T Cell Development and Activation

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Questions and Answers

What is the primary location where T cell precursors complete their maturation?

Spleen

Bone marrow

Lymph nodes

Thymus (correct)

Which process allows T cells to recognize self-MHC during their development?

Negative selection

Positive selection (correct)

T cell activation

Co-receptor selection

What happens to thymocytes that do not recognize an MHC molecule within 3-4 days of initial expression?

They become activated

They die (correct)

They migrate to the spleen

They undergo positive selection

Which cells mediate positive selection in the thymus?

Cortical epithelial cells Signup and view all the answers

What is the outcome for CD4LOW CD8HIGH thymocytes that recognize MHC class I molecules?

They survive Signup and view all the answers

What is a characteristic of thymocytes that survive both positive and negative selection?

They are self-tolerant naive T cells Signup and view all the answers

In which part of the thymus does negative selection primarily take place?

Both cortex and medulla Signup and view all the answers

Which cell types play a role in negative selection of thymocytes?

Cortical epithelial cells and dendritic cells Signup and view all the answers

What primarily influences the survival or death of thymocytes during selection?

Binding affinity to MHC-peptide complexes Signup and view all the answers

What is the role of co-receptor downregulation during T cell development?

To enable selection of specific T cell lineages Signup and view all the answers

What role does IL-2 play in T cell activation?

It facilitates the proliferation and differentiation of T cells. Signup and view all the answers

Which process ensures that T cells recognize self-MHC molecules during their development?

Positive selection allows only T cells that bind to self-MHC. Signup and view all the answers

What determines the type of effector T cell that a T cell will become?

The presence of specific cytokines expressed by APCs. Signup and view all the answers

During T cell activation, what is the significance of the co-stimulatory signal B7:CD28?

It enhances T cell survival and proliferation. Signup and view all the answers

What is the primary role of T cells in immune defense?

Attacking intracellular pathogens and cancerous cells. Signup and view all the answers

What is the significance of cell adhesion molecules (CAMs) in T cell activation?

They allow for stable interactions between T cells and APCs. Signup and view all the answers

What characterizes the transition of naive T cells to effector T cells?

Clonal expansion triggered by antigen and co-stimulation. Signup and view all the answers

What is the first step in T cell activation?

Recognition of antigen presented by MHC molecules. Signup and view all the answers

Which T cell subset is primarily associated with helping other immune cells?

CD4+ helper T cells. Signup and view all the answers

What physiological process occurs during T cell activation following antigen recognition?

Entry into the cell cycle and clonal expansion. Signup and view all the answers

Study Notes

T Cell Development and Activation

T cells develop from hematopoietic stem cells in the bone marrow, but complete maturation in the thymus.
The thymus is divided into lobules with a cortex and medulla.
Development stages are identified by the presence/absence of cell-surface markers (TCR, CD3, CD4, CD8).
T-cell precursors proliferate extensively in the thymus, and most die there.
T cells differentiate into two lineages: γ:δ and α:β.
α:β T cells further distinguish into CD4+ and CD8+ T cells.
T cells that recognize self-MHC (positive selection) and are self-tolerant (negative selection) are generated.

Learning Objectives

Describe the stages of T cell development from hematopoietic stem cells in the bone marrow to mature T cells.
Recognize positive and negative selection in T cell development.
Describe the process of T cell activation.
Understand T cell-mediated immune responses.

Positive Selection

Occurs in the thymic cortex.
Mediated by thymic cortical epithelial cells expressing MHC class I and II proteins.
Thymocytes that do not recognize MHC molecules within 3-4 days of α:β expression die.
Successful recognition by cortical epithelial cells results in a survival signal.

Co-receptor Selection

Recognition of an MHC molecule by one co-receptor results in downregulation of the other co-receptor gene.
CD4^lowCD8^high cells survive if they recognize MHC class I molecules.
CD4^highCD8^low cells survive if they recognize MHC class II molecules.
Co-receptor recognition by epithelial cells triggers a maturation signal.

Negative Selection

Occurs in the thymic cortex and medulla.
Mediated by cortical epithelial cells, macrophages, and dendritic cells.
Thymocytes that strongly recognize self-peptide:MHC complexes die.
Different binding affinities to MHC-peptide drive survival or death (positive/negative selection).
Self-peptides are derived from thymic and ubiquitous blood proteins.
T cells that successfully complete positive, co-receptor, and negative selection are single positive, self-tolerant, naïve T cells.

T Cell Activation

Antigen recognition occurs on antigen-presenting cells (APCs) by MHC-peptide complexes.
Co-stimulatory signals are delivered (e.g., B7:CD28).
T cells enter the cell cycle (G1) for proliferation, known as clonal expansion.
Interleukin-2 (IL-2) mediates proliferation and differentiation into effector cells.
Cytokines expressed by APCs determine the effector T cell type.

T Cell-Mediated Immunity

Naive T cells circulate between blood and lymphoid tissues.
Activation occurs via antigen co-stimulation and recognition of MHC-peptide complexes on APCs.
Cell adhesion molecules (CAMs) mediate the process.
T cells monitor MHC-peptide complexes within lymphoid tissue.

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Description

Explore the intricate process of T cell development, including their origin in the bone marrow and maturation in the thymus. This quiz covers the stages of differentiation, positive and negative selection, and the mechanisms behind T cell activation and immune responses. Test your knowledge on these essential components of the immune system.