Humoral Immunity: Antibodies and the Life Cycle of B Cells Flashcards
What are the 2 main phases in a B cell’s life cycle and which is antigen-dependant?
- Before activation - Antigen independant
- After activation - Antigen-dependent
Describe the structure (all the chains) of immunoglobulin
How many different types (classes) of Ig heavy chain are there?
One for each class of Ig (IgM, IgD …)
Name the 2 chains (domains) in Ig light chain
kappa and lambda
Name the domains in an antibody in terms of variable and constant regions
What holds together the heavy and light chains in Ig and the heavy chains to each other?
Disulphide bonds between cystein and other charged amino acids
On Ig, there is also {?} groups on the CH2 region to promote interaction between antibodies and {?}.
On Ig, there is also carbohydrate glycosylation groups on the CH2 region to promote interaction between antibodies and other immune cells it recruits
What is the Fab fragment?
The variable fragment (VL + VH) + CH1 + CL (the first constant regions)
What is the Fc fragment made of?
CH2 + CH3
What are CDRs?
Complimentary determining regions on the variable domains - are where the antibody interacts with antigens
What is the difference between a fragment and a domain?
Domain is like just VL or CH3 on a single chain. Whereas, fragment is multiple domains possibly accross multiple chains such as the Fab grament which is VL + VH
How many CDRs do we have in total on Ig?
- 3 Light chain (L1, L2, L3) + 3 Heavy chain (H1, H2, H3)
- So 6 x 2 = 12
Name the 4 general functions that an antibody can do to combat pathogens
- Virus and toxin neutralisation
- Opsonisation + ADCP
- Complement fixing/ MAC formation (CDC)
- Opsonisation + ADCC
ADCC = antibody dependant cellular cytotoxicity ADCP = antibody dependant cellular phagocytosis
What is meant by complement fixing/MAC formation?
Antibodies (especially IgM) can form large immune complexes with the pathogen which can agglutinate pathogens and recruit complement molecules - promotes inflammation, phagocytosis and formation of membrane attack complexes (MAC)
Name the 5 antibody classes
- IgG
- IgD
- IgE
- IgA
- IgM
What differs between the classes of antibodies?
Heavy chain constant regions
- variable regions are obviously different but are the same for antibodies produced in the same B cell
How is IgA able to be secreted into the mucus?
It has a secretory component wrapped around it
Describe the different roles of the 5 different classes of antibodies
Ig{?} is the main antibody in the serum, followed by Ig{?}
IgG is the main antibody in the serum, followed by IgA
Only Ig{?} and Ig{?} can fix complement
Only IgM and IgG can fix complement
Only Ig{?} crosses the placenta to give immunity to a foetus
Only IgG crosses the placenta to give immunity to a foetus
Ig{?} is the first antibody produced and is also the best at fixing complement
IgM is the first antibody produced and is also the best at fixing complement
Ig{?} is the BCR that indicates that the B cell is mature, is the only antibody that is not secreted as it does not play a role in the defense against pathogens or parasites
IgD is the BCR that indicates that the B cell is mature, is the only antibody that is not secreted as it does not play a role in the defense against pathogens or parasites
Ig{?} is the main antibody in secondary responses as it is only formed after affinity maturation (when the B cell can undergo class switching). Ig{?} is another late comer and this is secreted into mucus, tears and saliva.
IgG is the main antibody in secondary responses as it is only formed after affinity maturation (when the B cell can undergo class switching).
IgA is another late comer and this is secreted into mucus, tears and saliva.
Ig{?} is involved in allergic reactions and is very good at recruiting mast cells and basophils for attack on parasites that can not be phagocytosed.
IgE is involved in allergic reactions and is very good at recruiting mast cells and basophils for attack on parasites that can not be phagocytosed.
Which is the only part of an immunoglobulin that class switching affects?
Heavy chain constant region - all the others (including variable regions) are the same
Name the 2 types of class switching
Minor (differential splicing)
Major (DNA recombination)
Minor class switching is called this way as it {?}.
Minor class switching is called this way as it does not affect the DNA of the B cell itself (mRNA levels)
Minor class switching is from Ig{?} to Ig{?}
Minor class switching is from IgM to IgD
Major class switching involves B cell DNA {?}.
Major class switching involves B cell DNA recombination.
