B Cells + Antibodies

Question 1

Antibodies are composed of

Answer 1

Two identical heavy chains
has one variable site Vh and three constant sections (Ch1, Ch2, Ch3)
two identical light chains
has one variable site Vl and one constant domain Cl

Question 2

Fab Site

Answer 2

Complex composed of Vl and Cl from light chain and Vh and Ch1 from heavy chain

Question 3

Fas Site

Answer 3

Complex composed of Ch2, Ch3 from heavy chains

Also known as the effector region

Question 4

What is different about IgM and IgE heavy chain?

Answer 4

IgM and IgE have Ch4

4th constant domain on their Heavy Chain

Question 5

How do antibodies on B cells become activated

Answer 5

Antibodies on B Cells need to cross link with antigen in order to become activated

Question 6

Within each variable domain, there are ______ regions of ________

Answer 6

There are three regions of hypervariablity
These regions (Variable Light Vl, and Variable Heavy Vh) can bind with antigen creating 6 sites for antigen interaction

Question 7

Difference between isotypes and idiotypes

Answer 7

Isotypes are classified by the constant regions of the antibody i.e. Cl and Ch1, Ch2, Ch3 (+Ch4 if IgM or IgE)
Antibodies that bind to Fc region are good ways to identify different isotypes

Idiotype: variable regions of heavy and light chains
i.e. comining sites of Vl and Vh
Idiotypes demonstrate the specific clonal amplification of antibodies

Question 8

IgM

Answer 8

membrane receptor on B-cell
can be synthesized and secreted as pentamer
Pentamer of IgM is held together by J chain
Potent activator of complement

Question 9

Immature B cells are marked with _____ and express ______ and ______ when they are fully mature

Answer 9

Immature B cells express IgM
Mature B Cells express both IgM and IgD
IgD is the maturation factor of IgD

Question 10

IgD

Answer 10

Cannot be secreted

Question 11

IgG

Answer 11

highest in serum content
has longest 1/2 life
Complement activator
Monmer that is less efficient than IgM
Great opsonizer
IgG can cross the placenta

Question 12

When does Macrophage bind to IgG?

Answer 12

Macrophages only bind to Fc portion of IgG after IgG has bound to rorereign substance
Phagocytic cells have FcGamma receptors that accept IgG Fc portion

Question 13

IgA

Answer 13

involved in mucosal immunity
relatively mild antibody
blocks bacteria from replicating
relies on peristalic action to then clear bacteria and pathogens
IgA is a dimer held together by J chain
IgA prevents damage to epithelia cells in the gut

Question 14

IgE

Answer 14

sensatizes mast cells, basophills and eosinophills
x-link of IgE causes mast cells to secrete granules of histamines and other contents
IgE works with PARASITES
IgE DOES NOT need to bind to antigen before binding to Fc(epsilon) receptor
i.e. IgE can bind directly to Fc(epsilon) receptor

Question 15

Cross Reactivity and Example

Answer 15

Cross reactivity is generating antibodies to one substance. That same antibody can then react with another completely different substance

i.e. we generate antibodies to the terminal sugars of bacteria in our gut flora. These same antibodies react with the different antigens found on blood types

Question 16

T Cells mainly react with ______ moiety while B cells can react with _____ moiety

Answer 16

T cells mainly see polypeptide of bacteria
B Cells can react with carbohydrate moiety of pathogen
NB: T cells with peptide moiety can than activate B Cells

Question 17

Ig stages and gene expression

Answer 17

Stems Cells: germ line configuration (naive)
Pro-B Cells: D/J begins
Pre-B Cell: VDJ rearangement is complete in cytoplasm but no light chain. VDJ chain is called (u [mew]-heavy chain)
Immature B Cell: VDJ and VJ is complete

Question 18

Genomic Makeup of Heavy Chain

Answer 18

Beginning
100 V segments (Vh1, Vh2, …, Vh100)
27 D Segments (D1, D2, …, D27)
6 J segments (Jh1, Jh2, …, Jh6)

NB: Only Heavy Chain had D section, so expression of Dh1 is not necessary

Question 19

1st step of Heavy Chain Rearrangement

Answer 19

DJ rearrangement
one D section merges with one J section i.e. D3 and Jh2
Circular DNA segment between two portions gets removed
Circular excess DNA is called episome

Question 20

2nd Step of Heavy Chain Rearrangement

Answer 20

VD rearrangement

Question 21

Hallmark of Pre B Cell

Answer 21

VDJ rearangement is complete
mew-heavy chain is in cytoplasm bound to surrogate light chain
mew heavy chain and surrogate light chain are transported to the surface of the cell.
Transport indicates to stop production of heavy chain and switch over to production of light chain

Question 22

Enzyme that facilitates recombination of heavy chain

Answer 22

VDJ recombinase

i.e. RAG 1 and RAG 2 are lymphoid specific DNA recombination enzymes

Question 23

Two isotypes of light chain are _____ and ______

Answer 23

kappa and lambda

Kappa light chain has no D gene segment

Question 24

Each antibody receptor has a unique _________ (isotype or idiotype)?

Answer 24

Idiotype

Isotype is coded for by constant domain and is a family of antibodies

Question 25

Diff between Primary transcript, mRNA and protein

Answer 25

Primary Transcript includes portion of V segment and J segment that will be cut out via transcription start site and alternative splicing
i.e. Vh1-Vh2-D3-Jh4-Jh5-Jh6-u1-u2-u3-u4
Vh1 will get removed by choosing a transcription site just before Vh2 and Jh5 and Jh6 will get removed by alternative splicing

mRNA include just what you want and protein is functional antibody.

Question 26

12 / 23 spacer rule for heavy chain

Answer 26

Certain DNA elements that control recombination process
Rearrangement is only allowed to occur between a spacer of 12 and 23
[Vh] 7 – 23 – 9 ——9 – 12 – 7 [DElement] 7 – 12 – 9 —— 9 – 23 – 7 – [JElement]

Question 27

12 / 23 rule for lambda and kappa chain

Answer 27

[Vlambda]-7- 23 - 9 ——9- 12- [Jlamda]

[Vkappa]-7- 12 - 9 ——9- 23- [Jkappa]

Question 28

Generating Idiotype Diversity

Answer 28

1. Multiple V regions
2. Recombination of VJ (light) and VDJ (heavy)
3. Heavy and light combinations
4. VDJ recombination is not perfect
   Gives rise to junctional diversity
   i.e. add/subtract 1 nucleotide between V and D segment
5. Somatic hypermutation

Question 29

Principle Enzyme of imperfect VDJ rearrangment

Answer 29

Terminal Deoxynucleotidyl transferase (TDNT)

heavy chain only

Question 30

Somatic hypermutation only occurs in _____ cells

Principle enzyme of somatic hypermutation

Answer 30

B Cells

Activation-Induced cytomine deaminase (AID)