B Cells & Antibodies

Question 1

The diversity of both chains of the BCR/antibody comes from…

Answer 1

rearranging gene segments on chromosome 14 (one from mom, one from dad)

Question 2

Four different gene segments for BCRs

Answer 2

V, D, J, and C

Question 3

T or F. Both chromosome 14 works to make a BCR

Answer 3

F! only the chromosome that gets a working combination gets the job! other chromosome shuts down

Question 4

T or F. The Hc is produced first

Answer 4

T!

- process is repeated for Lc and Hc and Lc have to fit together as final test

Question 5

Two interacting components of how a BCR signals

Answer 5

1. pathogen is recognized by epitope (50-79 AAs long) binding to the Hc and Lc ‘antennae’
2. proteins IgA and IgB transmit a signal to let the B cell know to turn on its Ab-making

Question 6

The concept of cross-linking (how the BCR signals)

Answer 6

1. polymeric antigen: repeats of an epitope can bind multiple BCRs and bring them together, also many copies of the same antigen can do this
2. complement receptors on the B cell recognize a fragment of iC3b, enhancing the clustering that occurs with BCRs - amplifies B cell signalling by 100-fold; acts as a co-receptor

Question 7

Second signals for B cell activation

Answer 7

with or without Th help!

Question 8

What is the first signal in B cell activation?

Answer 8

cross-linking or clustering

Question 9

The second or co-stimulatory signal for B cell activation is crucial as it determines the _______ of the B cell response.

Answer 9

quality

Question 10

T cell-dependent activation second signal

Answer 10

CD40 on the B cell binds to CD40L on Th cell AKA CD154

Question 11

T cell-independent activation second signal

Answer 11

involves interaction with a ‘danger signal’, most likely by recognition of PAMPs by Toll-like receptors or other PRRs

Question 12

Advantages of T-independent B cell response

Answer 12

1. fast; don’t need for Th cells to be activated themselves

2. can respond to non-protein antigens

Question 13

Why does the T-independent B cell response need two signals for activation?

Answer 13

the second co-stimulatory signal helps prevent B cells from being activated against polymers from our own bodies like our DNA

Question 14

Third way to stimulate B cells

Answer 14

• mitogens
• can bind to molecules on B cells that happen to be associated with BCRs = clustering!
• clustering occurs independent of any antigen recognition by the BCR = activation of many B cells = polyclonal = many clones of B cells are activated this way
• not what we want! some parasites use this to confuse our immune system

Question 15

Maturation of B cells

Answer 15

1. class switching
2. somatic hypermutation
3. career decision

Question 16

when genes for the BCR undergo mutations that increase the affinity of the BCR for its cognate antigen

Answer 16

somatic hypermutation

Question 17

cutting and pasting Hc genes on chromosome 14 leads to changes in …

Answer 17

antibody class

Question 18

Like five IgG structures held together by a J chain

Answer 18

IgM

Question 19

This antibody is very good at activating the complement classical pathway

Answer 19

IgM

• does this by allowing two C1qrs protein complexes to come together via its Fc region when IgM binds to its cognate antigen on an invader
• the C1s lose their inhibitor molecule which leads to activation of a C3 convertase

Question 20

This antibody class is a good neutralizer and can cross the placenta and protect a fetus

Answer 20

IgG

Question 21

Half life of IgM vs IgG

Answer 21

one day vs three weeks

Question 22

The most abundant class of antibody in the blood

Answer 22

IgG

Question 23

Subclasses of IgG

Answer 23

• IgG3 fixes complement well, and can be recognized by NK cells (ADCC
• IgG1 is a great opsonizer and cna enhance phagocytosis

Question 24

Most abundant antibody of all

Answer 24

IgA

- rare in blood but very common on mucosal surfaces and in mucosal secretions

Question 25

IgA structure

Answer 25

like two IgGs held together by a clip protein

• clip is a ‘passport’ for secretion into gut
• also a good neutralizer and found in breast milk

Question 26

T or F. IgA activates complement and can opsonize

Answer 26

Doesn’t activate complement and doesn’t opsonize

- Bc otherwise our mucosal membranes will be inflamed all the time!

Question 27

T or F. Mast cells can also phagocytose opsonized bacteria and signal neutrophils to migrate to an infection

Answer 27

T

Question 28

Allergies are caused by

Answer 28

mast cells degranulating

• IgE attaches to mast cells Fc receptors after first exposure
• upon next exposure to allergen, mast cells degranulate releasing histamine, etc.

Question 29

Class switching is controlled by…

Answer 29

cytokines produced by Th cells

Question 30

a uniquely high rate of mutation (1000x normal rate) in the V, D, and J region genes after class switching has taken place

Answer 30

somatic hypermutation

- affects Fab region of Ab

Question 31

B cell that continues to secrete Ab after migrating to spleen or bone marrow

Answer 31

plasma cell

Question 32

This only occurs with T-dependent antigens and Th help

Answer 32

Memory B cells