CAMB 6

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Questions and Answers

What is the process called that removes potentially self-reactive immature lymphocytes?

Clonal expansion

Clonal deletion (correct)

Antibody-mediated clearance

Self-tolerance induction

What mechanism allows B cell survival and differentiation into plasma cells?

Non-self Antigen activation (correct)

T cell activation

Cytokine signaling

Binding of self Antigen

What triggers clonal deletion of self-reactive B cells?

Interaction with T cells

Recognition of self Antigen (correct)

High levels of BCR cross-linking

Recognition of foreign Antigen

After the bone marrow selection process, where do B cells migrate to?

Circulation and lymphatic system Signup and view all the answers

Which of the following is NOT a function of antibodies in the humoral response?

Antigen presentation Signup and view all the answers

What provides Signal 1 for B cell activation?

Binding of Antigen to BCR Signup and view all the answers

Which type of Antigen is associated with IgM production without T cell involvement?

Thymus-independent Antigens Signup and view all the answers

What role does TI-1 Antigen play in B cell activation?

Links to TLRs providing Signal 2 Signup and view all the answers

What role does CD40 play in B cell function?

Induces isotype switching. Signup and view all the answers

What is the significance of activation-induced deaminase (AID) in B cells?

Facilitates isotype switching. Signup and view all the answers

Which immunoglobulin is primarily produced in response to polysaccharide antigens?

IgM Signup and view all the answers

What happens to centrocytes in the germinal center?

Faces apoptosis unless rescued. Signup and view all the answers

Why are MHC class II molecules essential for a T-dependent (TD) B cell response?

They present processed antigens to CD4+ T cells. Signup and view all the answers

What characterizes a centroblast in the germinal center?

It is a rapidly dividing B cell found in the dark zone. Signup and view all the answers

What type of vaccine is a conjugated vaccine?

Links polysaccharide antigens to a protein carrier. Signup and view all the answers

What cytokine is important for the switch to IgE production?

IL-4 Signup and view all the answers

What is a characteristic of T-independent (TI) antigens in pediatric immunization?

They do not require T cell involvement for B cell activation. Signup and view all the answers

What is the first signal that induces B cell activation during a T-dependent response?

The binding of antigen to B cell receptor (BCR). Signup and view all the answers

How does the requirement for polysaccharides to act as T-dependent antigens differ from their T-independent form?

Polysaccharides require a protein conjugate for T-cell activation. Signup and view all the answers

In which part of the lymphatic system do B/CD4+ T cell interactions primarily occur?

Secondary lymphoid organs. Signup and view all the answers

What role does CD40/CD40L binding play in B cell activation?

It provides signal 2 necessary for B cell proliferation. Signup and view all the answers

What happens to B cells that survive the selection processes in the bone marrow?

They migrate into the blood and lymphatics. Signup and view all the answers

Which of the following is true about the activation of B cells with T-dependent antigens?

They require formation of germinal centers for full activation. Signup and view all the answers

What type of antigen allows B cells to present peptides to CD4+ T helper cells?

T-dependent antigens. Signup and view all the answers

What type of antigens can cross-link many BCR molecules on the same B cell surface?

Thymus-independent antigens Signup and view all the answers

What is the primary function of activated dendritic cells in the immune response?

Release cytokine BAFF to enhance antibody production Signup and view all the answers

Which statement accurately describes the development of antibody responses to TI-2 antigens?

They do not develop until after 5 years in humans. Signup and view all the answers

How do B cells require T cells for an effective response to TD antigens?

B cells need T cell cytokines for class switching. Signup and view all the answers

What is a key factor needed for B cells to act as antigen-presenting cells for TD antigens?

Epitopes must be linked either from the same or different molecules Signup and view all the answers

Which vaccine is an example of a conjugate vaccine?

Haemophilus influenzae type b vaccine Signup and view all the answers

What type of antigens generally leads to stronger and more effective antibody responses?

TD antigens Signup and view all the answers

What is required to improve the efficiency of a vaccine against pathogens with TI antigens?

Converting TI antigens to TD antigens Signup and view all the answers

What process leads to the formation of germinal centers (GC)?

B/CD4+ T cell interactions Signup and view all the answers

What characterizes somatic hypermutation in B cells?

High mutation rate of Ig V regions Signup and view all the answers

What happens to centrocytes that fail to bind antigen in the germinal center?

