L04 Flashcards
what is expressed when the cells stay in the bone marrow
Pax5
what are the B cell-specific markers
CD45 then CD19
what is negative selection
removal of self reactive cells
what are the steps of making B cells
B cell precursor rearranges its immunoglobulin genes leading to generation of B cell receptors in the bone marrow
immature B cell bound to self cell-surface antigen is removed from repertoire (negative selection in the bone marrow
mature B cell bound to foreign Ag is activated leading to migration of B cells through the circulatory system to lymphoid organs and B-cell activation.
activated B cells give rise to plasma cells and memory cells (antibody secretion and memory cells in bone marrow and lymphoid tissue)
if B cells do not encounter Ag or see self Ag they die
what happens to pre-B cells before becoming immature B cells
H chain genes rearrange first (μ chain) moves to cell surface with Ig alpha and Ig beta and expressed with surrogate light chain (product of V preB and λ5 genes)
—> pre-B cell receptor (pBCR)
then light chains rearrange, and displace
V preB and λ5 chains (associating with H chain)
—>IgM BCR
when does D to Jh rearrangement happen
early pro-B cell
in what cells does heavy chain rearrangement stop and light chain gene rearrangement progress
Large pre-B cell
in what cells does light chain rearrangement stop
immature B cells
what does pre-BCR
Delivers signal to pre-B cell that H chain looks functional
no Ag required yet
what are the features of pre-BCR signal
Turns off RAG-1, RAG-2 genes
5 - 6 rounds of cell division
Surrogate light chain expression stops
RAG-1 and RAG-2 turned on again
L chain rearrangement starts
(RAG genes needed for gene rearrangement)
what is the most commonly expressed light chain in humans
kappa
what are the stages between stem cells and mature B cells
Stem cell
early pro-B cell
Late pro-B cells
large pre-B cell
small pre-B cell
immature B cell
mature B cell
when does Vh to DJh take place
late pro-B cell
when does V kappa to J kappa take place
from Large pre-B cell, small pre-B cell to immature B cell
when does V lambda to J lambda happen
Small pre-B cell to immature B cell
what happens when productive or nonproductive joining take place
check slide 9
what is the success rate of each rearrangement
1 in 3
what happens when pre-B cells that fail to generate non-productive re-arrangements of light chain kappa genes
they can be “rescued” by up to 10 further
rearrangements at the same locus, (as there are 5 Jk genes on each chromosome). If after all these attempts and still out of frame, then lambda locus will begin to rearrange
when are RAG 1 and 2 off
large pre-B cell
what is the function of RAG 1 and 2
lymphoid specific recombinase
what is the function of TdT
N-nucleotide
what is the function of lambda 5 and VpreB
surrogate light-chain components
what is the function of Ig alpha, Ig beta, SD45R, and Btk
signal transduction
what do immature B cells only express
IgM
what do immature B cells that bind multivalent self-antigen undergo
either
clonal deletion: cell dies by apoptosis
or
receptor editing: further light chain gene rearrangements of variable regions (get another chance)
what happens when immature B cells bind soluble self-antigen
cell becomes unresponsive
when is the heavy chain rearrangement done
Large pre-B cells
what is the surrogate light chain the product of
V preB and lambda 5 genes
how are the levels of μ and δ in anergic B cells
normal δ
low μ
Activated B cells in the periphery can develop into?
plasma cells, memory B cells
What is the fate of a pre-B cell with non productive re-arrangements of light chain genes?
