5. T cells II Flashcards
(23 cards)
What is the first signal in the T cell activation process?
T cell receptor (TCR) recognizes antigen presented on MHC molecules
This initial recognition is crucial for T cell activation.
What is the role of CD28 in T cell activation?
CD28 binds to B7 molecules (CD80/CD86) on antigen-presenting cells for co-stimulation
This co-stimulation promotes IL-2 production and enhances T cell function.
What is the purpose of cytokines in T cell activation?
Cytokines and environmental factors shape the specific response of T cells
They are essential for directing the immune response.
What occurs during the initial contact of T cells with APCs?
T cells use integrins (LFA-1) to bind APCs via ICAM molecules for brief scanning
This interaction lasts about 2-3 seconds.
What forms during the stable interaction between T cells and APCs?
An immunological synapse forms, reorganizing cell machinery and receptors
This interaction lasts 12-24 hours for full activation.
What is the effect of positive co-stimulation on T cells?
Promotes IL-2 production, cell proliferation, and function
Critical for T cell survival and activity.
What is the function of CTLA-4 in T cell regulation?
CTLA-4 inhibits T cell responses by outcompeting CD28 for B7 molecules
This negative co-stimulation is important in controlling immune responses.
What happens to T cells without co-stimulation?
T cells become ‘anergic’ (unresponsive) despite antigen recognition
This prevents inappropriate immune activation.
Where does primary T cell activation occur?
In lymphoid organs such as lymph nodes and spleen
The human body has approximately 250 lymph nodes.
What types of cells are found in lymph nodes?
T cell zones, B cell follicles, and germinal centers
These areas facilitate interactions between T cells and dendritic cells.
What is the sequence of events in T cell activation after a viral infection?
- Virus infects cells
- Infected cells die, releasing antigens
- Dendritic cells uptake antigens
- Dendritic cells travel to lymph nodes
- T cells scan dendritic cells
- Recognition leads to activation and proliferation
- Activated T cells leave lymph nodes
- T cells kill infected cells
This sequence highlights the immune response to infections.
What is the primary function of CD8+ T cells?
Directly kill infected or cancerous cells
They express CD8 co-receptor that binds MHC class I.
How do CD8+ T cells kill target cells?
By releasing perforin and granzymes after forming an immunological synapse
This mechanism triggers apoptosis in target cells.
What is the role of CD4+ T cells in the immune response?
Produce cytokines that coordinate immune responses and activate other immune cells
They express CD4 co-receptor that binds MHC class II.
What are the main subsets of CD4+ T cells?
- Th1 cells
- Th2 cells
- Th17 cells
- Regulatory T cells (Tregs)
Each subset has specialized functions in the immune response.
What cytokines induce Th1 cells?
Induced by IL-12
Th1 cells combat intracellular pathogens.
What is the primary function of Th2 cells?
Combat extracellular parasites and activate mast cells
Induced by IL-4, they drive allergic responses.
What do Th17 cells primarily combat?
Fungal infections
They are also implicated in various autoimmune diseases.
What is the significance of regulatory T cells (Tregs)?
Suppress other T cell responses to prevent autoimmunity
They express Foxp3 transcription factor.
What happens to most effector T cells after pathogen clearance?
Most die, but a small portion survives as memory T cells
Memory T cells provide long-lasting protection.
How long can memory T cells persist?
For decades without requiring re-exposure to antigen
They respond more rapidly than naive T cells.
Why is regulating T cell function important?
To prevent autoimmunity and excessive immune responses
T cells can cause damage if not properly regulated.
What are some mechanisms that ensure T cell regulation?
- Thymic selection
- Requirement for co-stimulation
- Negative regulatory molecules (CTLA-4, PD-1)
- Regulatory T cells
These mechanisms are essential for maintaining immune balance.
