26 Questions
Which receptor recognizes B7 on APCs, generating signals for T cell activation?
CD28
Why is costimulation necessary for the full activation of naïve T lymphocytes?
To ensure activation by microbial antigens only
Which molecules are critical for limiting and terminating immune responses according to the text?
CTLA-4 and PD-1
When are the expressions of B7-1 and B7-2 increased on APCs?
When encountering microbes
What is the main function of CTLA-4 and PD-1 in response to tumors and chronic viral infections?
Inhibiting immune responses
Which type of cells mainly secrete cytokines in adaptive immunity?
CD4+ effector cells
What is the principal function of IL-2 in T cell growth?
Promoting survival and proliferation of T cells
How does the activation of CD8+ T cells often occur?
Through the ingestion of virus-infected cells by dendritic cells
What is the role of CD4+ helper T cells in activating CD8+ T cells?
Secrete IL-2 to help activate CD8+ T cells
What costimulatory molecule do APCs express that plays a role in T cell activation?
B7
What is essential for the activation of naïve T cells?
Binding of T cell receptors to MHC molecules
Which molecules must bind for effective costimulation of T cells?
CD28 and B7-1 or B7-2
What are the two main signals required to activate naïve T cells?
TCR binding to MHC and costimulatory receptor binding
What happens if T cells are activated without co-stimulation?
T cell deletion or immune tolerance
Which receptors help the TCR complex deliver activating signals during T cell activation?
CD4 and CD8 coreceptors
Which step is crucial for differentiating between self and non-self molecules by lymphocytes?
TCR recognition of antigens
'Clonal expansion' in the context of the immune response refers to what process?
'Division' phase of activated T cells after antigen recognition
What is the main effect of the interaction between CD40L on antigen-stimulated T cells and CD40 on DCs?
Increased expression of costimulators on APCs
Which agent is being tested for blocking interactions between CD40L and CD40 in inflammatory diseases?
Antibodies
Which cytokines may keep memory T cells alive?
IL-15 and IL-7
What is a key characteristic of memory T cells?
They are rapidly induced to produce cytokines upon initial exposure to antigen
What effect does CD40L:CD40 binding have on APCs?
Activates APC to express cytokines such as IL-12
What is the main function of CTLs in immune response?
Kill infected cells by direct contact
What characterizes the expansion of CD4+ T cells compared to CD8+ T cells?
CD4+ T cell expansion is 100-1000-fold lesser than that of CD8+ T cells
What leads to the differentiation of effector T cells?
Changes in gene expression such as cytokine gene activation
What is the primary role of costimulation in T cell activation?
Enhancing activation and differentiation of T cells
Study Notes
Activation of T Cells
- T cell activation requires two signals: antigen recognition through T cell receptor (TCR) binding to MHC-peptide complex and costimulation through CD28-B7 (CD80/CD86) binding
- CD28 binds to B7-1 (CD80) and B7-2 (CD86) on antigen-presenting cells (APCs), generating signals that work together with TCR recognition
- CD4+ and CD8+ T cells require costimulation for full activation
Inhibitory Receptors
- Inhibitory receptors, such as CTLA-4 and PD-1, are involved in limiting and terminating immune responses
- CTLA-4 recognizes B7-1 (CD80) and B7-2 (CD86) on APCs, while PD-1 recognizes different ligands on many cell types
- These receptors are involved in inhibiting responses to tumors and chronic viral infections
Recognition of MHC-Antigen Complex and Costimulators
- Naive T cells have a low level of protein synthesis, which is increased upon antigen recognition and costimulation
- The synapse is the site of delivery of activating signals from membrane receptors to the cell's interior
- Effector molecules and cytokines may be secreted through this region, ensuring targeted delivery to the APC
Secretion of Cytokines and Expression of Cytokine Receptors
- CD4+ effector cells secrete cytokines, including IL-2, which stimulates survival and proliferation of T cells
- CD4+ cells express high-affinity IL-2 receptors, enhancing their ability to bind and respond to IL-2
- Stimulated CD8+ cells do not secrete large amounts of IL-2, which may be provided by CD4+ helper T cells
CD4+ Helper T Cells and CD8+ T Cell Activation
- CD4+ helper T cells play a role in the activation of CD8+ T cells, enhancing their survival and proliferation
- CD4+ cells produce cytokines or membrane molecules that help activate CD8+ cells
- Defective CTL responses to viruses in HIV-infected patients may be due to the loss of CD4+ helper T cells
APCs Express Costimulatory Molecules
- APCs express costimulatory molecules, such as B7-1 and B7-2, which bind to CD28 on T cells
- CD40L-CD40 binding leads to the upregulation of costimulatory molecules on APCs and the production of cytokines, enhancing T cell activation
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