L6 Humoral Immunity

Question 1

Simplified humoral response pathway

Answer 1

Antigen recognition
Activation of B-lymph
Proliferation
Differentiation
Plasma cells (antibody secretion), IgG (Isotype switching), High affinity IgG (Affinity maturation, Memory b cells)

Question 2

B cell receptor (BCR)

Answer 2

Membrane bound immunoglobulin (IgM/IgD) with a unique specificity Surface single antibody molecule associated Igα and Igβ chains (signal transduction)

Question 3

Two roles in B cell activation:

Answer 3

• Preforms first signal of activation when it binds to cognate antigen
• Internalise antigen to be processed so peptides can be presented on MHC II molecules

Question 4

Distinct feature of B-cells

Answer 4

• Tail and associated molecules to transduce signals
• a heavy and light chain

Question 5

Same feature of B-cells and T-cells

Answer 5

Constant and variable regions

Question 6

What happens to the constant region during class switching

Answer 6

It stays the same :)

Question 7

Antibody (immunoglobulin) structure

Answer 7

• 4 polypeptide chains: : two identical heavy (H) chains and two identical light (L) chains— with each chain containing a variable region and a constant region
• Each variable region of the heavy chain (VH ) or of the light chain (VL ) contains three hypervariable regions.
  Fab - fragment, antigen-binding region
  Fc – fragment, crystalline
  ▪ There are 5 classes: IgM, IgD, IgG, IgA and IgE

Question 8

Name the 5 classes of B-cell antibodies

Answer 8

IgM, IgD, IgG, IgA and IgE

GAMED MEGAD DEMAG

Question 9

Gene rearrangement and BCR diversity

Answer 9

▪ A random variable region gene segments is selected and joined to a downstream DNA segment
▪ This process in the bone marrow is independent of presence of antigens

Question 10

Do B-cells go through central or peripheral tolerance

Answer 10

Both, self-reactive cells become anergic (functionally unresponsive) or die by apoptosis

Question 11

What happens to B-cells that self-recognise

Answer 11

Immature B lymphocytes that recognise self-antigens in the bone marrow with high affinity either change their specificity (receptor editing) or are deleted

Question 12

Where does the development from immature into mature B cells occur?

Answer 12

within secondary lymphoid tissues

Question 13

B-cell activation 2 ways

Answer 13

T-independent and T-dependent

Question 14

T-independent antigens

Answer 14

Nonprotein antigens like polysaccharides and carbohydrates and lipids can activate B-cells

Question 15

T-dependent antigens

Answer 15

Protein antigens

Question 16

Antibodies that are made through protein antigens typically show what

Answer 16

Isotype switching and are of high affinity

Question 17

What happens if activated B cells encounter specific signalling molecules through their CD40 and cytokine receptors

Answer 17

(both modulated by T helper cells), they undergo antibody class switching to produce IgG, IgA or IgE antibodies that have defined roles in the immune system.

Question 18

isotype:

Answer 18

Antibodies can come in different varieties known as isotypes, which refer to the genetic variations or differences in the constant regions of the heavy and light chains of the antibody.

Question 19

class switch recombination:

Answer 19

A biological mechanism that changes a B cell’s production of antibodies from one class to another; for example, from an isotype called IgM to an isotype called IgG.

Question 20

The type of antigens that T-independent B-cells produce

Answer 20

• Mainly IgM
• Low affinity
• short lived plasma cells

Question 21

The type of antigens that T-dependent B-cells produce

Answer 21

• Isotype switched
• High affinity
• Memory B cells
• Long lived plasma cells

Question 22

T-independent antigens and antibodies

Answer 22

▪ Antigens are multivalent (e.g., bacterial polysaccharides)
▪ Responses are fast (1-2 days) and predominantly IgM, with low affinity
▪ Short-lived plasma cells
▪ Weak in infants and young children

Question 23

T-dependent antigens and antibodies

Answer 23

▪ Antigens must contain a protein component
▪ B cell receives two signals: (i) through its antigen receptor and (ii) through interaction with T-helper cell that recognises degraded fragments of the same antigens
▪ Responses are slower (several days), and all immunoglobulin isotypes are produced and have high-affinity
▪ Memory B cells and long-lived plasma cells

Question 24

B cell activation by helper T cell and germinal center reaction

Answer 24

▪ Activated CD4 T cells and B cells migrate toward one another and interact at the edges of the follicles, where the initial antibody response develops
▪ Some of the cells migrate back into follicles to form germinal center, where the more specialised antibody responses are induced
▪ The meeting of the two cells is called linked recognition

Question 25

Linked recognition –

Answer 25

B and T cells see the same parts of the same antigen, requires precise regulation of the migration of activated B and T cells into specific locations