Podcast
Questions and Answers
What is the purpose of negative selection in T cell development?
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?
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?
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?
During which checkpoint do T cells recognize an MHC molecule?
What type of T cell is created when a T cell successfully differentiates through positive selection?
What type of T cell is created when a T cell successfully differentiates through positive selection?
How do naïve T cells respond to self-antigens during negative selection?
How do naïve T cells respond to self-antigens during negative selection?
What is the outcome of a T cell that successfully recognizes a self-antigen during negative selection?
What is the outcome of a T cell that successfully recognizes a self-antigen during negative selection?
What role does the lymph node play for naïve T cells?
What role does the lymph node play for naïve T cells?
What is the primary function of Cytotoxic T cells (CD8+)?
What is the primary function of Cytotoxic T cells (CD8+)?
Which cytokine is produced by Th1 cells?
Which cytokine is produced by Th1 cells?
Which type of pathogen is primarily targeted by Th2 cells?
Which type of pathogen is primarily targeted by Th2 cells?
What immune cells do Th1 cells primarily act upon?
What immune cells do Th1 cells primarily act upon?
What cytokine is produced by antigen presenting cells (APC) to activate T helper cells?
What cytokine is produced by antigen presenting cells (APC) to activate T helper cells?
What is the first step in T cell development?
What is the first step in T cell development?
In which tissue do T cells undergo activation?
In which tissue do T cells undergo activation?
What type of T cell is primarily responsible for killing infected cells?
What type of T cell is primarily responsible for killing infected cells?
Which function is associated with CD4+ T cells?
Which function is associated with CD4+ T cells?
What does the term 'naïve T cell' refer to?
What does the term 'naïve T cell' refer to?
What is the significance of clonal expansion in T cells?
What is the significance of clonal expansion in T cells?
Which phase occurs after T cell activation?
Which phase occurs after T cell activation?
What role do checkpoints play in T cell development?
What role do checkpoints play in T cell development?
Where are effector T cells primarily active?
Where are effector T cells primarily active?
What do CD8+ T cells differentiate into after activation?
What do CD8+ T cells differentiate into after activation?
During which process do T cells mature into either CD4+ or CD8+ T cells?
During which process do T cells mature into either CD4+ or CD8+ T cells?
What is a key distinguishing feature of helper T cells?
What is a key distinguishing feature of helper T cells?
What happens to immature T cells in the thymus?
What happens to immature T cells in the thymus?
What is the role of IL-5 in the immune system?
What is the role of IL-5 in the immune system?
Which interleukin is primarily involved in inducing Th17 responses?
Which interleukin is primarily involved in inducing Th17 responses?
What is the function of regulatory T cells (Treg) in the immune response?
What is the function of regulatory T cells (Treg) in the immune response?
What is the primary action of cytotoxic T lymphocytes (CTLs)?
What is the primary action of cytotoxic T lymphocytes (CTLs)?
Which of the following is true about the substances released by activated CTLs?
Which of the following is true about the substances released by activated CTLs?
Which T helper cell type is primarily associated with allergies?
Which T helper cell type is primarily associated with allergies?
What type of antigens do cytotoxic T cells recognize?
What type of antigens do cytotoxic T cells recognize?
What is the relationship between IL-10 and Tregs in immune regulation?
What is the relationship between IL-10 and Tregs in immune regulation?
What is the primary function of IL-2 in T cell biology?
What is the primary function of IL-2 in T cell biology?
What happens during clonal expansion of T cells?
What happens during clonal expansion of T cells?
Where does T cell activation primarily occur?
Where does T cell activation primarily occur?
What are CD8+ T cells primarily responsible for?
What are CD8+ T cells primarily responsible for?
Which type of T cell helps in mounting an appropriate immune response?
Which type of T cell helps in mounting an appropriate immune response?
What is the role of memory T cells?
What is the role of memory T cells?
What characterizes T regulatory cells?
What characterizes T regulatory cells?
What occurs in the peripheral tissue regarding effector T cells?