They die by apoptosis or recycle to the dark zone Signup and view all the answers

What is the primary function of follicular dendritic cells (FDC)?

Capture and present intact antigens to centrocytes Signup and view all the answers

What determines the survival of centrocytes in the germinal center?

Higher affinity BCR that binds antigen more effectively Signup and view all the answers

What are follicular T helper cells (Tfh) specialized for?

Providing help to B cells Signup and view all the answers

What is the outcome when a B cell undergoes somatic hypermutation and produces a low-affinity BCR?

It fails to cross-link and cannot present antigen, leading to apoptosis Signup and view all the answers

How do centrocytes signal for survival in the germinal center?

By receiving CD40 signals from Tfh cells after effective antigen binding Signup and view all the answers

Study Notes

B Cell Activation

B cell activation is a crucial part of the humoral immune response.
Immature B cells are removed in the bone marrow if they recognize self antigens through clonal deletion.
Mature B cells move into the blood and lymphatics.
B cell activation requires two signals.
Signal 1 is provided by the binding of antigen to the B cell receptor (BCR).
Signal 1 can be enhanced by complement activation and co-receptor binding.
Signal 2 differs depending on the type of antigen (TI or TD).

Thymus-Independent (TI) Antigens

TI antigens can activate B cells without T cell help.
TI-1 antigens provide signal 2 through binding to other receptors on the B cell surface, like TLRs.
TI-1 antigens can act as polyclonal activators.
TI-2 antigens require extensive cross-linking of BCRs and high concentrations.
Antibody responses to TI-2 antigens develop later in life.

Thymus-Dependent (TD) Antigens

TD antigens require the presence of helper T cells for B cell activation.
B cells internalize TD antigens, process them, and present peptides on MHC class II molecules to CD4+ T cells.
B cells receive signal 2 via CD40/CD40L interaction and cytokines from T cells.
TD antigens lead to a greater antibody response.
TD responses involve antigen processing and presentation by B cells to helper T cells.

Antibody Functions

Neutralization: Antibodies prevent pathogen adherence.
Opsonization: Antibodies promote phagocytosis.
Complement activation: Antibodies activate complement proteins, enhancing opsonization and lysis of certain bacteria.

B/T Cell Interactions and Germinal Centers

B cells present peptide antigens to CD4+ T helper cells in secondary lymphoid organs.
B/T cell interactions occur at the T/B border in lymph nodes and spleen.
Subsequent signalling occurs in germinal centers.
B/T interactions lead to the formation of germinal centers (GC) with the following steps: B cells divide into centroblasts, undergo somatic hypermutation, develop into centrocytes and eventually differentiate into plasma cells or memory cells.

Somatic Hypermutation

Somatic hypermutation introduces point mutations into the variable regions of immunoglobulin genes.
This process increases the affinity of antibodies for their target.
AID (activation-induced cytidine deaminase) is a key enzyme in somatic hypermutation.

Follicular Dendritic Cells (FDCs)

FDCs are specialized cells found in germinal centers.
FDCs present antigens for selection of high-affinity B cells.
They increase the chances of surviving B cells generating the highest affinity antibodies.

Isotype Switching

B cells initially express IgM and IgD.
Isotype switching changes the constant region of antibodies without altering the variable region.
AID is involved in isotype switching.
Different cytokines induce different antibody isotypes (e.g., IgG, IgA, IgE).

Conjugate Vaccines

These vaccines link polysaccharide antigens (which are often TI) to protein carriers, converting the polysaccharide antigens to TD vaccines.
This enhances the immune response.

Follicular T Helper Cells (Tfh)

Tfh cells are a subset of CD4+ T cells specialized in helping B cells.
Tfh cells express CD40L and secrete cytokines.
They are crucial for B cell activation, germinal center formation, and isotype switching.

B Cell Affinity Maturation

Centrocytes with higher affinity BCRs are more likely to survive and differentiate into plasma cells or memory cells.
Lower affinity centrocytes undergo apoptosis.

Antigen Processing and Presentation of Viruses and Bacteria

B cells can process and present virus internal proteins, triggering T cell activation.
Likewise, B cells can process and present epitopes from a bacterial protein, leading to T cell activation.

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Description

Explore the intricate process of B cell activation, vital for the humoral immune response. Learn about the roles of thymus-independent and thymus-dependent antigens in activating B cells and the significance of signaling mechanisms involved. This quiz provides insights into the immune system's functioning and the specifics of B cell responses.