Humoral Immunity

Question 1

B cell receptors are ____.

Answer 1

Antibodies

Question 2

Which type of antibody is MOST important?

Answer 2

IgG - has the broadest functions

Question 3

The first antibody active in the adaptive immune response is…

Answer 3

IgM

Question 4

All mature B cells display ____ on their cell surfaces.

Answer 4

Antibodies

Question 5

When activated, B cells can differentiate into ____ which secrete soluble ____.

Answer 5

When activated, B cells can differentiate into PLASMA CELLS which secrete soluble ANTIBODIES.

Question 6

What are the three main functions of antibodies?

Answer 6

1) Neutralization of the pathogen and its toxins
2) Opsonization - tagging of bacteria for phagocytosis
3) Activation of complement - via classical pathway, whereby C1 binds to Ab-coated pathogens
Bonus: ADCC (NK cells and eosiniphils)

Question 7

What is antibody-dependent cell-mediated cytotoxicity (ADCC)?

Answer 7

• Facilitates NK response to viruses
• Also facilitates eosinophil response to parasites
• When Abs bind to the pathogen, immune cells recognize the Ab
• This cross-linking signals for the immune cell to attack the pathogen

Question 8

Describe the structure of antibodies.

Answer 8

• 2 heavy chains and 2 light chains
• Heavy chain is the constant region and determines the class/isotype
• Both heavy and light chains form the variable region, which determines the antigen binding site

Question 9

Diversity of antibodies and the variable region is achieved via…

Answer 9

Somatic recombination (VDJ rearrangement)

Question 10

Immature B cells display ___ antibodies on their surfaces.

Answer 10

IgM & IgD

Question 11

Junctional diversity is generated by the addition or deletion of ____ during somatic recombination.

Answer 11

Single nucleotides

Question 12

What is affinity maturation?

Answer 12

• Also called somatic hypermutation
• Occurs AFTER B cell activation by antigen
• Clones will have point mutations in the antibody V-region genes - this variability could allow for some clones with increased affinity for the antigen

Question 13

What is isotype class switching?

Answer 13

After B cell activation, the heavy chain of antibodies can change to allow for class switching

Question 14

The first antibodies to be secreted by plasma cells are…

Answer 14

IgM

Question 15

AID is an enzyme that assists with…

Answer 15

Somatic hypermutation and isotype class switching

Question 16

What are three requirements for B cell activation?

Answer 16

1) Encounter the specific antigen that will bind the antibody (BCR)
2) CD40L on T cells binds to CD40 on B cells
3) Activation from cytokines produced by T cells

Question 17

Do B cells ALWAYS need T cells to become activated?

Answer 17

No - some antigens are capable of initiating an antibody response independent of T cells

Question 18

How do B cells find their corresponding T cells?

Answer 18

• B cells can endocytose pathogens and load peptides onto MHC molecules
• Peptide-MHC complexes on the B cell surface
• T cells that recognize and bind to the specific peptide-MHC complex will release cytokines and bind to CD40 via CD40L to activate the B cell

Question 19

Describe central and peripheral tolerance.

Answer 19

During B cell development, B cells are tested for autoreactivity before they leave the bone marrow (central tolerance) and again in the periphery (peripheral tolerance).