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Questions and Answers
What is the primary function of dendritic cells in T cell activation?
What is the primary function of dendritic cells in T cell activation?
- To kill infected cells directly
- To remain dormant until activated by T cells
- To present protein antigens to T cells (correct)
- To produce cytokines for T cell proliferation
Which signal is essential for the activation of T cells after antigen recognition?
Which signal is essential for the activation of T cells after antigen recognition?
- Antigen extraction process
- Costimulatory signal (correct)
- Signal from cytokines only
- MHC molecule activation
How do CD40L:CD40 interactions enhance T cell responses?
How do CD40L:CD40 interactions enhance T cell responses?
- By enhancing the activation of antigen-presenting cells (correct)
- By inducing apoptosis in T cells
- By suppressing T cell proliferation
- By promoting viral replication in T cells
What is the consequence of CTLA-4:B7 interactions during T cell activation?
What is the consequence of CTLA-4:B7 interactions during T cell activation?
What role does PD-1 play in T cell regulation?
What role does PD-1 play in T cell regulation?
Which of the following therapies targets the CD40L:CD40 pathway in clinical trials?
Which of the following therapies targets the CD40L:CD40 pathway in clinical trials?
What is the mechanism by which therapeutic costimulatory blockade aims to regulate T cell activity?
What is the mechanism by which therapeutic costimulatory blockade aims to regulate T cell activity?
What is the primary role of IL-2 in T cell responses?
What is the primary role of IL-2 in T cell responses?
Which molecule is primarily expressed on T cells after activation?
Which molecule is primarily expressed on T cells after activation?
What is clonal expansion in the context of T cells?
What is clonal expansion in the context of T cells?
Which factor is essential for the differentiation and function of regulatory T cells?
Which factor is essential for the differentiation and function of regulatory T cells?
How does IL-2 influence the activity of other T cells?
How does IL-2 influence the activity of other T cells?
Which of the following is NOT a change in surface molecule expression following T cell activation?
Which of the following is NOT a change in surface molecule expression following T cell activation?
Which surface molecule is typically associated with the costimulatory signal necessary for T cell activation?
Which surface molecule is typically associated with the costimulatory signal necessary for T cell activation?
What is the main source of IL-2 secretion in the early phase of T cell activation?
What is the main source of IL-2 secretion in the early phase of T cell activation?
What role do adhesion molecules play in T cell activation?
What role do adhesion molecules play in T cell activation?
What characterizes the increased expression of anti-apoptotic proteins in memory T cells?
What characterizes the increased expression of anti-apoptotic proteins in memory T cells?
How do memory T cells respond to antigen stimulation compared to naive T cells?
How do memory T cells respond to antigen stimulation compared to naive T cells?
What is the role of cytokines like IL-7 in memory T cell maintenance?
What is the role of cytokines like IL-7 in memory T cell maintenance?
What triggers the contraction of the T cell response after antigen elimination?
What triggers the contraction of the T cell response after antigen elimination?
What is a key mechanism behind the decline of T cell responses?
What is a key mechanism behind the decline of T cell responses?
Which statement regarding the characteristics of memory T cells is correct?
Which statement regarding the characteristics of memory T cells is correct?
How do effector cells give rise to memory T cells?
How do effector cells give rise to memory T cells?
Which of the following is NOT a factor contributing to the decline of T cell responses?
Which of the following is NOT a factor contributing to the decline of T cell responses?
What is the significance of having a greater number of memory T cells compared to naive T cells?
What is the significance of having a greater number of memory T cells compared to naive T cells?
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Study Notes
Dendritic Cells and T Cell Activation
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Dendritic cells are essential for presenting antigens to T cells. They capture antigens from the environment and migrate to lymph nodes where they interact with T cells.
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Signal 1 - Antigen recognition by the T cell receptor (TCR) is essential for T cell activation. This involves the T cell recognizing a specific antigen presented by the dendritic cell.
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Signal 2 - CD40L:CD40 interactions provide the second signal for T cell activation. CD40L on the T cell binds to CD40 on the dendritic cell, leading to the activation and maturation of the dendritic cell. This results in the increased expression of co-stimulatory molecules like B7.