They have up to 5 attempts on each kappa locus (= no. of J kappa genes) and then another four (no. of
J lambda genes) on each lambda locus
what are the 2 types of T cell genes
alpha and beta
delta and gamma
what are the types of alpha and beta T cells
CD4+ or CD8+
what is the first round of selection and what does it eliminate
positive selection
eliminates alpha and beta T cells that do not bind to self MHC
what is the second round of selection and what does it eliminate
negative selection
T cells that interact strongly with self antigen are eliminated
what do the alpha and beta T cells in the thymus develop into
thymocytes
what are the steps in developing thymocytes
1) re-arrange TCR genes (β first) and express TCR
-firstly, they rearrange TCRβ genes (similar to H chain in BCR)
-expressed along with pre-T cell receptor
-cells proliferate and then re-arrange TCR alpha genes
2) acquire other markers e.g. CD3, CD4, CD8
3) undergo positive and negative selection
what are the features of the thymus
bi-lobed organ in anterior mediastinum
each lobe divided into many lobules
each lobule has outer cortex and inner medulla
what cells are there in the thymus
lymphoid cells
epithelial cells
macrophages and dendritic cells
whare does the first round of T cell selection happen in the thymus
the cortex
whare does the second round of T cell selection happen in the thymus
the medulla
T cells express TCR with CD3 and both CD4 and CD8 and then peripheral T cells express either CD4 or CD8
true
what are the components of the CD3 complex
γ,δ,ε chains
ζ (zeta) chain dimer)
what does the CD3 complex do
transmits signal to T cell nucleus following TCR recognition of p/MHC
What is more diverse - gamma/delta TCR or alpha/beta TCR
alpha/beta
Are alpha/beta and gamma/delta expressed on the same T-cell population?
No
What percent of gamma-delta TCR is in circulation?
1-5%
Where is gamma-delta TCR found?
epithelial tissues at mucosal surfaces
Do alpha-beta and gamma-delta recognise the same antigents?
No
Do gamma/delta TCR express CD4 or CD8?
No
What is a ‘double-negative’ thymocyte?
CD3-4-8- (T cell not expressing any)
What are the products of ‘double-negative’ thymocyte?
CD3+4-8- (export+selection in periphery) and large active ‘double-positive’ thymocytes (CD3+,pTalpha:beta+,CD4+, CD8+)
What is the product of ‘double-positive’ large active thymocyte
Small resting ‘double-positive’ thymocytes
What are the products of small resting ‘double-positive’ thymocytes?
small resting ‘single-positive’ thymocytes
What are the three possibilities that T cells expressing randomly arranged alpha-beta TCRs may engage in?
- recognise self MHC & “foreign” Ag = immunity
- recognise self MHC & “self” Ag = autoimmunity
- unable to recognise self-MHC
What are the criteria for positive selection?
recognise self MHC & self peptide
What cells undergo positive selection?
double-positive T cells
Where does positive selection occur?
cortical epithelial cells in thymus
What happens if cells are not recognised?
Apoptosis
What percent of T-cells are capable of recognising own MHC?
1-2%
Where do the positively selected cells move?
Medulla
Where does the negative selection of T cells occur?
thymic dendritic cells/Mq with high affinity
What causes to T cell apoptosis?
TCR binding to MHC/self-peptide with high affinity
Why do T cells undergo apoptosis if they have high affinity?
Could induce autoimmunity
What is the ultimate goal of TCR affinity for selection?
a population of T cells with low affinity for self peptide + self MHC
What percent of T cells that survive thymic selection?
less than 5%
What are the properties of T cells that survive thymic selection?
- express TCR capable of binding self MHC
- depleted of self-reactive cells
What do CD8+T cells recognise?
Ag in association with MHC class I
What do CD4+T cells recognise?
Ag in association with MHC class II
What are the origin of thymocytes
HPC - bone marrow
Process of elimination of self-reactive T cells?
Negative
Site of T cell development and body location?
Thymus
Gene segments for alpha and beta chains that get re-arranged?
VJ, VDJ
Cells other than thymocytes present in the thymus are?
epithelial cells, APC
Alpha or beta genes rearranged first?
Beta
What is the pre-TCR?
a protein bound to rearranged TCRb that checks the assembly of b chain
What does the CD3 molecule do and why is it important?
Multi-component signalling part of TCR; leads to T cell activation following peptide/MHC antigen binding
Do gamma delta T cells normally express CD4/CD8?
No
What is positive and negative selection of T cells?
TCR must recognize self MHC alleles in thymic cortex = +ve selection, then if a T cells TCR binds
self MHC and peptide too strongly in thymic medulla will die (-ve selection)
If a T cell recognises peptide and MHC I which marker does it have on the surface?
CD8
Are the criteria for positive and negative selection of immature T cells the same?
They are similar. They both involve
ability to recognise self MHC molecules, but the affinity of TCR for peptide/MHC forms the basis of the
differences
