Immunology: T Cells and Adaptive Immunity
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Questions and Answers

What is the purpose of negative selection in T cell development?

  • To eliminate T cells that recognize self-antigens (correct)
  • To stimulate T cells to proliferate
  • To differentiate between CD4 and CD8 T cells
  • To enhance T cell response to pathogens

    • Which T cell co-receptors are involved during positive selection?

  • CD4 and CD8 (correct)
  • CD45 and CD56
  • CD3 and CD28
  • CD40 and CD19

    • What is a characteristic of double positive T cells?

  • They express both CD4 and CD8 co-receptors (correct)
  • They are exclusively CD4 positive
  • They are mature T cells ready for activation
  • They lack T cell receptors

    • During which checkpoint do T cells recognize an MHC molecule?

    <p>Positive selection</p> Signup and view all the answers

    What type of T cell is created when a T cell successfully differentiates through positive selection?

    <p>CD4+ single positive</p> Signup and view all the answers

    How do naïve T cells respond to self-antigens during negative selection?

    <p>They recognize self-antigens only weakly</p> Signup and view all the answers

    What is the outcome of a T cell that successfully recognizes a self-antigen during negative selection?

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

    What role does the lymph node play for naïve T cells?

    <p>Circulation and monitoring for antigens</p> Signup and view all the answers

    What is the primary function of Cytotoxic T cells (CD8+)?

    <p>Kill infected or altered cells</p> Signup and view all the answers

    Which cytokine is produced by Th1 cells?

    <p>IFN-γ</p> Signup and view all the answers

    Which type of pathogen is primarily targeted by Th2 cells?

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

    What immune cells do Th1 cells primarily act upon?

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

    What cytokine is produced by antigen presenting cells (APC) to activate T helper cells?

    <p>IL-12</p> Signup and view all the answers

    What is the first step in T cell development?

    <p>TCR rearrangement</p> Signup and view all the answers

    In which tissue do T cells undergo activation?

    <p>Lymph nodes</p> Signup and view all the answers

    What type of T cell is primarily responsible for killing infected cells?

    <p>CD8+ T cells</p> Signup and view all the answers

    Which function is associated with CD4+ T cells?

    <p>Helping B cells and macrophages</p> Signup and view all the answers

    What does the term 'naïve T cell' refer to?

    <p>A mature T cell that hasn't yet met an antigen</p> Signup and view all the answers

    What is the significance of clonal expansion in T cells?

    <p>It produces numerous antigen-specific T cells</p> Signup and view all the answers

    Which phase occurs after T cell activation?

    <p>Differentiation into effector cells</p> Signup and view all the answers

    What role do checkpoints play in T cell development?

    <p>They ensure the selection of appropriate T cells</p> Signup and view all the answers

    Where are effector T cells primarily active?

    <p>Peripheral tissues</p> Signup and view all the answers

    What do CD8+ T cells differentiate into after activation?

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

    During which process do T cells mature into either CD4+ or CD8+ T cells?

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

    What is a key distinguishing feature of helper T cells?

    <p>They assist other immune cells in response</p> Signup and view all the answers

    What happens to immature T cells in the thymus?

    <p>They undergo selection processes</p> Signup and view all the answers

    What is the role of IL-5 in the immune system?

    <p>Stimulates mast cells and IgE production</p> Signup and view all the answers

    Which interleukin is primarily involved in inducing Th17 responses?

    <p>IL-23</p> Signup and view all the answers

    What is the function of regulatory T cells (Treg) in the immune response?

    <p>Promote production of IL-10 to suppress immune responses</p> Signup and view all the answers

    What is the primary action of cytotoxic T lymphocytes (CTLs)?

    <p>Destroy virally infected cells</p> Signup and view all the answers

    Which of the following is true about the substances released by activated CTLs?

    <p>They contain perforin and granzymes for cell death</p> Signup and view all the answers

    Which T helper cell type is primarily associated with allergies?

