function of CD4 molecules on T helper cells?
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What type of cell is produced when a T helper cell downregulates CD4 and upregulates CD8?
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Which cytokine is mentioned as influential in the differentiation into T regulatory cells?
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What happens to CD8 molecules when a T cell interacts with MHC class I?
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Where do T regulatory cells primarily concentrate within the immune system?
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What is the significance of TCR molecules on T cells?
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Which statement best describes the transformation of T helper or cytotoxic cells into T regulatory cells?
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What structure do T cells surround in the spleen to form white pulp?
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Which cell type is typically downregulated in T helper cells upon interaction with MHC class I?
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What distinguishes T regulatory cells from other T cells?
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Which characteristic is primarily associated with cytotoxic T cells?
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What is the outcome for T helper cells when they receive a strong signal from antigen presentation?
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How do T cells access lymph nodes after differentiation?
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Which T cell subset is primarily associated with promoting inflammation?
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What is a notable characteristic of MHC-II compared to MHC-I?
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Which interaction is essential for T cell recruitment to sites of infection?
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Which of the following statements is true regarding cytotoxic T cells?
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What specifically facilitates the binding of peptides to MHC molecules?
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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.
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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.
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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.
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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
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TH1 cells release:
- Interferon gamma (IFN-γ)
- Tumor necrosis factor alpha (TNF-α)
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TH2 cells release:
- Interleukin 4 (IL-4)
- Interleukin 5 (IL-5)
- Interleukin 13 (IL-13)
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TH17 cells release:
- Interleukin 17 (IL-17)
- Interleukin 22 (IL-22)
- Tumor necrosis factor alpha (TNF-α)
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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
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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
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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.
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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
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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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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.
