B cells and antibodies Flashcards
Does a PAx5 KO mouse still have pro-B cells?
Yes
Pax5 needed to get from pro to pre
Is monospecificity guaranteed with allelic exclusion?
Yes
Which cells are B cell IgM(low)IgD(+)
and which IgM(high)IgD(low)?
mature
immature
Name at least 4 characteristics of plasma cells.
- produce high amounts of high affinity antibodies
- relocate to BM after leaving GC (specialized niche for long term survival; except if produced in mucosa)
- there are 2 types: short lived (red pulp) and long lived (BM)
- have abundant rER, well developed Golgi
Name at least 4 characteristics of memory B cells.
- generated during GC reaction
- long lived
- express surface BCR, but do not secrete antibodies
- are in a resting state and recirculate in the body
- are activated directly after Ag encounter (can differentiate rapidly into Ab producing cells)
Describe 6 phases of B cell development. Which are they, what is happening in relation to gene rearrangement, which molecules are expressed on the cell surface?
- early pro-B cell
- DJ rearrangement of the heavy chain
- germline light chain
- nothing on the surface - late pro-B cell
- VDJ rearrangement of the heavy chain
- germline light chain
- nothing on the surface - large pre-B cell
- VDJ rearranged = heavy chain finished
- germline light chain
- pre-B receptor (= mi heavy chain + VpreB + lambda5 instead of light chain) –> signal for successful rearrangement of heavy chain upon clustering of the receptors via ligh chain substitutes dimerization - small pre-B cell
- heavy chain finished
- VJ recombination of kappa chain first (if unsuccessful, lambda rearrangement)
- nothing on the surface (mi heavy chain is internalized) - immature B cell
- heavy chain rearranged
- light chain rearranged
- IgM expressed on the cell surface - mature B cell
- alternative H-chain splicing leading to IgD expression on the surface too (besides IgM)
Ž - Where are B cells generated in birds and what is equivalent of that in mammals?
bursa of Fabricious
bone marrow and fetal liver
Ž - What were Max Cooper’s observations regarding levels of antibodies compared to severity of Herpes lesions in Wiscott-Aldrich syndrome vs X-linked agammaglobulinemia?
noticed, that despite higher levels of ABs in WAS, Herpes lesions were more severe and vice versa
meaning that AB alone cannot be responsible for viral protection
Ž - Which steps of B cell development happen in bone marrow and which in periphery?
BM: generation of BCR and negative selection of cells (self-reactive are removed), AB secretion, memory cells reside in BM too
periphery: migration to lymph nodes and activation by recognizing Ag (positive selection), partly AB secretion
Ž - BCR - Describe the structure of BCR - crystal structure AND the complex of coreceptors associated with it.
2 x heavy chain, 2 x light
variable domain at the N-end of each, the other 3 are constant
connections by disulphide bonds in the hinge region
membrane bound while BCR
Igalpha and Igbeta for transfer of signal into the cell (ITAMs)
co-receptors next to it: CD19, CD21, CD81
Ž - BCR - Which chain contains D segments in the genome in which does not? How many genes for heavy and how many for light chain do we have?
heavy = VDJ light = VJ only
heavy = 1 light = 2 (kappa and lambda)
Ž - BCR - How do BCR genes that will undergo rearrangement get close enough to each other so that Rag can connect 2 RSSs?
whole locus contraction happens
Ž - Antibodies can recognize virually any structure. How is this diversity achieved?
- a lot of different V/D/J segments for both heavy and light chain
- 2 alternative light chains
= 2,6 x 10^6 combinations from that alone - additionally, random nucleotides are inserted during VDJ recombination
- somatic hypermutation afterwards to increase affintiy
Ž - Which transcription factor leads to B cell development from common lymphoid precursor and what are the alternatives?
Which genes are expressed that lead to B cell fate?
B cell development = E2A (and EBF)
Notch = T cells
Id2 = NK cells
E2A and EBF target genes:
- Pax5
- Igalpha and Igbeta
- Rag
- VpreB, lambda5
Ž - Some BCRs recognize self-molecules. What happens with them in bone marrow and what in the spleen?
a) if they do not recognize Ag in the BM:
mature normally, go in the periphery and have IgM and IgD on the surface
b) if they recognize multivalent self-molecules:
in BM, they undergo receptor editing or cell death
in spleen, receptor editing is not an option anymore, so they die
c) if they bind soluble self-antigens that x-link the BCR:
become anergic, end up having IgD»IgM, migrate to periphery, fail to recieve survival signs because they do not recognize Ags, die
d) if they bind self-Ag, but it is either unaccessible to them or they bind it with very low affinity:
mature normally, but are clonally ignorant because even if the Ag is present, it is unable to activate them because its concentration is too low
Ž - What are transitional B cells?
transitional B cells are IgM+ immature B cells that migrated to the spleen (cca 10-20% of all immature B cells generated) and survived negative selection there, but have not undergone positive selection yet
Ž - Which types of transitional B cells exist and what are their main characteristics?
T1: IgM > IgD, CD21 and CD23 negative, present in T cell zone in the spleen (PALS); recent immigrants from the bone marrow
T2: IgM & IgD
T3: IgM < IgD
Ž - Besides transitional B cells, 2 other major types exist. Where do we find them?
marginal zone B cells in spleen only
follicular B cells in spleen and lymph nodes
Ž - What are marginal B cells?
long lived B cells in the spleen, do not recirculate
are the first ones to come in contact with blood-borne pathogens -> differentiate in IgM-secreting plasma cells (fast) = increased reactivity, but have restricted antigen specificity
can be activated by thymus-dependent AND independent antigens
Ž - What are follicular B cells?
B cells located in the primary follicle (spleen and lymph nodes) need to be activated by T cells upon Ag recognition -> form GCs and differentiate into Ab secreting plasma cells and memory cells undergo affinity maturation and class switching
Ž - In which 3 classes (subsets) do we sort B cells? Name a couple of characteristics of each.
B-1: in fetus, very limited recombination and somatic hypermutation, found in body cavities
B-2: a) conventional (follicular) ones - extensive gene rearrangement, undergo class switching (mostly IgG), need T cell help for activation, can become memory cells
b) marginal zone B cells: found in spleen only, long-lived, mainly IgM on the surface, can be activated by TI and TD antigens
Ž - How is B cell tolerance against self-tissue maintained?
B cell encounter Ag during development in the secondary lymphoid organs
if they recongize self-antigens, they do not undergo deletion as T cells, but rather receptor editing and anergy
= consequence of the BCR signaling strength
= more signaling leads to downregulation of BCRs
= autoreactive B cells persist in the mature repertoir, but are anergic
Ž - BCR - Which interactions (bonds) are formed between receptor and Ag?
noncovalent (electrostatic, hydrogen, VdW, hydrophobic)
Ž - BCR - In which regions (V/D/J) are hypervariable sequences located? Where are they found in the final structure of the receptor?
in V region
3 in light, 3 in heavy chain
form antigen binding site