B cells intitiate class switching due to {?} released by {?}
B cells intitiate class switching due to cytokines released by T helper cells (TH1, TH2 and Treg)
Name the 3 things that class switch recombination needs
- Cytokine signals from TH2 cells
- Switch regions between Ig gene segements
- AID and DSB repair proteins
IgM can switch to Ig{?}, {?} and {?} as major class switching can only occur {?} and IgM constant region (C mu) is the most {?}
IgM can switch to IgG, A and E as major class switching can only occur downstream and IgM constant region (C mu) is the most upstream
Name the 2 main proteins that are involved in class switch recombination (the mechanism for major class switching of a B cell)
AID and DSB
Is this right?? Or are they used for somatic hyper mutation
Describe the differences in the structure of a secreted Ig and a membrane Ig (BCR)
Describe the mechanism for how Ig is made into either secreted form or BCR form (membrane bound)
(Need to watch a video on this) C mu is made of 4 regions (mu1 - mu4) and there is a tail piece at the end of mu 4 followed by a stop codon
- M1 and M2 is after that and codes for the transmembrane region and the cytoplasmic tail with another polyA tail and stop codon. This region is spliced out or is kept by differential splicing, is kept if the antibody is secreted
Name the 2 stages of B cell development
- Antigen independant
- Antigen dependant (outlined)
In the bone marrow, a pro-B cell will undergo {?} and {?} recombination of the heavy chain variable region to become a pre-B cell. This pre-B cell will also produce a placeholder light chain.
In the bone marrow, a pro-B cell will undergo D→J and V→DJ recombination of the heavy chain variable region to become a pre-B cell.
This pre-B cell will also produce a placeholder light chain.
A circulating mature B cell will further increase its ability to bind to the pathogen once it encounters it by a process called {?} in the {?}. Only the best will survive.
A circulating mature B cell will further increase its ability to bind to the pathogen once it encounters it by a process called affinity maturation in the germinal centre. Only the best will survive.
Straight after affinity maturation, B cells undergo {?} (upon receiving information about the pathogen) to produce the appropriate antibodies. So antibodies will go from IgM to either Ig{?} or Ig{?
Straight after affinity maturation, B cells undergo class switching (upon receiving information about the pathogen) to produce the appropriate antibodies. So antibodies will go from IgM to either IgG or IgA
- But some if the IgM cells will not class switch and will differentiate straight into plasma cells producing IgM as a first defence
In VDJ recombination in a B cell, which chain (light or heavy) does NOT contain the D segments?
Light chain does not contain them
Overview of V(D)J recombination in B cells to form variation in antibodies
J or D/J codes for CDR3 which the the most variable region in an antibody
Which region in a B cell (V, D, J or C) codes for CDR3 (the most variable region in an antibody)?
J or D/J
In VJ (not VDJ) recmobination in a B cell, VJ recombination occurs and there is an extra J segment added. What happens to this? Also, before every V segment is a leader section that tells the cell which segment is which. This is for the formation of κ chain, λ chain is more complex.
It is spliced out.
VDJ recombination
RSS (recombination signal sequences) are made of turns consisting of a {?} and {?} separated by a spacer
RSS (recombination signal sequences) are made of turns consisting of a heptamer and nonamer separated by a spacer
RSS (recombination signal sequences) have 2 types of turns: {?} and {?}.
RSS (recombination signal sequences) have 2 types of turns: two turn (23bp spacer) and one turn (12 bp spacer).
- The reason why we have 2 types of turns is thsast recombiantion only occurs between a segment with a 12 bp spacer with a segment with a 23 bp spacer.
- So no 12 with 12 or 23 with 23.
In the image below, what do the red triangles represent as opposed to the blue triangles?
Red triangles = One turn RSS
Blue triangles = Two turn RSS
Describe what is happening in the image below. What is the difference between the minor hairpin and the major?
This is a simple diagram for VJ recombination.
RAG 1 and 2 bind to the turns, pulling them together to form a hairpin.
- minor hairpin is between the two strands of DNA
- major hairpin is the whole DNA folded in half
Describe what P nucleotide addition is
Affinity maturation in the spleen/lymph node for a B cell involves {?} and {?} in the dark zone and then they migrate to the light zone for {?}. This process is repeated multiple times.
Affinity maturation in the spleen/lymph node for a B cell involves clonal expansion and somatic hypermutation in the dark zone and then they migrate to the light zone for selection. This process is repeated multiple times.
After affinity maturation, a B cell will undergo {?} so that it has the appropriate effector functions for the pathogen in question.
After affinity maturation, a B cell will undergo class switching so that it has the appropriate effector functions for the pathogen in question.
After activation (including class swithcing and affinity maturation) B cells will become {?} cells and a few will become {?} cells.
After activation (including class switching and affinity maturation) B cells will become B plasma cells and a few will become Memory B cells.
Explain what is meant by how B cell (full) activation in the lymph nodes requires triple verification.
This is similar to what we talked abput in the T cell lecture
In order not to accidentally activate the B cells, first the B cell needs to:
- encounter, internalise pathogen and present antigen on surface MHC2 to Thelper
- needs to be activated by a T cell that is in turn activated by a dendritic cell
- the dendritic cell will have also been presenting the pathogen antigen
- third signal is the cytokines
Affinity maturation is a process to improve the affinity of an antibody to an antigen. This is done by generating mutations in the {?}.
Affinity maturation is a process to improve the affinity of an antibody to an antigen. This is done by generating mutations in the variable region genes of a BCR