What occurs in the peripheral tissue regarding effector T cells?
What are the subtypes of T helper cells?
What are the subtypes of T helper cells?
What triggers the activation of T cells?
What triggers the activation of T cells?
What is the role of autocrine signaling via IL-2?
What is the role of autocrine signaling via IL-2?
What is a distinguishing feature of resting T lymphocytes?
What is a distinguishing feature of resting T lymphocytes?
What is the function of CD4+ T helper cells in relation to B cells?
What is the function of CD4+ T helper cells in relation to B cells?
What happens to T cells during initial antigen exposure?
What happens to T cells during initial antigen exposure?
What is the first signal required for T cell activation?
What is the first signal required for T cell activation?
Which co-receptor interacts with MHC class II molecules during T cell activation?
Which co-receptor interacts with MHC class II molecules during T cell activation?
What role do adhesion molecules like integrin play in T cell activation?
What role do adhesion molecules like integrin play in T cell activation?
What factors stimulate antigen-presenting cells to express co-stimulatory receptors?
What factors stimulate antigen-presenting cells to express co-stimulatory receptors?
What must bind to CD28 on T cells for their proper activation?
What must bind to CD28 on T cells for their proper activation?
Which instructive cytokines stimulate the Th1 subset of CD4+ T cells?
Which instructive cytokines stimulate the Th1 subset of CD4+ T cells?
Which cytokine is crucial for the development of Th2 cells?
Which cytokine is crucial for the development of Th2 cells?
What is the primary function of CD4+ T cells?
What is the primary function of CD4+ T cells?
In which type of infections are Th1 cells primarily involved?
In which type of infections are Th1 cells primarily involved?
What is the consequence of not receiving co-stimulation for T cell activation?
What is the consequence of not receiving co-stimulation for T cell activation?
What kind of cells act as APCs to present antigens to T cells?
What kind of cells act as APCs to present antigens to T cells?
Which process is NOT necessary for the activation of naive T cells?
Which process is NOT necessary for the activation of naive T cells?
Why do different cytokines direct the differentiation of various CD4+ T cell subsets?
Why do different cytokines direct the differentiation of various CD4+ T cell subsets?
What occurs during the positive selection of T cells in relation to CD4 and CD8?
What occurs during the positive selection of T cells in relation to CD4 and CD8?
What happens to T cells that bind tightly to self-peptides during negative selection?
What happens to T cells that bind tightly to self-peptides during negative selection?
At what stage of development does negative selection primarily occur?
At what stage of development does negative selection primarily occur?
Which outcome occurs when a T cell's TCR binds to self-peptide weakly or not at all during negative selection?
Which outcome occurs when a T cell's TCR binds to self-peptide weakly or not at all during negative selection?
What is the primary role of Cytotoxic T cells (CD8+)?
What is the primary role of Cytotoxic T cells (CD8+)?
Which T helper subset is associated with producing IFN-γ?
Which T helper subset is associated with producing IFN-γ?
Which cytokine is produced by antigen presenting cells to activate T helper cells?
Which cytokine is produced by antigen presenting cells to activate T helper cells?
Which T helper subset primarily targets intracellular pathogens?
Which T helper subset primarily targets intracellular pathogens?
What type of cells do Th2 cells primarily act upon?
What type of cells do Th2 cells primarily act upon?
What cytokine is primarily produced by T helper cells to activate B cells?
What cytokine is primarily produced by T helper cells to activate B cells?
What is a primary function of IL-10 in relation to T regulatory (Treg) cells?
What is a primary function of IL-10 in relation to T regulatory (Treg) cells?
Which T helper cell type is primarily activated during responses to extracellular bacterial and yeast infections?
Which T helper cell type is primarily activated during responses to extracellular bacterial and yeast infections?
What mechanism do cytotoxic T lymphocytes (CTL) primarily use to kill infected cells?
What mechanism do cytotoxic T lymphocytes (CTL) primarily use to kill infected cells?
What distinguishes cytotoxic T cells from other T cells in terms of their role?
