6. B-lymphocytes

Question 1

Where does rearrangement take place?

Answer 1

In the bone marrow

Question 2

What Ig does the immature B-cell express

Answer 2

IgM

Question 3

The mature B-cell leaving the bone marrow expresses.. on its surface

Answer 3

IgG and IgM

Question 4

Negative selection process in the bone marrow

Answer 4

Some B cells express receptors that are autoreactive. These will be eliminated

Question 5

Where does B cells become activated?

Answer 5

In secondary lymphoid organs

Question 6

Receptor editing

Answer 6

If maternal BCR is expressed but recognizes self, cell can silence that gene and express paternal alllele instead

Question 7

Follicular B2 cells

Answer 7

• Develop in secondary lymphoid organs
• Always need a T helper cell for full activation (TD-response)
• Usually protein antigens

Question 8

Marginal zone B2 cells

Answer 8

• Don’t make it to follicle, stay in marginal zone in spleen
• Can mature without help of T helper cells (TI response)
• Usually non-protein antigens

Question 9

B1 B cells

Answer 9

• Non protein antigens (polysaccharides, lipids etc.)

- TI response

Question 10

What initially happens in the paracortical areas of the lymph nodes?

Answer 10

• T cells come into contact with DCs that carry antigen ->DC present antigen and costimulate the T cells found in the lymph node -> T cells differentiate into Th1, Th2, Th17
• B cells starts interacting with antigens -> starts migrating to paracortex

Question 11

Activation of B cell in paracortex

Answer 11

• IgM and IgG receptors cross link
• B cell with antigen from environment will present this on its surface -> If it can interact with Th2 cell -> further activation

Question 12

What happens to the B cells after they’re activated in the paracortex?

Answer 12

• Some can mature immediately to become transient plasma cells -> extrafollicular region
• Some become follicular B cells influenced by follicular T helper cells
• Some migrate to cortex of the lymph node, where T cells secrete cytokines for further maturation of B cells (non plasma cell)

Question 13

Affinity maturation

Answer 13

• Mutations occur during VDJ recombination -> some receptors will be weaker, others will be stronger
• Help from follicular DCs that will present antigens to the developing B cells to see if they bind more strongly or weakly

Question 14

Isotype switch/class switch

Answer 14

• IFNgamma rich area -> will produce IgG
• IL-5 rich area -> IgA produced
• IL-4 / IL-13 -> IgE produced
• If no change in area, IgM will be produced

Question 15

IgA

Answer 15

• Dimer

- Produced by plasma cells situated under mucosal surfaces

Question 16

IgG

Answer 16

• Most important opsonization Ab
• Mediates the antibody-dependent cellular cytotoxicity (ADCC)
• Can cross the placenta

Question 17

IgE

Answer 17

• Helps with ADCC action via eosinophils

- Activation of mast cells

Question 18

CD32

Answer 18

Feedback inhibition of B cells

Fc gamma receptor

Question 19

Localization of B-memory cells

Answer 19

Mantle zone

Question 20

Passive immunization of infants

Answer 20

Through breast milk with IgA

Question 21

Passive immunization of fetus

Answer 21

Transplacental transport with IgG