Antibodies Part 2

Question 1

The variable domain of the heavy chain is broken up into what gene segments?

Answer 1

V, D, J

Question 2

What are the steps for making a heavy chain?

Answer 2

1. the B cell brings a random D segment close to a random J segment, the extra DNA is cut out
2. A random V segment is brought close to the DJ combo and the splicing process is repeated
3. then the entire unite from the VDJ to the end of the IgD constant region can be transcribed to mRNA
4. This primary RNA transcript is alternatively processes using alternative polyA sites and splicing to make only IgM first and then both IgM and IgD

Question 3

Which polyA tale does the translation machinery stop at first?

Answer 3

the 2nd polyA - this is for secretory IgM

Question 4

How does the light chain differ in terms of synthesis?

Answer 4

It’s very similar to the heavy chain, but it only has a V and J segment (no D) an donly one constant domain gene instead of 3

Question 5

Which does the B cell always try first for the light chain: kappa or lambda?

Answer 5

kappa (from one parent and if that one doesn’t work, then the other kappa)

Question 6

How many Vs are in the heavy chain family?Ds? Js?

Answer 6

65 Vs, 27 Ds and 6 Js

Question 7

What enzyme does the recombination of antiboyd and T cell receptor DNA?

Answer 7

the RAG recombinases (1 and 2)

Question 8

When the RAG enzyme complex joins the various V, D and J segments together, it’s somewhat imprecise, leading to what kind of variation?

Answer 8

somatic variation

Question 9

What are the two basic randomizing mechanisms involved with somatic variation?

Answer 9

1. exonucleases can chew away a few nucleotides after the DNA is cut but before the two segments are joined
2. Terminal deoxynucleotidyl transferase can add a few nucleotides as well - doesn’t use a template, so it’s additions are random

Question 10

What is the “price to pay” for somatic variation?

Answer 10

Remember that it’s randomly taking out and adding nucleotides, so 2/3 times, it will cause a frame shift mutation, which will terminate transcription. When this happens, the B cell responsible for it tries the other allele, but if that one doesn’t work either, the cell will be weeded out of the system

Question 11

Sometimes though, if recombination results in a faulty gene but the RAG recombinases are still active, they’ll just try again. What’s this called?

Answer 11

receptor editing

Question 12

What immunoglobulins are expressed on the surfaces of the mature (but inactive) B cells?

Answer 12

IgD and IgM (these are the B cell receptors)

Question 13

As mature B cells are activated to divide and differentiate, what immunoglobulin do they switch to initially?

Answer 13

secretory IgM

Question 14

As B cells continue to differentiate, they may undergo additional class switching to IgG or IgE or IgA. Unlike the previous class switching, this occurs at the level of rearrangements of ____

Answer 14

DNA, not mRNA

Question 15

In all cases of class switching, what stays the same and what changes? variable light? constant light? variable heavy? constant heavy?

Answer 15

Everything stays the same except for the constant heavy chain

Question 16

Why can’t a cell making IgG go back to making IgM?

Answer 16

Because the constant region needed for the IgG was physically removed from the DNA - you can’t get it back

Question 17

What additional cell is needed for class switching to occur

Answer 17

it requires T cell help

Question 18

What cytokines from the T helper cells will induce proliferation of the B cells?

Answer 18

IL2, 4, and 5

Question 19

What cytokines form the T helper cells will induce class switching in the B cells?

Answer 19

IFN gamma forms IgG2s
IL4 makes IgG1 and IgE
Il-5 makes IgE

Question 20

What’s order of the Igs in order of biggest to smallest?

Answer 20

IgM, IgA (varies), IgE and then IgD and IgG are the same

Question 21

Why are IgD and IgE typically at such low concentrations in the serum?

Answer 21

Because IgD is only on B cells and IgE is picked up by mast cells and basophils quite quickly

Question 22

What Ig has the longest half life?

Answer 22

IgG (8-23 days)

Question 23

What antibody is best for activating complement?

Answer 23

IgM (but also IgG)

Question 24

What antibody is best for bacterial lysis?

Answer 24

IgM (but also IgG and IgA)

Question 25

What antibody is best at toxin neutralization?

Answer 25

Tie between IgG and IgA

Question 26

What antibody is best at antiviral activity?

Answer 26

IgA (but also IgM and IgG)

Question 27

What antibody is best at mast cell/basophil degraulation?

Answer 27

IgE ONLY!

Question 28

Why is IgM not very useful at protecting immunocomrpomised individuals?

Answer 28

It’s half life is very short in the serum

Question 29

Where is IgM present: interstitial fluids of bodily secretions?

Answer 29

present in secretions but not interstitial fluid - too big

Question 30

What antibody mediates hemolytic disease of the newborn?

Answer 30

IgG

Question 31

Can IgG be used to protect immunocompromised individuals?

Answer 31

yes

Question 32

In rheumatoid arthritis, we use IgG as a blocking antibody to block production of what?

Answer 32

TNF

Question 33

Is IgG more present in the bodily secretions of interstitial fluid?

Answer 33

interstitial fluid

Question 34

Although IgA’s daily production is greater than any other Ig, why isn’t it the highest in the serum?

Answer 34

Most of it is secreted right out into mucous membranes, so it never really reaches high concentrations in the serum

Question 35

What antibody is in high concetrnation of breast milk?

Answer 35

IgA

Question 36

What types of ifnections is IgE particularly important for?

Answer 36

parasitic infections and pulmonary fungal infections

Question 37

What experiment proved that antigenic specificity is developed BEFORE exposure to antigen?

Answer 37

1. injected mice with radioactively labelled antigen X
2. 1 week later, inject the with antigen x (no radioactivity) and antigen Y
3. mice got sick to antigen x, but not to antigen y

This showed that they weren’t able to develop antibody against x because it killed all the b cells that had specificity for it

Question 38

The region that’s generated by the

sloppy D/J and V/D joining is called what?

Answer 38

the N region

Question 39

The recombined V(D)J unit is hypermutable each time a B cell divides after what?

Answer 39

after antigenic stimulation

Question 40

What is affinity maturation?

Answer 40

It’s because of the hypermutable nature after antigenic stimulation… There is a good chance that one of the duaghter cells will make a slightly different antibody, and over time you’ll have selection of the best fitting mutants after antigenic stimulation to allow for a gradual increase in affinity during an immune response

Question 41

Can affinity maturation occur for T cells as well?

Answer 41

No

Question 42

Specifically, how does affinity maturation occur? Like, what’s the enzyme?

Answer 42

Activation-induced (cytidine) deaminase purposely converts random cytoskines in the CDR gene region to uracil, so you get guanine mismatch which is then excised and filled in with something else - creating mutations

Question 43

What are 5 diseases associated with the expression of immunoglobulin genes?

Answer 43

Burkitt's lymphoma
acute lymphocytic leuemia
acute myelogenous leukemia
chronic lymphocytic leukemia
chromic myelognous leukemia