    <p>Th2</p> Signup and view all the answers

    What type of antigens do cytotoxic T cells recognize?

    <p>Viral antigens on MHC class I molecules</p> Signup and view all the answers

    What is the relationship between IL-10 and Tregs in immune regulation?

    <p>Tregs release IL-10 to inhibit other T helper responses</p> Signup and view all the answers

    What is the primary function of IL-2 in T cell biology?

    <p>Acts as a growth factor for T cells</p> Signup and view all the answers

    What happens during clonal expansion of T cells?

    <p>Activated T cells proliferate to form a large population</p> Signup and view all the answers

    Where does T cell activation primarily occur?

    <p>Lymph nodes</p> Signup and view all the answers

    What are CD8+ T cells primarily responsible for?

    <p>Cytotoxic activity against infected cells</p> Signup and view all the answers

    Which type of T cell helps in mounting an appropriate immune response?

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

    What is the role of memory T cells?

    <p>To circulate and respond to future infections</p> Signup and view all the answers

    What characterizes T regulatory cells?

    <p>They help maintain immune tolerance</p> Signup and view all the answers

    What occurs in the peripheral tissue regarding effector T cells?

    <p>They enter systemic circulation</p> Signup and view all the answers

    What are the subtypes of T helper cells?

    <p>Th1, Th2, Th17</p> Signup and view all the answers

    What triggers the activation of T cells?

    <p>Interaction with antigen-presenting cells</p> Signup and view all the answers

    What is the role of autocrine signaling via IL-2?

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

    What is a distinguishing feature of resting T lymphocytes?

    <p>Low metabolic activity</p> Signup and view all the answers

    What is the function of CD4+ T helper cells in relation to B cells?

    <p>Stimulate their antibody production</p> Signup and view all the answers

    What happens to T cells during initial antigen exposure?

    <p>They proliferate and differentiate</p> Signup and view all the answers

    What is the first signal required for T cell activation?

    <p>Antigen recognition by TCR</p> Signup and view all the answers

    Which co-receptor interacts with MHC class II molecules during T cell activation?

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

    What role do adhesion molecules like integrin play in T cell activation?

    <p>They stabilize the synapse between T cells and APCs.</p> Signup and view all the answers

    What factors stimulate antigen-presenting cells to express co-stimulatory receptors?

    <p>Presence of microbes</p> Signup and view all the answers

    What must bind to CD28 on T cells for their proper activation?

    <p>B7 co-stimulatory molecules</p> Signup and view all the answers

    Which instructive cytokines stimulate the Th1 subset of CD4+ T cells?

    <p>IL-12 and IFNγ</p> Signup and view all the answers

    Which cytokine is crucial for the development of Th2 cells?

    <p>IL-4</p> Signup and view all the answers

    What is the primary function of CD4+ T cells?

    <p>Supporting other immune cells</p> Signup and view all the answers

    In which type of infections are Th1 cells primarily involved?

    <p>Intracellular bacterial infections</p> Signup and view all the answers

    What is the consequence of not receiving co-stimulation for T cell activation?

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

    What kind of cells act as APCs to present antigens to T cells?

    <p>Dendritic cells and others</p> Signup and view all the answers

    Which process is NOT necessary for the activation of naive T cells?

    <p>Presence of antibodies</p> Signup and view all the answers

    Why do different cytokines direct the differentiation of various CD4+ T cell subsets?

    <p>Each cytokine is specific to a type of pathogen.</p> Signup and view all the answers

    What occurs during the positive selection of T cells in relation to CD4 and CD8?

    <p>T cells become CD4 single positive or CD8 single positive.</p> Signup and view all the answers

    What happens to T cells that bind tightly to self-peptides during negative selection?

    <p>T cells undergo apoptosis.</p> Signup and view all the answers

    At what stage of development does negative selection primarily occur?

    <p>Around 7-8 weeks of gestation.</p> Signup and view all the answers

    Which outcome occurs when a T cell's TCR binds to self-peptide weakly or not at all during negative selection?

