CH 9-Immunity mediated by b cells & antibodies

B-cells become activated when their-

-receptors are cross-linked by antigens

What are the signal transduction proteins which activate B cells after the initial antigen binding to a naïve B cell?

IG-(alpha) IG-(beta)

Functional BCR (B cell receptors)

Iga and Igb and IgM

B cell co-receptor is composed of three proteins:

CD 19, CR2 (CD21), CD81

CD 19

Signal protein for receptor

CR2/ CD21

the receptor protein for complement C3 fragments (iC3b, C3d)

CD 81

thought to be involved in signal transduction

B cell activation does not  require T cell signals in response to certain antigens. They are thymus independent antigens (TI). (T/F)

True

TI-1 antigens can’t activate B cells without any signals from T helper cells. EX, LPS antigen (T/F)

False

internalized pathogens can activate Toll-like receptors (TLRs) in B cells, leading to B cell activation and only IgM production. (T/F)

True

With IgM being produced, isotype switching is not dependent on cytokine signals from T cells (T/F)

False

CD40 proteins-

-are the cell membrane proteins that coordinate the development of cognate pairs of T/B cells

IL-4

the primary signal for B cell differentiation into a plasma cell following clonal expansion

Dendritic cells that serve as APCS for B cells

• develop from stromal cells in connective tissue

Dendritic cells that serve as APCS for T cells

• develop from myeloid stem cells in the bone marrow

CD40 receptor is on the:

B-cell

CD40 ligand is on the:

T-cell

Cytokines (mainly IL-4) from the T-cell stimulate-

-clonal expansion in thymus dependent antigens.

What are the cells that undergo somatic hypermutation/isotope switching?

• B cells that divide in lymph node medulla and produce IgM antibodies

• also, some that migrate w/ their own cognate T cells to cortex of lymph node-forming germinal centers

Adhesion molecules keep B-cells in the lymph node. (T/F)

True

Centroblasts

• B-cells that undergo class switching and somatic hypermutation- enlarge and divide

• T helper cells divide around the periphery of the germinal center

primary nodule has-

-naïve B cells.

secondary nodule is a site with-

-a germinal center (centroblasts, or B cells undergoing class switching).

swelling of lymph nodes in an infection is due to the growth of this

Germinal Centers

The mantle zone is the area-

-around the nodules that allows flow of naïve B cells

Affinity Maturation

• screened in the lymph node for high-affinity binding to antigen

• Cytokines from the T cells signal B-cell survival if high-affinity antibodies are produced

Plasma cell development is controlled by-

-BLIMP-1 transcription factor ( signals for this include the IL-10 ).

• increase immunoglobulin protein synthesis, while blocking cell proliferation and further hypermutation

Once a B cell has differentiated into a plasma cell, it does not produce only Ig (T/F)

False

IL-10 signals for-

-plasma cell differentiation.

IL-4 signals for -

-memory cell differentiation.

transcytosis

transport antibodies (IgA, IgG, IgM), across their interior, from one side to the other

IgE

• mainly in skin and mucosal membrane connective tissues-histamine

• also internal parasites

IgA

(dimeric) in secretions, in blood

IgM

1st soluble antibody, pentamer, in blood

IgG

most abundant, secondary immune reponse- memory cells (in blood)

Opsonization

where immune proteins (opsonins) coat pathogens, making them more easily recognized and destroyed by phagocytic cells

Neutralization

• prevents cellular infections

• where antibodies bind to and inactivate pathogens, such as viruses or bacteria, rendering them harmless.

Secreted dimeric IgA can inhibit binding of bacteria to epithelial cells in the respiratory tract. (T/F)

True

Toxoids are-

-modified toxins, altered to remove its toxicity (good for vaccines).

Lack of C4A is associated with-

-SLE (systemic lupus erythematosus).

Antigen-dependent cell-mediated cytotoxicity (ADCC)

a mechanism for destroying body cells infected by a virus or turned cancerous