What distinguishes cytotoxic T cells from other T cells in terms of their role?
Which of the following is associated with Th2 cell responses?
Which of the following is associated with Th2 cell responses?
What role do antigen presenting cells (APCs) play in T cell activation?
What role do antigen presenting cells (APCs) play in T cell activation?
What effect does Treg (regulatory T cells) have on the immune response?
What effect does Treg (regulatory T cells) have on the immune response?
Which subtype of CD4+ T cells is primarily involved in the response to infections?
Which subtype of CD4+ T cells is primarily involved in the response to infections?
What is a primary cytokine secreted by Th2 cells?
What is a primary cytokine secreted by Th2 cells?
Which type of immune cell is predominantly activated by Th2 cells?
Which type of immune cell is predominantly activated by Th2 cells?
What is the role of regulatory T cells (Treg) in the immune system?
What is the role of regulatory T cells (Treg) in the immune system?
What is self-tolerance in relation to T cells?
What is self-tolerance in relation to T cells?
Which cytokine is NOT typically associated with Th1 cells?
Which cytokine is NOT typically associated with Th1 cells?
Which response best describes the function of IL-5 in the immune system?
Which response best describes the function of IL-5 in the immune system?
During an immune response, which type of T cell is primarily responsible for modulating allergic reactions?
During an immune response, which type of T cell is primarily responsible for modulating allergic reactions?
What are the two main functions of T cells in the adaptive immune system?
What are the two main functions of T cells in the adaptive immune system?
What do T helper cells primarily help with in the immune response?
What do T helper cells primarily help with in the immune response?
Which T helper cell subset is primarily involved in fighting extracellular pathogens?
Which T helper cell subset is primarily involved in fighting extracellular pathogens?
Where do T cells undergo maturation and selection?
Where do T cells undergo maturation and selection?
How do T cells recognize antigens?
How do T cells recognize antigens?
What are memory T cells responsible for?
What are memory T cells responsible for?
What is the consequence of positive selection during T cell development?
What is the consequence of positive selection during T cell development?
What differentiates cytotoxic T cells from T helper cells?
What differentiates cytotoxic T cells from T helper cells?
What immune mechanism do regulatory T cells (Tregs) primarily utilize?
What immune mechanism do regulatory T cells (Tregs) primarily utilize?
What defines T cell activation?
What defines T cell activation?
Which of the following statements is true about the diversity of T cell receptors (TCRs)?
Which of the following statements is true about the diversity of T cell receptors (TCRs)?
What is the primary role of cytokines produced by T helper cells?
What is the primary role of cytokines produced by T helper cells?
Which type of antigen do cytotoxic T cells predominantly target?
Which type of antigen do cytotoxic T cells predominantly target?
What is produced by activated T cells that promotes their own growth?
What is produced by activated T cells that promotes their own growth?
Into which types of cells do a fraction of activated T cells differentiate after exposure to an antigen?
Into which types of cells do a fraction of activated T cells differentiate after exposure to an antigen?
Where does initial T cell activation occur?
Where does initial T cell activation occur?
What distinguishes helper T cells (CD4+) from cytotoxic T cells (CD8+)?
What distinguishes helper T cells (CD4+) from cytotoxic T cells (CD8+)?
What is the primary role of T regulatory cells (Tregs) in the immune response?
What is the primary role of T regulatory cells (Tregs) in the immune response?
Which subset of T helper cells is primarily involved in the response to bacterial and yeast infections?
Which subset of T helper cells is primarily involved in the response to bacterial and yeast infections?
What triggers the clonal expansion of T cells?
What triggers the clonal expansion of T cells?
What function do activated T cells perform once they enter systemic circulation?
What function do activated T cells perform once they enter systemic circulation?
What type of T cells develop in the thymus?
What type of T cells develop in the thymus?
What is the role of autocrine signaling via IL-2 in T cell biology?
What is the role of autocrine signaling via IL-2 in T cell biology?
During what stage does T cell differentiation occur into either CD4+ or CD8+ T cells?
During what stage does T cell differentiation occur into either CD4+ or CD8+ T cells?