    <p>The T cell survives and matures.</p> Signup and view all the answers

    What is the primary role of Cytotoxic T cells (CD8+)?

    <p>Kill infected or altered cells</p> Signup and view all the answers

    Which T helper subset is associated with producing IFN-γ?

    <p>Th1</p> Signup and view all the answers

    Which cytokine is produced by antigen presenting cells to activate T helper cells?

    <p>IL-12</p> Signup and view all the answers

    Which T helper subset primarily targets intracellular pathogens?

    <p>Th1</p> Signup and view all the answers

    What type of cells do Th2 cells primarily act upon?

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

    What cytokine is primarily produced by T helper cells to activate B cells?

    <p>IL-13</p> Signup and view all the answers

    What is a primary function of IL-10 in relation to T regulatory (Treg) cells?

    <p>Suppress Th1, Th2, and Th17 responses</p> Signup and view all the answers

    Which T helper cell type is primarily activated during responses to extracellular bacterial and yeast infections?

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

    What mechanism do cytotoxic T lymphocytes (CTL) primarily use to kill infected cells?

    <p>Perforin and granzymes that induce apoptosis</p> Signup and view all the answers

    What distinguishes cytotoxic T cells from other T cells in terms of their role?

    <p>They directly kill virally infected cells.</p> Signup and view all the answers

    Which of the following is associated with Th2 cell responses?

    <p>Mediating allergic reactions</p> Signup and view all the answers

    What role do antigen presenting cells (APCs) play in T cell activation?

    <p>They display antigens on MHC class I and II molecules.</p> Signup and view all the answers

    What effect does Treg (regulatory T cells) have on the immune response?

    <p>It prevents excessive immune reactions.</p> Signup and view all the answers

    Which subtype of CD4+ T cells is primarily involved in the response to infections?

    <p>Th1</p> Signup and view all the answers

    What is a primary cytokine secreted by Th2 cells?

    <p>IL-5</p> Signup and view all the answers

    Which type of immune cell is predominantly activated by Th2 cells?

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

    What is the role of regulatory T cells (Treg) in the immune system?

    <p>Induce self-tolerance</p> Signup and view all the answers

    What is self-tolerance in relation to T cells?

    <p>T cells remaining unresponsive to self antigens</p> Signup and view all the answers

    Which cytokine is NOT typically associated with Th1 cells?

    <p>IL-4</p> Signup and view all the answers

    Which response best describes the function of IL-5 in the immune system?

    <p>Enhances eosinophil production</p> Signup and view all the answers

    During an immune response, which type of T cell is primarily responsible for modulating allergic reactions?

    <p>Th2</p> Signup and view all the answers

    What are the two main functions of T cells in the adaptive immune system?

    <p>Helping immune responses and killing infected cells</p> Signup and view all the answers

    What do T helper cells primarily help with in the immune response?

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

    Which T helper cell subset is primarily involved in fighting extracellular pathogens?

    <p>Th2</p> Signup and view all the answers

    Where do T cells undergo maturation and selection?

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

    How do T cells recognize antigens?

    <p>Through T cell receptors (TCR) interacting with MHC-peptide complexes</p> Signup and view all the answers

    What are memory T cells responsible for?

    <p>Providing long-term immunity against previously encountered antigens</p> Signup and view all the answers

    What is the consequence of positive selection during T cell development?

    <p>T cells are eliminated if they do not recognize MHC</p> Signup and view all the answers

    What differentiates cytotoxic T cells from T helper cells?

    <p>Cytotoxic T cells primarily kill infected cells, whereas T helper cells assist other immune cells</p> Signup and view all the answers

    What immune mechanism do regulatory T cells (Tregs) primarily utilize?

    <p>Suppressing the activity of other immune cells to maintain tolerance</p> Signup and view all the answers

    What defines T cell activation?

    <p>Recognition of antigen-MHC complexes through TCRs and co-stimulation</p> Signup and view all the answers

    Which of the following statements is true about the diversity of T cell receptors (TCRs)?

