B Cell Development and Antigen Recognition

Questions and Answers

What is the composition of the antigen binding site formed by B cell receptors?

One variable and one constant domain

Two variable regions from heavy and light chains (correct)

Three constant domains from heavy chains

Only heavy chain variable regions

Which step in B cell maturation involves the expression of the pre-BCR?

Mature B cell

Pre-B cell (correct)

Immature B cell

Pro-B cell

What type of B cells undergo positive selection?

B cells that have not rearranged their heavy chain locus

B cells with low-affinity receptors

B cells expressing functional Ig molecules (correct)

Self-reactive B cells

What occurs during negative selection of B cells?

B cells with high avidity to self antigens undergo cell death Signup and view all the answers

What characterizes follicular B cells?

They migrate between lymphoid organs and reside in B cell follicles Signup and view all the answers

Which Ig molecules do mature B cells express as antigen receptors?

IgM and IgD Signup and view all the answers

What is the main outcome of positive selection in the thymus?

Promotion of T cells that can recognize self peptide with weak affinity Signup and view all the answers

What is a defining feature of marginal zone B cells?

They are located in the marginal sinus of the spleen Signup and view all the answers

What is the primary function of plasma cells derived from activated mature B cells?

They secrete specific antibodies into the bloodstream Signup and view all the answers

What occurs during negative selection of T cells?

Elimination of harmful self-reactive T cells through apoptosis Signup and view all the answers

Which chains form the T cell Antigen Receptor (TCR)?

Two peptide chains, α and β Signup and view all the answers

Which of the following cells are considered professional antigen presenting cells (APCs)?

B lymphocytes Signup and view all the answers

What is a distinguishing feature of MHC class I molecules?

Expressed on all nucleated body cells Signup and view all the answers

What is the role of CD3 in T cell activation?

To promote signal transduction and stabilize TCR Signup and view all the answers

What is a feature of the B cell Antigen Receptor (BCR)?

Ig-α/Ig-β heterodimers associate with the membrane Ig Signup and view all the answers

What components are involved in the structure of MHC class II molecules?

Two polypeptide chains, α and β Signup and view all the answers

What distinguishes the light chains in B cell Antigen Receptors (BCRs)?

They can be either kappa or lambda chains Signup and view all the answers

In the endocytic pathway for MHC class II antigen processing, where are exogenous antigens degraded?

In the endosomal vesicles Signup and view all the answers

Which type of T cell interacts with MHC class I molecules?

CD8+ T cells Signup and view all the answers

How do immature T cells differentiate into CD4+ or CD8+ T cells?

By expressing both CD4 and CD8 during development Signup and view all the answers

Which statement best describes the peptide binding site of MHC class I molecules?

Located within a groove between α1 and α2 domains Signup and view all the answers

What ensures the stability of the T cell receptor during activation?

The presence of CD3 in the complex Signup and view all the answers

What type of antigens do MHC class II molecules present?

Exogenous antigens only Signup and view all the answers

What is the primary processing machinery used for MHC class II antigen presentation?

Lysosomal enzymes Signup and view all the answers

Which of the following molecules assists in the structure of MHC class I?

β2 microglobulin Signup and view all the answers

What type of cells present antigens through MHC class I?

All nucleated cells Signup and view all the answers

Which pathway is responsible for the presentation of peptides derived from cytosolic proteins?

Cytosolic pathway Signup and view all the answers

Which of the following best describes the antigen source for MHC class I presentation?

Cytosolic proteins of host or intracellular pathogens Signup and view all the answers

Which T cell type requires the presence of MHC class II molecules to recognize foreign peptides?

CD4+ T cells Signup and view all the answers

In which type of antigen processing pathway does MHC class II play a role?

Endocytic pathway Signup and view all the answers

What is the major source of antigen for MHC class I presentation?

Cytosolic proteins of host or intracellular pathogens Signup and view all the answers

Which statement about MHC/T cell interactions is true?

CD8+ T cells are restricted to recognizing antigens presented by MHC class I. Signup and view all the answers

What is a primary function of CD4 T helper cells?

Activate cytotoxic T cells Signup and view all the answers

Which of the following best describes the role of B7 in T cell activation?

It acts as a costimulatory molecule for T cell receptor signaling. Signup and view all the answers

What is the end result of T cell activation?

Clonal expansion and development of effector cells Signup and view all the answers

Which subset of T cells is involved in the early immune response by differentiating from naive T0 cells?