What characterizes effector T cells?
What characterizes effector T cells?
Which interleukin is primarily associated with inducing T helper cell activation?
Which interleukin is primarily associated with inducing T helper cell activation?
What occurs after clonal expansion of T cells?
What occurs after clonal expansion of T cells?
What happens to activated T cells during their effector function?
What happens to activated T cells during their effector function?
What is the outcome for a T cell if the TCR binds tightly to a self-peptide during negative selection?
What is the outcome for a T cell if the TCR binds tightly to a self-peptide during negative selection?
At which stage do T cells express both CD4 and CD8 co-receptors?
At which stage do T cells express both CD4 and CD8 co-receptors?
What happens if a T cell's TCR does not bind self-peptide during negative selection?
What happens if a T cell's TCR does not bind self-peptide during negative selection?
What primarily dictates whether a T cell survives negative selection?
What primarily dictates whether a T cell survives negative selection?
During which developmental stage do T cells transition from double positive to single positive?
During which developmental stage do T cells transition from double positive to single positive?
What describes the role of naive T cells in the lymph nodes?
What describes the role of naive T cells in the lymph nodes?
Which of the following is NOT required for the activation of naive T cells?
Which of the following is NOT required for the activation of naive T cells?
What process occurs after a naive T cell recognizes an antigen?
What process occurs after a naive T cell recognizes an antigen?
Which statement accurately reflects the diversity of T cells?
Which statement accurately reflects the diversity of T cells?
Which molecules play an important role in the activation signals for T cells?
Which molecules play an important role in the activation signals for T cells?
What is the final outcome for activated T cells after successfully proliferating?
What is the final outcome for activated T cells after successfully proliferating?
Which aspect of T cell activation is most dependent on antigen presentation?
Which aspect of T cell activation is most dependent on antigen presentation?
What defines the diversity of T cell receptors (TCRs) among naive T cells?
What defines the diversity of T cell receptors (TCRs) among naive T cells?
What is the main role of CD4+ T cells in the immune response?
What is the main role of CD4+ T cells in the immune response?
Which phase follows T cell activation in their life cycle?
Which phase follows T cell activation in their life cycle?
What is the primary location for T cell activation to occur?
What is the primary location for T cell activation to occur?
Which type of T cells are directly responsible for cytotoxic activity?
Which type of T cells are directly responsible for cytotoxic activity?
What occurs in peripheral tissues following T cell activation?
What occurs in peripheral tissues following T cell activation?
What type of response do CD4+ T cells assist in primarily?
What type of response do CD4+ T cells assist in primarily?
How do effector T cells recognize their target antigens?
How do effector T cells recognize their target antigens?
What determines the fate of immature T cells in the thymus?
What determines the fate of immature T cells in the thymus?
What is a key characteristic of memory T cells?
What is a key characteristic of memory T cells?
What is primarily responsible for the death of effector T cells after an immune response?
What is primarily responsible for the death of effector T cells after an immune response?
What happens to CD4 and CD8 T cell responses when T regulatory cells are activated?
What happens to CD4 and CD8 T cell responses when T regulatory cells are activated?
Which of the following signals is NOT decreased leading to T cell apoptosis?
Which of the following signals is NOT decreased leading to T cell apoptosis?
What is the primary tissue where T cell development occurs?
What is the primary tissue where T cell development occurs?
Which pathway is involved in inhibiting T cell activation signals?
Which pathway is involved in inhibiting T cell activation signals?
What is the main function of CD8+ T cells upon activation?
What is the main function of CD8+ T cells upon activation?
Where does most T cell activation take place?
Where does most T cell activation take place?
What role does the lymphatic system play in T cell function?
What role does the lymphatic system play in T cell function?
Which of the following statements correctly describes CD4+ T cells?
Which of the following statements correctly describes CD4+ T cells?
Which cells primarily respond to helminthic infections?
Which cells primarily respond to helminthic infections?
What is a characteristic feature of Severe Combined Immunodeficiency (SCID)?