    <p>TCR diversity is crucial for effective recognition of various antigens</p> Signup and view all the answers

    What is the primary role of cytokines produced by T helper cells?

    <p>To recruit and activate other immune cells</p> Signup and view all the answers

    Which type of antigen do cytotoxic T cells predominantly target?

    <p>Intracellular pathogens and cancer cells</p> Signup and view all the answers

    What is produced by activated T cells that promotes their own growth?

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

    Into which types of cells do a fraction of activated T cells differentiate after exposure to an antigen?

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

    Where does initial T cell activation occur?

    <p>Lymph nodes</p> Signup and view all the answers

    What distinguishes helper T cells (CD4+) from cytotoxic T cells (CD8+)?

    <p>CD4+ cells assist other immune cells.</p> Signup and view all the answers

    What is the primary role of T regulatory cells (Tregs) in the immune response?

    <p>Maintain immune tolerance and prevent autoimmunity</p> Signup and view all the answers

    Which subset of T helper cells is primarily involved in the response to bacterial and yeast infections?

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

    What triggers the clonal expansion of T cells?

    <p>Antigen-specific activation</p> Signup and view all the answers

    What function do activated T cells perform once they enter systemic circulation?

    <p>Carry out their effector functions</p> Signup and view all the answers

    What type of T cells develop in the thymus?

    <p>Immature T cells.</p> Signup and view all the answers

    What is the role of autocrine signaling via IL-2 in T cell biology?

    <p>It stimulates T cell proliferation.</p> Signup and view all the answers

    During what stage does T cell differentiation occur into either CD4+ or CD8+ T cells?

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

    What characterizes effector T cells?

    <p>They perform their functions in peripheral tissue.</p> Signup and view all the answers

    Which interleukin is primarily associated with inducing T helper cell activation?

    <p>IL-12</p> Signup and view all the answers

    What occurs after clonal expansion of T cells?

    <p>T cells leave the lymphoid tissue.</p> Signup and view all the answers

    What happens to activated T cells during their effector function?

    <p>They interact with other immune cells to fight infections.</p> Signup and view all the answers

    What is the outcome for a T cell if the TCR binds tightly to a self-peptide during negative selection?

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

    At which stage do T cells express both CD4 and CD8 co-receptors?

    <p>When they are double positive</p> Signup and view all the answers

    What happens if a T cell's TCR does not bind self-peptide during negative selection?

    <p>The T cell either dies or goes on to mature</p> Signup and view all the answers

    What primarily dictates whether a T cell survives negative selection?

    <p>The binding affinity of TCR to self-peptides</p> Signup and view all the answers

    During which developmental stage do T cells transition from double positive to single positive?

    <p>Following positive selection in the thymus</p> Signup and view all the answers

    What describes the role of naive T cells in the lymph nodes?

    <p>They circulate in secondary lymph organs.</p> Signup and view all the answers

    Which of the following is NOT required for the activation of naive T cells?

    <p>Migration to the site of infection.</p> Signup and view all the answers

    What process occurs after a naive T cell recognizes an antigen?

    <p>It starts clonal expansion.</p> Signup and view all the answers

    Which statement accurately reflects the diversity of T cells?

    <p>T cells possess a single unique TCR.</p> Signup and view all the answers

    Which molecules play an important role in the activation signals for T cells?

    <p>B7 and CD28.</p> Signup and view all the answers

    What is the final outcome for activated T cells after successfully proliferating?

    <p>They leave the lymph node to engage targets.</p> Signup and view all the answers

    Which aspect of T cell activation is most dependent on antigen presentation?

    <p>Recognition by TCR.</p> Signup and view all the answers

    What defines the diversity of T cell receptors (TCRs) among naive T cells?

    <p>They are each specific to a unique antigen.</p> Signup and view all the answers

    What is the main role of CD4+ T cells in the immune response?

    <p>Provide help to B cells and macrophages</p> Signup and view all the answers

    Which phase follows T cell activation in their life cycle?

