Adaptive Immunity III: T Cell Development

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Questions and Answers

What is the basic structure of the T cell receptor?

Two identical alpha chains

Two identical beta chains

Three monovalent chains

One alpha chain and one beta chain (correct)

Which process ensures that T cell receptors are appropriate for the host's MHC?

Positive selection (correct)

Negative selection

Gene rearrangement

Clonal expansion

Which of the following correctly describes CD3 in T cells?

An exclusive component of B cell receptors

Only expressed on activated T cells

A component of the T cell receptor complex that mediates activation (correct)

A polymorphic receptor present only on CD8 T cells

What type of genetic arrangement occurs at the T cell receptor gene loci?

Independent rearrangements at alpha and beta loci Signup and view all the answers

Which of the following describes a potential outcome of negative selection in the thymus?

Deletion of T cells that bind too strongly to self-antigens Signup and view all the answers

Which aspect of T cell development primarily occurs in the thymus?

T cell receptor expression Signup and view all the answers

How does allelic restriction differ from MHC class restriction in T cells?

MHC class restriction refers to the class of MHC that presents the antigen. Signup and view all the answers

What is the relationship between T cell receptor specificity and major T cell subclasses?

Different subclasses have distinct receptor specificities based on antigen recognition. Signup and view all the answers

What is the primary function of positive selection in T cell development?

To ensure interaction with self-MHC molecules Signup and view all the answers

Which T cell subset is primarily restricted to MHC class I?

CD8+ T cells Signup and view all the answers

How does negative selection contribute to self-tolerance in T cells?

By deleting T cells that bind too strongly to self-antigens Signup and view all the answers

What is the role of MHC molecules in T cell activation?

To present both self and foreign antigens to T cells Signup and view all the answers

What characterizes the allelic variation of MHC molecules in a population?

Extensive polymorphism with numerous variants Signup and view all the answers

Which cytokine can induce the expression of MHC class II molecules on other cells?

Interferon-g Signup and view all the answers

What is the significance of affinity selection for TCRs during thymic development?

It creates TCRs with varying affinities for self-MHC molecules Signup and view all the answers

Which characteristic applies to both CD4+ and CD8+ T cells?

They interact with MHC molecules for antigen recognition Signup and view all the answers

What is primarily recognized by T cell receptors during immune response?

Peptides bound to MHC molecules Signup and view all the answers

Which T cell subtype is primarily involved in promoting B cell activation?

TH2 Signup and view all the answers

What determines the class of MHC molecule a T cell receptor recognizes?

Expression of CD4 or CD8 Signup and view all the answers

What leads to the anergy of autoreactive T cells?

Binding to self-antigens on non-antigen-presenting cells Signup and view all the answers

Which of the following activities is a direct function of CD4+ T cells?

Cytokine release to coordinate immune response Signup and view all the answers

What is a consequence of the lack of CD40L-CD40 interaction?

No isotype switching occurs Signup and view all the answers

Which class of MHC molecules do CD8+ T cells recognize?

MHC Class I Signup and view all the answers

What is the primary role of regulatory T cells (Treg) in the immune system?

Suppressing immune responses Signup and view all the answers

Study Notes

Adaptive Immunity III: Clonal Selection Theory and T Cell Development

T cell antigen receptor gene loci are arranged in a general germline fashion
T cell receptors have a specific structure and are expressed on the cell surface
Positive and negative selection events in the thymus influence T cell receptor repertoire and impose MHC restriction
MHC molecules exhibit diversity at individual and population levels
The relationship between the MHC antigen presentation pathway, T cell receptor specificity, and major T cell subsets is described
Major T cell functions and their relationship to receptor specificity are listed
The differences between MHC class restriction and allelic restriction for T cells are explained

T Cell Receptor Structure

The clonotypic receptor is composed of alpha and beta chains, making it monovalent
The receptor is associated with CD3 signaling molecules, forming a complex
CD3 is non-polymorphic and found on all T cells
The complex senses receptor binding and initiates activation signaling

Germ-Line Configuration of T Cell Receptor Genes

Independent gene rearrangements occur in alpha and beta loci
Pairing of alpha and beta chains occurs after rearrangements
Germ-line DNA undergoes recombination to form functional T cell receptors

T Cell Development

T cell progenitors leave the bone marrow and travel to the thymus, becoming thymocytes.
Key events in T cell development within the thymus include: gene rearrangement, TCR expression, positive selection (appropriate TCR for host MHC), and negative selection(self-reactive TCR)
T cells develop through various stages: double-negative, double-positive, and single-positive.

MHC Molecules - Classes, Categories, and Alleles

MHC molecules are categorized into class I and II
MHC class I molecules are expressed on all nucleated host cells
MHC class II molecules are mostly expressed on specialized antigen-presenting cells
MHC molecules have diverse allelic variants within a population

Effects of Thymic Selection

Positive selection ensures interaction with self-MHC molecules (MHC restriction)
T cell subset selection is based on TCR binding to MHC class I (CD8+) or II (CD4+)
Negative selection deletes autoreactive T cells (self-tolerance)
The selected T cell repertoire has a narrow range of affinities for self-MHC molecules

What Makes T Cells Work?

Affinity for self-MHC meets a threshold for selection and survival in the thymus, creating T lymphocytes with receptors specific for the host's MHC alleles
A diverse T cell receptor repertoire ensures that when a foreign peptide binds to an MHC molecule, the affinity of some T cell receptors will increase above the threshold for activation
Activation leads to proliferation, differentiation, and acquisition of effector functions

Function of T Cell Matched to Class of MHC Restriction

MHC class I molecules present endogenous antigens, interacting with CD8+ T cells (cytotoxic T cells)
MHC class II molecules present exogenous antigens, interacting with CD4+ T cells (helper T cells)
Different types of CD4+ T cells coordinate the immune response

What Does MHC Restriction Look Like?

Peptides bind to specialized grooves in MHC molecules.
Longer grooves in MHC class II bind longer peptides
T cell receptors recognize peptides and polymorphic residues on MHC molecules

Regulation of Autoreactive B and T Cells not Deleted

Autoreactive B cells may be denied helper T cell aid leading to B cell anergy
Autoreactive T cells may not be able to engage specialized APCs,leading to T cell anergy.
In cases where mechanisms for preventing autoreactivity fail, interventions may sometimes be needed.

Summary

Naïve T cells leave the thymus expressing CD3, CD4 or CD8 and a T cell receptor
Selection processes impose MHC restriction and self-tolerance
T cell expression of CD4 or CD8 defines the class of MHC molecules it recognizes
T cell functions are associated with the recognized MHC class
Specialized antigen-presenting cells are vital for naïve T cell activation
Cell-to-cell contact is essential for activated helper T cells and B cells to produce isotype switching and somatic hypermutation.

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Description

Explore the intricate mechanisms of T cell development, including the clonal selection theory and the role of MHC molecules. Learn about T cell receptor structure, selection processes in the thymus, and the functional specificity of major T cell subsets. This quiz delves into important concepts that define adaptive immunity and T cell responses.