02 Adaptive Immune System: B-cell activation and differentiation

Questions and Answers

What is the role of the enzyme activation-induced deaminase (AID) in B cell differentiation?

It helps in the proliferation of plasma cells.

It activates the T cell response.

It breaks down the VDJ region in the DNA.

It removes the constant region between VDJ and antibody. (correct)

How long do most mature B cells survive in the lymphatic system without encountering an antigen?

2 months

1 week

6 months (correct)

1 year

What is the lifespan of plasma cells that have encountered their antigen and developed from B cells?

1 month

4 weeks

8 weeks

6 weeks (correct)

Which statement is true regarding the differentiation of B cells into plasma cells?

Plasma cells are produced only from stimulated B cells. Signup and view all the answers

What allows a fully differentiated plasma cell to have surface-bound IgG despite producing antibodies?

Alternative splicing. Signup and view all the answers

What is the primary role of B cell receptors in the adaptive immune response?

To bind specific antigens and initiate immune responses. Signup and view all the answers

Which of the following correctly describes the structure of a B cell receptor?

It has two identical heavy chains and two identical light chains. Signup and view all the answers

What is the significance of the Fab region in a B cell receptor?

It contains the binding sites for antigens. Signup and view all the answers

During the development of a B cell, which heavy chain is initially expressed?

IgM Signup and view all the answers

How many identical antigen binding sites does each B cell receptor have?

Two Signup and view all the answers

What structural component links the heavy and light chains of a B cell receptor?

Disulfide bonds Signup and view all the answers

What happens to the B cell receptor as the cell transforms into a plasma cell?

It gets secreted as an antibody. Signup and view all the answers

What are the five major types of heavy chains associated with immunoglobulin isotypes?

Mu, delta, gamma, alpha, epsilon Signup and view all the answers

What is the result of alternative splicing in mature B cells?

The simultaneous expression of IgM and IgD Signup and view all the answers

Which structure do B cells migrate to after entering the lymph node?

Cortical region Signup and view all the answers

What must occur for a B cell to become activated?

Crosslinking of the B cell receptors Signup and view all the answers

Which of the following molecules helps initiate B cell activation in conjunction with the B cell receptor?

CD21 (CR2) Signup and view all the answers

Upon activation, what type of antibody does the B cell secrete initially?

IgM Signup and view all the answers

How does isotype switching affect IgM production in B cells?

IgM production stops completely after switching Signup and view all the answers

Which transcription factors are activated upon phosphorylation of the ITAMs in B cells?

NFkappaB and NFAT Signup and view all the answers

What role do high endothelial venules (HEVs) play in the lymphatic system?

Allow lymphocytes to enter lymph nodes from the blood Signup and view all the answers

What specific amino acids are crucial within the ITAM for B cell activation?

Tyrosine and Tyrosine Signup and view all the answers

What happens when CD40 on a B cell interacts with CD40L on an activated T cell?

Cytokine receptors are expressed on the B cell's surface Signup and view all the answers

What is the role of the immune receptor tyrosine-based activation motif (ITAM) in B cells?

To transmit activation signals following receptor crosslinking Signup and view all the answers

Which cytokines promote a B cell's differentiation into an IgE secreting plasma cell?

IL-4 and IL-5 Signup and view all the answers

Which process does NOT occur once a B cell is activated?

Differentiation into a memory cell Signup and view all the answers

What is the consequence of C3d binding to CD21 on B cells?

Enhancement of B cell activation alongside receptor binding Signup and view all the answers

Study Notes

Immune Response and Lymphocytes

Immune response is highly specific for each invader via unique receptors on adaptive immune cells.
Key players in adaptive immunity are lymphocytes: B cells and T cells.

Development and Structure of B Cells

B cells develop in the bone marrow through VDJ rearrangement, creating a diverse set of B cell receptors (BCRs).
B cell receptors function as antibodies with a transmembrane component, consisting of two heavy chains and two light chains.
The fragment-antigen binding (Fab) region of the BCR binds to antigens, while the constant region (Fc) remains unchanged.
Heavy chains are linked by disulfide bonds, and each BCR has two identical binding sites.

Isotypes and Alternative Splicing

Five major classes of immunoglobulins defined by heavy chain types: IgM, IgD, IgG, IgA, and IgE.
Initially, developing B cells express mu heavy chains, resulting in surface IgM.
Alternative splicing allows simultaneous expression of IgM and IgD, characterizing mature but naive B cells.

Antigen Exploration and Activation

Mature B cells travel through lymph nodes, searching for antigens and interacting with various immune cells.
Entrance into lymph nodes can occur via afferent lymphatic vessels or high endothelial venules (HEVs).
B cells migrate to the cortical region and can form primary lymphoid follicles, potentially leading to germinal center formation upon activation.

B Cell Activation Mechanisms

B cells recognize diverse antigens, including peptides, carbohydrates, and lipids in their native forms.
Antigen crosslinking of BCRs triggers activation through clustering of intracellular chains (Ig alpha, Ig Beta, CD19).
Immune receptor tyrosine-based activation motifs (ITAMs) undergo phosphorylation by specific protein kinases (Blk, Fyn, Lyn).

Cytokines and Proliferation

Activated B cells express key transcription factors like NFkappaB and NFAT, leading to cytokine production (IL-1, IL-2, IL-6, TNF alpha) and upregulation of anti-apoptotic markers (Bcl-2).
CD21 (CR2) binds to complement fragment C3d, facilitating B cell activation alongside BCR signaling.

Plasma Cell Differentiation and Isotype Switching

Activated B cells differentiate into plasma cells, primarily secreting IgM antibodies.
Interaction with CD4+ T cells can induce class switching to produce other antibody isotypes, requiring DNA rearrangement.

Role of T Cells in B Cell Activation

B cells present antigens on MHC class II to CD4+ T cells, which, upon activation, express CD40L.
CD40-CD40L interaction prompts B cells to express cytokine receptors and respond to T cell cytokines for specific antibody production.

Life Cycle of B Cells and Plasma Cells

Mature B cells have a typical lifespan of around 6 months in the lymphatic system without antigen stimulation.
Plasma cells, which produce antibodies, survive roughly 6 weeks and do not divide.
Continuous maturation from bone marrow replenishes B cells to ensure adequate immune response even after the plasma cells die.

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Description

This quiz explores the specifics of the adaptive immune response, focusing on the roles of B and T lymphocytes. Learn about VDJ rearrangement and how these cells identify pathogens through unique receptors. Test your understanding of key concepts in immunology.