What is a characteristic feature of Severe Combined Immunodeficiency (SCID)?
Which of the following is a potential outcome for infants with Severe Combined Immunodeficiency (SCID)?
Which of the following is a potential outcome for infants with Severe Combined Immunodeficiency (SCID)?
During which stage do T cells undergo TCR rearrangement?
During which stage do T cells undergo TCR rearrangement?
What happens to T cells after activation?
What happens to T cells after activation?
Which T cell type plays a crucial role in helping B cells produce antibodies?
Which T cell type plays a crucial role in helping B cells produce antibodies?
What is the primary function of CD8+ T cells after they become activated?
What is the primary function of CD8+ T cells after they become activated?
What does differentiation into the CD4/CD8 lineage signify for T cells?
What does differentiation into the CD4/CD8 lineage signify for T cells?
What is a common feature of congenital heart problems associated with genetic conditions?
What is a common feature of congenital heart problems associated with genetic conditions?
Which immune response is typically affected in individuals with hypocalcaemia?
Which immune response is typically affected in individuals with hypocalcaemia?
What is the primary role of Thymic selection in T cell development?
What is the primary role of Thymic selection in T cell development?
What is the role of TCR during T cell development?
What is the role of TCR during T cell development?
Which statement accurately describes the migration of immature T cells?
Which statement accurately describes the migration of immature T cells?
What phase occurs after the activation of naïve T cells?
What phase occurs after the activation of naïve T cells?
Which feature distinguishes CD4+ T cells from CD8+ T cells?
Which feature distinguishes CD4+ T cells from CD8+ T cells?
During which process are T cells exposed to antigens for the first time?
During which process are T cells exposed to antigens for the first time?
What is the primary consequence of T cell checkpoints during development?
What is the primary consequence of T cell checkpoints during development?
What is a key function of CD8+ T cells in the immune response?
What is a key function of CD8+ T cells in the immune response?
What distinguishes differentiated CD4+ T cells from naïve T cells?
What distinguishes differentiated CD4+ T cells from naïve T cells?
Which of the following best describes the fate of T cells after activation?
Which of the following best describes the fate of T cells after activation?
What initiates the T cell activation process?
What initiates the T cell activation process?
What is the significance of T cell effector functions in response to pathogens?
What is the significance of T cell effector functions in response to pathogens?
Where do T cells primarily exert their effector functions?
Where do T cells primarily exert their effector functions?
What occurs during the clonal expansion of T cells after activation?
What occurs during the clonal expansion of T cells after activation?
Flashcards
T cell development checkpoints
T cell development checkpoints
Steps in T cell maturation to ensure appropriate T cells are selected.
Double positive T cells
Double positive T cells
T cells expressing both CD4 and CD8 co-receptors.
Single positive T cells
Single positive T cells
T cells expressing either CD4 or CD8, but not both.
Positive selection
Positive selection
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Negative selection
Negative selection
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MHC Molecules
MHC Molecules
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Naïve T cells
Naïve T cells
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Autoimmunity
Autoimmunity
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T Cell Development
T Cell Development
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CD4+ T Cells
CD4+ T Cells
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CD8+ T Cells
CD8+ T Cells
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T Cell Activation
T Cell Activation
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Effector T Cells
Effector T Cells
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Antigen Exposure
Antigen Exposure
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Thymus
Thymus
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Selection Process
Selection Process
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Clonal Expansion
Clonal Expansion
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TCR (T Cell Receptor)
TCR (T Cell Receptor)
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T Helper Cells
T Helper Cells
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Cytotoxic T Cells
Cytotoxic T Cells
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Peripheral Tissue
Peripheral Tissue
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Lymph Nodes
Lymph Nodes
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Signal 1 (T cell activation)
Signal 1 (T cell activation)
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Signal 2 (T cell activation)
Signal 2 (T cell activation)
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Signal 3 (T cell activation)
Signal 3 (T cell activation)
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Antigen
Antigen
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MHC II molecule
MHC II molecule
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CD4 co-receptor
CD4 co-receptor
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APC (Antigen-Presenting Cell)
APC (Antigen-Presenting Cell)
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CD28
CD28
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Th1 cells
Th1 cells
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Th2 cells
Th2 cells
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Cytokines
Cytokines
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IL-12
IL-12
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IL-4
IL-4
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MHC Class I
MHC Class I
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T helper 1 (Th1)
T helper 1 (Th1)
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T helper 2 (Th2)
T helper 2 (Th2)
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What activates T helper cells?
