Antibodies Part 2 Flashcards
The variable domain of the heavy chain is broken up into what gene segments?
V, D, J
What are the steps for making a heavy chain?
- the B cell brings a random D segment close to a random J segment, the extra DNA is cut out
- A random V segment is brought close to the DJ combo and the splicing process is repeated
- then the entire unite from the VDJ to the end of the IgD constant region can be transcribed to mRNA
- This primary RNA transcript is alternatively processes using alternative polyA sites and splicing to make only IgM first and then both IgM and IgD
Which polyA tale does the translation machinery stop at first?
the 2nd polyA - this is for secretory IgM
How does the light chain differ in terms of synthesis?
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
Which does the B cell always try first for the light chain: kappa or lambda?
kappa (from one parent and if that one doesn’t work, then the other kappa)
How many Vs are in the heavy chain family?Ds? Js?
65 Vs, 27 Ds and 6 Js
What enzyme does the recombination of antiboyd and T cell receptor DNA?
the RAG recombinases (1 and 2)
When the RAG enzyme complex joins the various V, D and J segments together, it’s somewhat imprecise, leading to what kind of variation?
somatic variation
What are the two basic randomizing mechanisms involved with somatic variation?
- exonucleases can chew away a few nucleotides after the DNA is cut but before the two segments are joined
- Terminal deoxynucleotidyl transferase can add a few nucleotides as well - doesn’t use a template, so it’s additions are random
What is the “price to pay” for somatic variation?
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
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?
receptor editing
What immunoglobulins are expressed on the surfaces of the mature (but inactive) B cells?
IgD and IgM (these are the B cell receptors)
As mature B cells are activated to divide and differentiate, what immunoglobulin do they switch to initially?
secretory IgM
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 ____
DNA, not mRNA
In all cases of class switching, what stays the same and what changes? variable light? constant light? variable heavy? constant heavy?
Everything stays the same except for the constant heavy chain
Why can’t a cell making IgG go back to making IgM?
Because the constant region needed for the IgG was physically removed from the DNA - you can’t get it back
What additional cell is needed for class switching to occur
it requires T cell help
What cytokines from the T helper cells will induce proliferation of the B cells?
IL2, 4, and 5
What cytokines form the T helper cells will induce class switching in the B cells?
IFN gamma forms IgG2s
IL4 makes IgG1 and IgE
Il-5 makes IgE
What’s order of the Igs in order of biggest to smallest?
IgM, IgA (varies), IgE and then IgD and IgG are the same
Why are IgD and IgE typically at such low concentrations in the serum?
Because IgD is only on B cells and IgE is picked up by mast cells and basophils quite quickly
What Ig has the longest half life?
IgG (8-23 days)
What antibody is best for activating complement?
IgM (but also IgG)
What antibody is best for bacterial lysis?
IgM (but also IgG and IgA)
What antibody is best at toxin neutralization?
Tie between IgG and IgA
What antibody is best at antiviral activity?
IgA (but also IgM and IgG)
What antibody is best at mast cell/basophil degraulation?
IgE ONLY!
Why is IgM not very useful at protecting immunocomrpomised individuals?
It’s half life is very short in the serum
Where is IgM present: interstitial fluids of bodily secretions?
present in secretions but not interstitial fluid - too big
What antibody mediates hemolytic disease of the newborn?
IgG
Can IgG be used to protect immunocompromised individuals?
yes
In rheumatoid arthritis, we use IgG as a blocking antibody to block production of what?
TNF
Is IgG more present in the bodily secretions of interstitial fluid?
interstitial fluid
Although IgA’s daily production is greater than any other Ig, why isn’t it the highest in the serum?
Most of it is secreted right out into mucous membranes, so it never really reaches high concentrations in the serum
What antibody is in high concetrnation of breast milk?
IgA
What types of ifnections is IgE particularly important for?
parasitic infections and pulmonary fungal infections
What experiment proved that antigenic specificity is developed BEFORE exposure to antigen?
- injected mice with radioactively labelled antigen X
- 1 week later, inject the with antigen x (no radioactivity) and antigen Y
- 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
The region that’s generated by the
sloppy D/J and V/D joining is called what?
the N region
The recombined V(D)J unit is hypermutable each time a B cell divides after what?
after antigenic stimulation
What is affinity maturation?
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
Can affinity maturation occur for T cells as well?
No
Specifically, how does affinity maturation occur? Like, what’s the enzyme?
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
What are 5 diseases associated with the expression of immunoglobulin genes?
Burkitt's lymphoma acute lymphocytic leuemia acute myelogenous leukemia chronic lymphocytic leukemia chromic myelognous leukemia
