Adaptive immunity 3 - b cells

What cells produce immunoglobulins?

B cells.

What is the secreted form of immunoglobulin called?

Circulating antibodies (Ab).

What is the membrane-bound form of immunoglobulin called?

B cell receptor (BCR).

How many antigen specificities does each B cell produce?

Each B cell produces immunoglobulin with a single specificity.

Where do B cells develop?

In the bone marrow.

What induces differentiation of lymphocyte progenitors into B cells?

Bone marrow stromal cells.

Which immunoglobulins are expressed on immature B cells?

Surface IgM and IgD.

What is central tolerance in B cell development?

Screening immature B cells for autoreactivity before they leave the bone marrow.

What is peripheral tolerance?

Removal of self-reactive B cells that escape the bone marrow.

Where do antibody-producing B cells return to?

The bone marrow.

What generates antibody diversity?

Gene rearrangement of V, D, and J gene segments.

Which gene families are inherited for antibody diversity?

Variable (V), diversity (D), and joining (J) families.

Where does hypervariability occur in TCRs?

In the MHC/peptide-binding region.

How many amino acids are in an immunoglobulin domain?

About 110 amino acids.

What are the two types of light chains?

Kappa (κ) and lambda (λ).

What is the κ:λ light chain ratio in humans?

2:1.

How are heavy chains linked together?

By disulphide bonds.

How is each heavy chain linked to a light chain?

By a disulphide bond.

Are the two heavy chains identical in any given antibody?

Yes.

Are the two light chains identical in any given antibody?

Yes.

How many antigen-binding regions does an antibody have?

Two identical antigen-binding regions.

Where is the variable (V) region located in immunoglobulins?

At the N-terminal end of heavy and light chains.

What determines antigen specificity in antibodies?

The variable region sequence.

What are the hypervariable regions?

HV1, HV2, HV3 (CDR1, CDR2, CDR3).

Which hypervariable region is most variable?

HV3 (CDR3).

What are framework regions?

Areas between hypervariable regions with less variability.

What forms the antigen-binding site?

Paired VH and VL domains with combined hypervariable regions (CDRs).

What is an epitope?

The antigenic determinant recognized by an antibody.

What are conformational epitopes?

Epitopes formed by amino acids brought together during protein folding.

What are linear epitopes?

Epitopes composed of a single continuous amino acid sequence.

What is the Fab region of an antibody?

The variable region that binds antigen.

What is the Fc region of an antibody?

The constant region that binds effector cells or B cell membrane.

What are the two main roles of antibodies?

Specific antigen binding and recruitment of other cells/molecules for pathogen destruction.

What is the function of Fc receptors?

Bind the Fc region of antibodies on effector cells.

Where do T helper cells interact with B cells initially?

Margins of B cell follicles.

Where do B cells move after initial T cell interaction?

Into the germinal centre.

What provides help to B cells in the germinal centre?

T follicular helper (Tfh) cells and follicular dendritic cells.

What is signal 1 in B cell activation?

Antigen binding and cross-linking of membrane immunoglobulin; antigen presentation via MHC II.

What is signal 2 in B cell activation?

CD40–CD40L interaction.

What is signal 3 in B cell activation?

Cytokines produced by T cells.

Where do naïve B cells test their BCRs?

On intact antigen.

What happens to B cells upon activation?

They undergo metabolic reprogramming and extensive transcriptional and epigenetic changes.

What is the role of Tfh cells?

Help B cells proliferate, diversify, class switch, and increase antibody affinity.

Where does somatic hypermutation occur?

In the germinal centre.

What is somatic hypermutation?

Mutation of V region genes during B cell division to alter antibody affinity.

What is the purpose of somatic hypermutation?

To generate higher-affinity antibodies.

What is class/isotype switching?

Changing the antibody constant region (e.g., IgM → IgG, IgA, IgE) while preserving antigen specificity.

What are the two fates of B cells in the germinal centre?

Memory B cells or long-lived plasma cells.

Where do long-lived plasma cells reside?

Mainly in the bone marrow.

How many antibodies can a plasma cell secrete per second?

Thousands.

What is a T-independent response?

An antibody response that does not require T cell help.

What is opsonisation?

Antibody tags pathogens for phagocytosis via Fc receptor binding.

What is complement activation?

Activation of complement proteins by IgM and IgG to destroy pathogens.

What is ADCC?

Antibody-dependent cell-mediated cytotoxicity, where antibodies link target cells to NK cells.

What is agglutination?

Antibodies cross-link epitopes on multiple cells/particles to limit movement and aid clearance.

What is neutralisation?

Antibodies block pathogen binding or toxin activity.

Which antibodies are most effective at agglutination?

IgA and IgM.

Which receptor mediates ADCC for IgG?

CD16 (Fcγ receptor).

What proportion of effector T cells and plasmablasts undergo apoptosis after activation?

Around 90%.

What remains after effector cell apoptosis?

Memory cells providing rapid response upon re-exposure.

What defines immunological memory?

Enhanced frequency and function of memory T cells and rapid reactivation of memory B cells.

What do long-lived plasma cells do?

Continuously produce serum antibodies.

What do memory B cells do upon re-exposure?

Rapidly generate antibody-secreting cells.