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CTLA-4:B7 interactions suppress T cell activation. CTLA-4, expressed on activated T cells, competes with CD28 for binding to B7. This interaction delivers an inhibitory signal, dampening T cell activation.
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PD-1 plays a regulatory role by inhibiting T cell activation. It binds to its ligands, PD-L1 and PD-L2, which are expressed on various cells, including tumor cells. This interaction leads to the inhibition of T cell signaling and a reduction in T cell function.
T Cell Co-Stimulatory Pathways and Therapies
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CD40L:CD40 pathway is targeted in clinical trials for its potential in cancer immunotherapy. Therapies blocking the CD40 pathway are being investigated for their ability to enhance antitumor immunity.
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Therapeutic costimulatory blockade, such as CTLA-4 or PD-1 blockade, achieves therapeutic effects by regulating T cell activity. This approach involves blocking inhibitory pathways, allowing T cells to mount a robust response against tumors or pathogens.
IL2: Key Cytokine in T Cell Responses
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IL-2, a key cytokine in T cell responses, is primarily produced by activated T cells. It promotes the growth and differentiation of T cells, enhancing their immune functions.
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CD69 is predominantly expressed on activated T cells. It acts as a marker of activation and its expression is upregulated after T cell stimulation.
T Cell Clonal Expansion and Differentiation
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Clonal expansion refers to the rapid proliferation of activated T cells, creating a large number of identical cells specific for the recognized antigen.
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Foxp3 is crucial for the differentiation and function of regulatory T cells (Tregs). Tregs play a critical role in suppressing immune responses, maintaining tolerance, and preventing autoimmune reactions.
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IL-2 influences the activity of other T cells by promoting the differentiation of effector T cells and supporting the survival and function of Tregs.
Changes in Surface Molecule Expression following T Cell Activation
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Downregulation of CCR7 expression is a key change in surface molecule expression following T cell activation which aids in T cell migration to inflammatory sites.
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CD28 is a surface molecule typically associated with the costimulatory signal necessary for T cell activation. It binds to B7 on antigen-presenting cells, providing the required second signal for T cell activation.
IL-2 Secretion and Adhesion Molecules in T Cell Activation
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Activated T cells are the primary source of IL-2 secretion in the early phase of T cell activation. This IL-2 is crucial for their own proliferation and differentiation into effector cells.
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Adhesion molecules, like LFA-1, facilitate the tight interaction between T cells and antigen-presenting cells. These interactions are essential for the delivery of activation signals and effective immune responses.
Memory T Cells: Properties and Differentiation
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Memory T cells exhibit increased expression of anti-apoptotic proteins, which contributes to their prolonged survival and allows them to respond rapidly upon encountering the same antigen.
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Memory T cells display more rapid and robust responses to antigen stimulation compared to naive T cells, enabling a quicker and more effective immune response upon re-exposure to the same pathogen.
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Cytokines like IL-7 are crucial for the maintenance of memory T cells in the absence of antigen. They provide survival signals and maintain the pool of memory T cells, ensuring a rapid response upon subsequent encounters with the pathogen.
Contraction of T Cell Responses and Memory T Cell Generation
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Elimination of the antigen triggers the contraction of the T cell response. This involves the removal of effector T cells, reducing the immune response to manageable levels.
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A key mechanism behind the decline of T cell responses is the death of activated T cells due to the lack of antigenic stimulation and the withdrawal of survival signals. This ensures that immune responses are controlled and do not persist indefinitely.
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Memory T cells are long-lived and exhibit enhanced survival, allowing them to persist even after the antigen is cleared. This provides rapid and effective immune responses upon re-exposure to the same pathogen.
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Effector cells contribute to the generation of memory T cells. This is achieved through various mechanisms, including the expression of specific transcription factors and the retention of survival signals.
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A greater number of memory T cells compared to naive T cells signifies a more robust and efficient immune response upon reencountering the same antigen. This enables a quicker and more effective defense against previously encountered pathogens, contributing to a more resilient immune system.
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