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

    What is the primary location for T cell activation to occur?

    <p>Lymph nodes</p> Signup and view all the answers

    Which type of T cells are directly responsible for cytotoxic activity?

    <p>CD8+ T cells</p> Signup and view all the answers

    What occurs in peripheral tissues following T cell activation?

    <p>T cells perform effector functions</p> Signup and view all the answers

    What type of response do CD4+ T cells assist in primarily?

    <p>Adaptive immune response</p> Signup and view all the answers

    How do effector T cells recognize their target antigens?

    <p>Through T cell receptors (TCRs)</p> Signup and view all the answers

    What determines the fate of immature T cells in the thymus?

    <p>Recognition of self-antigens</p> Signup and view all the answers

    What is a key characteristic of memory T cells?

    <p>They provide long-lasting immunity</p> Signup and view all the answers

    What is primarily responsible for the death of effector T cells after an immune response?

    <p>Activation of inhibitory pathways</p> Signup and view all the answers

    What happens to CD4 and CD8 T cell responses when T regulatory cells are activated?

    <p>Responses are inhibited</p> Signup and view all the answers

    Which of the following signals is NOT decreased leading to T cell apoptosis?

    <p>Proinflammatory cytokines</p> Signup and view all the answers

    What is the primary tissue where T cell development occurs?

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

    Which pathway is involved in inhibiting T cell activation signals?

    <p>CTLA-4 and PD-1 pathways</p> Signup and view all the answers

    What is the main function of CD8+ T cells upon activation?

    <p>Killing infected cells</p> Signup and view all the answers

    Where does most T cell activation take place?

    <p>Lymph nodes</p> Signup and view all the answers

    What role does the lymphatic system play in T cell function?

    <p>Facilitates antigen recognition</p> Signup and view all the answers

    Which of the following statements correctly describes CD4+ T cells?

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

    Which cells primarily respond to helminthic infections?

    <p>Th2 cells</p> Signup and view all the answers

    What is a characteristic feature of Severe Combined Immunodeficiency (SCID)?

    <p>Absence of T and B lymphocytes</p> Signup and view all the answers

    Which of the following is a potential outcome for infants with Severe Combined Immunodeficiency (SCID)?

    <p>Typically fatal within the first two years of life</p> Signup and view all the answers

    During which stage do T cells undergo TCR rearrangement?

    <p>In the thymus</p> Signup and view all the answers

    What happens to T cells after activation?

    <p>They undergo differentiation into effector and memory cells.</p> Signup and view all the answers

    Which T cell type plays a crucial role in helping B cells produce antibodies?

    <p>CD4+ T helper cells</p> Signup and view all the answers

    What is the primary function of CD8+ T cells after they become activated?

    <p>To directly kill infected or cancerous cells</p> Signup and view all the answers

    What does differentiation into the CD4/CD8 lineage signify for T cells?

    <p>They are maturing and selecting specific functions.</p> Signup and view all the answers

    What is a common feature of congenital heart problems associated with genetic conditions?

    <p>They often have a familial inheritance pattern.</p> Signup and view all the answers

    Which immune response is typically affected in individuals with hypocalcaemia?

    <p>Compromised ability to mount an effective immune response</p> Signup and view all the answers

    What is the primary role of Thymic selection in T cell development?

    <p>To prevent autoreactive T cells from entering circulation.</p> Signup and view all the answers

    What is the role of TCR during T cell development?

    <p>It is involved in the rearrangement and selection of T cell lineages.</p> Signup and view all the answers

    Which statement accurately describes the migration of immature T cells?

    <p>They migrate from bone marrow to the thymus where they develop.</p> Signup and view all the answers

    What phase occurs after the activation of naïve T cells?

    <p>Clonal expansion and differentiation into effector cells.</p> Signup and view all the answers

    Which feature distinguishes CD4+ T cells from CD8+ T cells?

    <p>CD4+ T cells provide help to B cells and macrophages.</p> Signup and view all the answers

    During which process are T cells exposed to antigens for the first time?