What activates T helper cells?
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What do T helper cells do?
What do T helper cells do?
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What is clonal expansion?
What is clonal expansion?
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What do memory T cells do?
What do memory T cells do?
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T cell effector function
T cell effector function
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What is the role of IL-2 in T cell activation?
What is the role of IL-2 in T cell activation?
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T regulatory cells
T regulatory cells
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How do T cells carry out their effector function?
How do T cells carry out their effector function?
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What is the role of IL-23 in T cell activation?
What is the role of IL-23 in T cell activation?
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What is the difference between resting and activated T lymphocytes?
What is the difference between resting and activated T lymphocytes?
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CTL (Cytotoxic T Lymphocyte)
CTL (Cytotoxic T Lymphocyte)
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Perforin
Perforin
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Granzymes
Granzymes
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Apoptosis
Apoptosis
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TCR
TCR
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How do T helper cells differentiate?
How do T helper cells differentiate?
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Memory T Cells
Memory T Cells
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CD4+ T Cells (Helper T cells)
CD4+ T Cells (Helper T cells)
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CD8+ T Cells (Cytotoxic T cells)
CD8+ T Cells (Cytotoxic T cells)
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Antigen-Presenting Cells (APCs)
Antigen-Presenting Cells (APCs)
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Co-stimulation
Co-stimulation
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T Helper Cells (Th)
T Helper Cells (Th)
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Cytotoxic T Lymphocytes (CTL)
Cytotoxic T Lymphocytes (CTL)
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Adaptive Immunity
Adaptive Immunity
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Helper T cells (Th)
Helper T cells (Th)
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Cytotoxic T cells (CTL)
Cytotoxic T cells (CTL)
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T Cell Receptor (TCR)
T Cell Receptor (TCR)
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Antigen Presentation
Antigen Presentation
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T Cell Memory
T Cell Memory
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What activates Th1 cells?
What activates Th1 cells?
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What activates Th2 cells?
What activates Th2 cells?
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What do Th1 cells do?
What do Th1 cells do?
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What do Th2 cells do?
What do Th2 cells do?
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Self-Tolerance
Self-Tolerance
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MHC (Major Histocompatibility Complex)
MHC (Major Histocompatibility Complex)
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What are Naïve T cells?
What are Naïve T cells?
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Where does T cell activation occur?
Where does T cell activation occur?
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Signals for T cell activation
Signals for T cell activation
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What is CD28?
What is CD28?
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What are MHC II molecules?
What are MHC II molecules?
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What are cytokines?
What are cytokines?
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What are the major consequences of SCID?
What are the major consequences of SCID?
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What are the key characteristics of a T cell?
What are the key characteristics of a T cell?
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What is the thymus?
What is the thymus?
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What happens during positive selection?
What happens during positive selection?
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What happens during negative selection?
What happens during negative selection?
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What is T cell activation?
What is T cell activation?
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What are the main types of T cell effector functions?
What are the main types of T cell effector functions?
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What is the role of cytokines in T cell activation?
What is the role of cytokines in T cell activation?
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T Cell Homeostasis
T Cell Homeostasis
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T Cell Activation: Signal 1
T Cell Activation: Signal 1
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T Cell Activation: Signal 2
T Cell Activation: Signal 2
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T Cell Activation: Signal 3
T Cell Activation: Signal 3
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CD4+ Helper T Cells (Th)
CD4+ Helper T Cells (Th)
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CD8+ Cytotoxic T Cells (CTL)
CD8+ Cytotoxic T Cells (CTL)
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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) 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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