2 B cell development Flashcards
what areas make up the antibody binding sites?
the Fab region which is made up of the light and heavy chains.
what does it mean to be in the germline form when talking about B cells?
It means that the structures (chains) have not yet been rearranged.
T/F Unrearranged genes can express heavy or light chain proteins?
False, only rearranged genes can express these.
what 4 gene segments make up the functional antibody genome?
The V, D, J and C regions.
what are the different forms of the light chain called? The heavy chain?
Kappa and Lambda.
Heavy chain is just called heavy chain.
which parts make up the heavy chain?
V, D, J and C regions.
what is combinatorial diversity?
the diversification of antibody by using random choices of V, D, and J regions to make the Fab.
what does a joint sequence do to antibody specificity?
They help to diversify the antibody. (adds sequences between V, D, and J regions)
what is junctional diversity?
diversification of antibody coding sequences due to the sequences created between the V, D and J regions.
what 2 things specifically dictate antibody specificity?
Combinatorial and junctional diversity
what is a CDR?
complementarity determining region. They are used to directly bind the antigen (CDR1-3) and are found on the heavy and light N terminus.
The combined effect of combinatorial and junctional diversity is predicted to produce how many different antibody specificities?
more than 1 x 10^11
what is NHEJ?
Non homologous end joining
Where do you find RAG 1 and 2?
only expressed in developing B and T cells.
what does RAG bind?
RSS 12 or 23 Bp areas
What does TdT do?
adds nucleotides to the end of DNA breaks without a template.
what do KU 70 & 80 do?
bind ends of broken DNA and recruit others.
What does DNA PK do?
Serine/threonine phosphokinase that recruits Artemis and is required for DNA repair.
What does artemis do?
DNA endo/exo nuclease that cuts DNA facilitating repair by forming a single strand.
What is the function of DNA ligase 4 and XRCC4?
First bind DNA ligase 4 to protein complex (XRCC4), then glue DNA ends back together.
Is NHEJ required for antibody gene rearrangement?
Yes, otherwise it will never achieve the antigen specificity it needs.
Describe the NHEJ double stranded DNA repair mechanism?
1) RAG 1 and 2 causes DNA double stranded breaks within the RSS regions of 12 & 23 Bp..
2) Broken end are bound by Ku 70 &80
3) This recruits DNA PK (phosphorylates Artemis)
4) Artemis cleaves DNA hairpins forming single strands for clean processing.
5) XRCC4 binds and recruits DNA ligase 4.
6) DNA ligase seals the cuts.
What is RSS?
short sequences of DNA found right next to the V, D, and J regions.
What are the two types of RSS?
12 BP
23 BP
(each one is associated with spacers)
What is the purpose of the 12 to 23 rule?
to ensure that J elements are fused to D elements and not to V elements.
which genomic region has the two sided 12 Bp regions?
D has 12 Bp RSS regions on each side.
V and J both have 23 Bp regions.
How do RAG proteins work?
1) Bind to RSS of V, D or J region.
2) forms a paired complex (loop)
3) RAG cleaves sites next to V, D, or J region.
4) Forms a coding joint and a signal joint.
5) DS DNA activates NHEJ for repair.
what happens to the signal joint?
it is degraded
what is negative selection within B cells?
screening for self reactivity resulting in death, anergy, or even receptor editing.
what is the order of chain rearrangement?
1) heavy chain
2) light chains (kappa and Lambda)
At what stage is the B cell when it starts to undergo heavy chain gene rearrangement?
Pro- B cell
At what stage is the B cell when it starts to undergo the light chain rearrangement?
Pre-B cell
what is the order of B cell maturation?
1) Hematopoietic stem cell
2) Pro B cell (heavy chain rearrangement)
3) Pre-B cell (Light chain rearrangement, developed heavy chain is attached)
4) Immature B cell (complete antibody with heavy and light chains. Negative selection can now occur)
5) mature B cell
rearrangement has two outcomes which are?
1) productive rearrangement: heavy chain sequence created
2) Non-productive rearrangement: heavy chain not properly created.
what happens when only one allele is correctly formed in the heavy chain rearrangement?
It is considered a productive rearrangement because only one allele is needed to have a successful rearrangement.
what are the two steps to heavy chain rearrangement?
1) D and J segments are chosen and joined together
2) V is chosen and linked to the DJ segments.
what does the pre-BCR checkpoint test for?
A productive heavy chain gene rearrangement.
What does the Pre-BCR signaling do to the B cell?
1) stops heavy chain rearrangement
2) stop expressing VpreB and lambda 5
3) start light chain rearrangement
what is the function of VpreB and Lambda 5?
they both promote Pre-BCR formation by acting as surrogates for the light chain.
When do you form the Official BCR?
Only after the b cell has undergone both heavy and light chain rearrangement successfully.
When does negative selection occur?
Once you form the BCR. (after both rearrangements)
T/F Light chains contain the V, D, and J gene regions?
False. Light chain has only the V and J regions, while the heavy chain has V, D, and J regions.
How many light chain alleles are there in total?
4 (Kappa 1,2 and Lambda 1,2)
this would be 2 loci and 4 alleles.
T/F Light chain genes can e rearranged several times?
True
what is the general order of allele rearrangement for the light chain ?
Kappa 1 Kappa 2 Lambda 1 Lambda 2 (If the first one works then the cells stops rearrangement of the light chain, if non of these are productive then the cell dies)
what does negative selection look for?
Immature B cells expressing self reactive antibodies.
what are the three options when there is a self reactive B cell?
1) die
2) undergo receptor editing
3) anergy
What is receptor editing?
When a B cell is found to have a high affinity for self, the cell can either die, undergo anergy, or receptor editing which is when the cell undergoes another round of light chain rearrangement.
what does the body do with WEAK interactions between self and BCR?
1) it can undergo receptor editing
2) fall into a state of anergy.
what is anergy?
cell remains alive but cannot respond to antigen
what 2 things establish B cell central tolerance?
Negative selection and anergy.
what if self reactive cells escape into the periphery?
Clonal deletion (apoptosis) and anergy will stop them in the periphery.