    <p>Antigen exposure within the lymph nodes.</p> Signup and view all the answers

    What is the primary consequence of T cell checkpoints during development?

    <p>They ensure only appropriate T cells survive.</p> Signup and view all the answers

    What is a key function of CD8+ T cells in the immune response?

    <p>They directly kill virus-infected or damaged cells.</p> Signup and view all the answers

    What distinguishes differentiated CD4+ T cells from naïve T cells?

    <p>Differentiated CD4+ T cells have undergone selection processes.</p> Signup and view all the answers

    Which of the following best describes the fate of T cells after activation?

    <p>They differentiate into memory T cells for future responses.</p> Signup and view all the answers

    What initiates the T cell activation process?

    <p>Antigen presentation by antigen-presenting cells.</p> Signup and view all the answers

    What is the significance of T cell effector functions in response to pathogens?

    <p>They facilitate direct killing or help in the immune response.</p> Signup and view all the answers

    Where do T cells primarily exert their effector functions?

    <p>In peripheral tissues following activation.</p> Signup and view all the answers

    What occurs during the clonal expansion of T cells after activation?

    <p>A single activated T cell produces multiple identical daughter cells.</p> Signup and view all the answers

    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) aid immune responses.
      • Cytotoxic T cells (CTL) kill cells infected by intracellular pathogens (and cancerous cells).

    Immunology Lectures Outline

    • Barrier Immunity: Physical, Mechanical, and Chemical barriers provide immediate defense.
    • Innate Immunity: Cytokines, inflammation, complement, and antigen presentation, offering defense in minutes to hours.
    • Adaptive Immunity: Response to extracellular and intracellular infections. T helper cells (help B cells, cytotoxic tcells, and other immune cells) and B cells (antibodies).

    Lecture Learning Outcomes

    • Understand the roles of T cells and their development, including receptor rearrangement.
    • Learn about the positive and negative selection processes for T cell development.
    • Define and describe T cell activation and Effector functions of T helper cells/ cytotoxic T cells.
    • Distinguish between various helper T cell subsets (Th1, Th2, Th17, Treg) and their roles in infections.
    • Describe central and peripheral tolerance for T cells.

    Key Roles of T Cells

    • T cells are part of the adaptive immune system, responding to specific antigens.
    • Two key functions:
      • Helper T cells help activate other immune cells.
      • Cytotoxic T cells directly kill infected cells.

    Antigen Presentation

    • MHC class II and MHC class I molecules display peptide antigens on the cell surface.
    • MHC-peptide complexes are recognized by T cells, triggering immune responses.
    • MHC class II interacts with T helper cells, MHC class I with cytotoxic T cells.

    Unique Features of T Cells

    • T cells function by interacting with other cells, mainly antigen-presenting cells (APCs).
    • Each T cell has a unique T cell receptor (TCR) for antigen recognition, leading to a diverse array of responses.
    • T cell activation triggers clonal expansion and differentiation into effector cells or memory cells. Memory T cells live for more than 20 years.

    Pertinent Questions

    • Origins of T cells.
    • Mechanisms of TCR expression with specific affinity for peptides.
    • The importance of T cell activation and its process.
    • Distinguishing features of T helper and cytotoxic T cells.

    Life Cycle of a T Cell

    • T cell development occurs in the thymus.
    • T cells are activated in secondary lymphoid tissues, such as lymph nodes.
    • Activated T cells differentiate into effector cells to perform their specific functions (Helper or Cytotoxic).
    • The effector cells carry out their functions in peripheral tissues.

    T Cell Development

    • T cells originate from bone marrow precursors.
    • They travel to the thymus where they mature—developing essential features, like the TCR and CD4/CD8 markers. 98% of immature T cells die without meeting the requirements.
    • The final population of functional T cells has vast diversity.

    Checkpoints

    • Ensure T cells express the necessary T cell receptors (TCR), can recognize MHCs, and can avoid reacting against self-antigens.
    • At each checkpoint, the vast majority of immature thymocytes die/ fail.

