Humoral Immune Responses II

Question 1

How do T-independent B cells respond to pathogens without T cell help?

Answer 1

Polysaccharides, lipids, and non-protein antigens commonly are polymeric in nature and contain repeating subunits. For this reason, extensive cross-linking activates B cells enough to stimulate proliferation and differentiation.

Question 2

How does number of B cells and antibodies drop following the elimination of infection?

Answer 2

Most differentiated B cells die via apoptosis. Secreted antibodies form immune complexes with residual antigens and so these complexes can interact with B cells via the FcyRIIB receptor which binds Fc tail of IgG antibody and the antigen also binds directly to a non-secreted antibody receptor. The combined signals of Ig and Fc receptor delivers an inhibitory signal.

Question 3

How do antibodies act on infective agents?

Answer 3

They block and neutralize entry of pathogen to sites of action.

They block microbial toxins from binding to receptors.

Extracellular stages of intracellular infection can also be neutralized by antibodies.

(antibodies are most effective if they stimulate production of antibodies)

Question 4

Where are antibodies produced to carry out their actions?

Answer 4

In mucosal secretions

In the blood

Question 5

How long do bone marrow plasma cells function?

Answer 5

For months or years

Question 6

What regions do antibodies use to bind to and block harmful effects from microbes and toxins?

Answer 6

Fab regions

Question 7

What region of phagocytes do antibodies bind?

Answer 7

Fc regions which allow the phagocyte to bind to the heavy chain of the antibodies

Question 8

What are the effector functions of antibodies? (Diagram)

Answer 8

Question 9

Which antibodies are important for opsonization and neutralization of microbes and toxins?

Answer 9

IgG

Question 10

Which antibodies trigger the classical pathway of complement activation?

Answer 10

IgM

Question 11

Which antibodies are important for mucosal immunity?

Answer 11

IgA

Question 12

Which antibodies are important for helminth defense?

Answer 12

IgE

Question 13

How is switching to IgG able to increase half-life of antibodies?

Answer 13

The IgG can be stored and protected from degradation by being internalized in an endosome after binding to an FcRn endosomal receptor and then released when it is needed.

Question 14

What is the function of FcγRI (CD64)?

Answer 14

Phagocytosis activation

Question 15

Where are FCγRI receptors located?

Answer 15

On macrophages, neutrophils, and eosinophils

Question 16

Which Fc receptors have a high affinity for Ig?

Answer 16

FcγRI (CD64)

FCεRI

Question 17

What is the function of FcγRIIA?

Answer 17

Phagocytosis; however, it is inefficient

Question 18

Which Fc receptor is important for feedback inhibition of B cells?

Answer 18

FcγRIIB (it is found on B lymphocytes, DCs, mast cells, neutrophils, and macrophages)

Question 19

What does FcγRIIIA do?

Answer 19

It activates NK cells to produce cytotoxic compounds

Question 20

How does Antibody Dependent Cellular Cytotoxicity take place?

Answer 20

NK cells bind to Fcγ receptor after an antibody has bound to surface of a cell and this results in granule discharge.

This method allows NK cells to dispose of cells that have exposed viral peptides on their surface.

Question 21

What beneficial effect is the FcγRIIB receptor used for?

Answer 21

Pooled IgG from healthy donors can be given to i.v. patients with inflammatory disease (Intravenous Immune Globulin) which can bind to FcγRIIB receptors on various cells reducing inflammation.

Question 22

What receptor do eosinophils and mast cells bind to in order to kill helminth parasties?

Answer 22

IgE antibodies that have coated helminthic parasites are bound at their heavy chains to FcεRI and together with IL-5 (TH2 cells) activate eosinophils which release granule contents that kill worms.

IgE can also bind to mast cells directly and activate their granule release.

Question 23

How do IgA producing B cells localize themselves?

Answer 23

They are predisposed at birth to migrate to mucosal tissue

Question 24

How do IgA antibodies get transported through epithelial layers?

Answer 24

Via carrier proteins that bind to Fc region called Fc poly-IgReceptor (pIgR)

Antibodies are protected from degradation in the gut via vesicles.

When finally on the other side the pIgR is cleaved and IgA is released into the lumen.

Question 25

How do newborns get antibodies from their mother?

Answer 25

Via breast milk which contains IgA antibodies

IgG can also be bound to FcRn on the surface of the gut.