B cells

What are the main components of the B cell receptor (BCR)?

CD79A, CD79B, and an immunoglobulin.

How does B cell receptor activation occur?

Antigen binding and cross-linking of two receptors exposes ITAMs on CD79A, leading to B cell activation.

Do B cells require antigen-presenting cells for antigen binding?

No, BCRs bind intact antigens without the need for APCs.

What happens after B cell activation?

They undergo clonal selection, proliferation, and differentiation into antibody-secreting cells; all progeny share the same antigen-binding specificity.

What is T cell-independent B cell activation?

Activation by simple repeating polymers; results in short-lived replication, low-level IgM secretion, migration to cortex/paracortex interface, and no memory cell formation.

What is a primed B cell?

A B cell that has phagocytosed an antigen, processed it, and presented a linear peptide on MHC-II for T cell interaction.

What happens when a primed B cell interacts with a helper T cell?

Mutual activation via cytokines (IL-2, IL-4, IL-5), leading to isotype switching, affinity maturation, plasma cell differentiation, migration out of germinal centers, and memory cell formation.

Which cytokines are involved in B cell-T cell interactions?

IL-2, IL-4, IL-5.

Which immunoglobulin isotypes can B cells secrete?

IgM, IgE, IgG, IgA.

Which immunoglobulin is only a receptor?

IgD.

What determines antibody isotype?

The structure of the heavy chain constant region.

Which isotype is secreted first by B cells?

IgM.

Where does isotype switching occur, and what does it require?

In peripheral lymphoid organs; cytokine-dependent and requires T cell help.

What is the difference between T-dependent and T-independent B cell activation?

T-dependent: requires helper T cell, leads to isotype switching, memory formation. T-independent: no T cell help, only IgM produced, short-lived, no memory.

What is the difference in antigen recognition between B cells and T cells?

B cells recognize intact antigens; T cells recognize processed peptides presented on MHC.

Which receptors on macrophages and monocytes mediate clearance of IgG-opsonized microbes?

Fc receptors for the Fc region of IgG.

How are antibody quantities measured in plasma?

Mass concentration in grams per deciliter.

What is an antibody titer?

The highest dilution of serum that still gives a positive reaction for antigen binding.

What does an antibody mass concentration measure?

Total quantity of antibodies in plasma.

What does an antibody titer measure?

Antigen-specific antibody activity in a sample.