    T cell Receptor (TCR)

    • Millions of T cells have a unique single TCR.
    • It's a membrane protein with a variable region for antigen binding and a constant region.
    • The variable region makes each TCR antigen-specific.

    Creating T Cells

    • The DNA level of TCR genes undergoes rearrangement uniquely for every T cell, generating a vast diversity of TCR responses.
    • The VDJ recombination process in T cell development combines V(D)J gene segments to create diverse TCRs. 10^14 different unique receptors are possible.

    Positive Selection

    • The interaction of T cells with MHC molecules in the thymus, which ensures T cells recognize MHC molecules.
    • T cells that do not recognize self-MHC molecules in the thymus die.
    • Successful cells get a positive signal and continue development.

    Negative Selection

    • Recognition of self-peptides/antigens, triggering apoptosis (programmed cell death).
    • This process eliminates T cells that would potentially attack the body's own tissues, preventing autoimmunity,
    • Cells that bind to self-antigens in a 'moderate' or 'weak' capacity live on while those that have very strong binding die.

    T cell Activation

    • Naive T cells encounter antigens presented by antigen-presenting cells (APCs).
    • The interaction of the T cell receptor with the processed antigens causes the cell to proliferate and differentiate (clonal expansion).
    • T-cells then leave the secondary lymphoid tissue to produce effector functions.

    Signal 1

    • Antigen presentation.
    • The T cell receptor binds to the antigen presented on the MHC molecules, which triggers the first signal for activation.
    • Antigens from pathogens cause signaling.

    Signal 2

    • Co-stimulation.
    • The second signal for T cell activation comes from co-stimulatory molecules, such as CD28, on T cells interacting with B7 on antigen-presenting cells, This helps ensure T cells only respond to "real" antigens.
    • Microbes stimulate APCs to express B7 molecules.
    • CD28 and B7 interactions are crucial for full T cell activation

    Signal 3

    • Instructive cytokines.
    • Cytokines, from APCs, direct T cell differentiation into various subtypes (e.g., Th1, Th2, Th17).
    • Signals 1, 2, and 3 together correctly determine the responses needed against microbes.
    • Without these interactions, the T cell will not function properly, especially when in the presence of a pathogen.

    T Cell Subsets

    • Helper T cells (CD4+ T cells) orchestrate the adaptive immune response through cytokine production. Diverse helper T cells with various functions:
      • Th1: intracellular bacterial infections.
      • Th2: helminth infections
      • Th17: extracellular bacterial and fungal infections
    • Cytotoxic T cells- (CD8+ T cells) directly kill infected cells.

    Clonal Expansion

    • Activated T cells rapidly produce IL-2, a potent growth factor.
    • Extensive clonal expansion of the activated T-cell occurs, creating a large and effective population to combat the pathogen.

    T Cell Effector Function

    • Activated T cells leave their original site of activation and circulate systemically to carry out their roles.

    T Cell Homeostasis

    • Once the pathogen has been cleared, the effector T cells often die, resulting in homeostasis or maintenance of the immune system’s balance.
    • Inhibitory signals like CTLA-4 and PD-1 stop further T cell activation. T regulatory cells (Treg) control inflammation.

    T Cell Immunodeficiencies

    • Defects in T-cell development or function cause serious immunodeficiency diseases like SCID.
    • Problems like DiGeorge syndrome show deletions that affect t cells and cause recurrent infections and other health issues.

    Autoimmunity

    • Failure of tolerance mechanisms causes auto-reactive T cells, leading to autoimmunity.
    • T cells attack healthy body tissues, resulting in autoimmune disorders.

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    Adaptive Immunity - T Cells PDF 2024 (RCSI)

    Description

    Explore the intricate roles of T cells within the adaptive immune system. This quiz covers T cell functions, development, and their response to pathogens, emphasizing helper and cytotoxic T cells. Test your understanding of key immunological concepts and T cell activation processes.

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