TH1 cells Signup and view all the answers

How do effector T cells reach the site of infection?

They express adhesion molecules and chemokine receptors. Signup and view all the answers

What type of cells do TH2 cells primarily assist in activating?

B lymphocytes Signup and view all the answers

Which statement best describes TH17 cells?

They play a role in autoimmunity. Signup and view all the answers

What interaction is crucial for the activation of T cells via CD40L?

Interaction with CD40 on antigen presenting cells Signup and view all the answers

Study Notes

Thymus Functionality

Positive Selection: Promotes survival of T cells with TCRs that recognize self peptides with weak affinity, enabling recognition of foreign antigens.
T Cell Differentiation: Immature T cells expressing both CD4 and CD8 differentiate into CD4+ T cells or CD8+ T cells.
Negative Selection: Eliminates immature T cell clones with strong affinity for self antigens in the thymus through apoptosis, maintaining self-tolerance and preventing autoimmunity.
Naïve T Cell Migration: Mature, immunocompetent T cells enter circulation and peripheral lymphoid tissues.

Structure of T Cell Antigen Receptor (TCR)

TCR Composition: Composed of two peptide chains, α and β.
Binding Sites: The α1 and β1 domains (V domains) form the antigen binding site, while α2 and β2 (C domains) are constant regions.
CD3 Complex: The α/β dimer associates with CD3, which is essential for TCR expression and signaling activation.

Structure of B Cell Antigen Receptor (BCR)

BCR Configuration: Consists of a single IgM molecule on the B cell surface, often with IgD in mature B cells.
Heterodimers: Ig-α/Ig-β heterodimers associate with the membrane Ig subunits.
Light and Heavy Chains: Comprised of two heavy chains and two light chains; light chains include kappa (κ) and lambda (λ) types, while heavy chains contain one variable and three constant domains.

Steps of B Cell Maturation in Bone Marrow

Pro-B Cells: Initial recombination of Ig genes at the heavy chain locus.
Pre-B Cells: Express heavy chains mu (μ) of IgM for pre-BCR formation.
Immature B Cells: Express a complete IgM molecule, consisting of two heavy and two light chains (κ).
Positive Selection: Functional membrane Ig molecules receive survival signals.
Negative Selection: High avidity self-receptor expressing B cells undergo clonal deletion.
Mature B Cells: Leave bone marrow, express IgM and IgD, secrete antibodies as plasma cells upon activation.

Subsets of Mature B Cells

Follicular B Cells: Majority of mature B cells, express IgD, migrate between lymphoid organs.
Marginal Zone B Cells: Located in the spleen, respond rapidly to blood-borne microbes, differentiate into short-lived plasma cells.

Cell Mediated Immunity (CMI)

Professional APCs: Include macrophages, dendritic cells, and B lymphocytes that process antigens and present peptide fragments via MHC molecules.

MHC Molecules

MHC Classification: Divided into Class I (all nucleated cells) and Class II (immune cells only).
Class I Structure: Comprises a heavy chain complexed with β2 microglobulin, presenting peptides to CD8+ TC cells.
Class II Structure: Forms from two polypeptide chains with a peptide-binding site for CD4+ TH cells.

Antigen Processing and Presentation

Endocytic Pathway (Class II): Exogenous antigens are internalized, degraded, and presented to CD4+ T helper cells.
Cytosolic Pathway (Class I): Endogenous proteins are degraded and presented to CD8+ cytotoxic T cells.

T Cell Activation

T Cell Subsets: Include CD4+ T helper cells (TH1, TH2, TH17, Tregs) and CD8+ T cytotoxic cells.
Activation Signals:
- First Signal: Antigen recognition via MHC-TCR interaction.
- Second Signal: Costimulatory signals through CD28-B7 interaction and CD40-CD40L engagement.

Migration of Effector T Cells

Adhesion Molecules: Allow effector T cells to migrate to infection sites via blood vessels, following chemokine signals.

Functions of TH1 Cells

Differentiation Inducers: IL-12 and INF-gamma promote differentiation of naive TH0 into TH1 cells during an early immune response.

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Description

This quiz explores the key concepts related to B cell receptors, their maturation, and the selection processes they undergo. It covers the composition of antigen binding sites, the role of pre-BCR, and the characteristics of different types of B cells. Test your understanding of immunology related to B cell function and development.