B-cell Activation

Question 1

What are the 3 signals that B-cells require for activation?

Answer 1

1. The binding of a B-cell to its antigen
2. The binding of the B-cell coreceptor to the complement factor C3d
3. Linked antigen recognition by a follicular helper T-cell (CD40) which induces B-cell proliferation

Question 2

What is the process and reason behind the conjugate pair of a B-cell and follicular helper T-cell?

Answer 2

The T-fh cell recognizes a peptide a peptide linked to the B-cell, CD40 and cytokines drive B-cell proliferation (delivered through a synapse)

Question 3

What is the boundary region?

Answer 3

The area in lymphatic tissue where the B-cell and T-cells can intermingle and have some contact

Question 4

In what ways do B-cells differentiate into plasma cells?

Answer 4

1st: The B-cell, T-cell conjugate pair moves to the medullary cord, these sometimes differentiate into low affinity IgM secretion plasma cells
2nd: Some B-cells will return to the follicles to form a germinal center, which results in somatic hypermutation and class switching.

Question 5

What is the dark zone in germinal centers?

Answer 5

Contains centroblasts, which are rapidly proliferating B-cells undergoing hypermutation (currently low-affinity)

Question 6

What does the light zone in germinal centers contain?

Answer 6

Centrocytes, which display the mutated B-cell receptors, testing them out, there are also a high concentration of FDC’s and T-fh cells here in the light zone

Question 7

What determines how B-cells class swich?

Answer 7

Cytokines as well as the interactions between the CD40 (B-cell) and CD40L (T-cell)

Question 8

What are Thymus Independent immune responses?

Answer 8

Some antigens do not require thymus-produced B-cells, which do not require T-cell help (common with bacterial antigens)

Question 9

What type of B-cell does TI-1 antigen activate in high concentration?

Answer 9

Polyclonal B-cells

Question 10

What are TI-2 antigens?

Answer 10

These antigens have highly repetitive structures like capsular polysaccharides, these activate the innate-like B1 cells

Question 11

What are the characteristics of IgM antibodies?

Answer 11

Low affinity (produced before hypermutation), form pentamers to increase the overall binding strength, activates the complement system

Question 12

What are the subclasses and general function of IgG antibodies?

Answer 12

IgG is the most abundant antibody in the blood, and operates in monomers.
IgG is a great all-around antibody
All four subclasses of IgG differ in the hinge region of the antibody structure
IgG1, IgG2, IgG3, IgG4

Question 13

Which antibodies circulate in the blood?

Answer 13

monomeric IgA, IgG, and IgM

Question 14

Which antibody primarily protects mucosal surfaces?

Answer 14

Dimeric IgA- there is a lot of SA, so there is a lot of dimeric IgA present in the body

Question 15

How is dimeric IgA primarily obtained?

Answer 15

Through breastmilk

Question 16

What do high affinity neutralizing antibodies do?

Answer 16

Prevent organisms and toxins from binding to host cells- preventative measure (IgG and IgA)

Question 17

Which antibodies activate the classical complement pathway?

Answer 17

IgM, IgG1, and IgG3 will recruit C1, activating the classical complement pathway

Question 18

What function do IgE antibodies serve?

Answer 18

These bind to mast cells, eosinophils, and basophils to serve as protection against parasites and type 1 hypersensitivity reactions

Question 19

What drives the promotion of antibody-dependent cell-mediated cytotoxicity?

Answer 19

The binding of IgG to to Fc gamma receptors on natural killer cells, this promotes phagocytosis

Question 20

What are the symptoms and pathology of XLA?

Answer 20

There is defective B-cell receptor signaling, and thus no functional B-cells as a result
symptoms: susceptible to bacterial and fungal infections

Question 21

What are the symptoms and pathology of hyper IgM deficiencies?

Answer 21

Individual only produces low affinity IgM antibodies
CD40L deficiency
symptoms: susceptible to bacterial and fungal infections