L09 - Lymphocyte development Flashcards
List the different lineages from HSC?
- Megakaryocyte
- Erythrocyte
- Granulocyte
- Lymphocyte
- Monocyte
What is the end stage of B cell development?
Plasma cell to produce Ab
Define the 2 cell physiology aspects that changes with B-cell differentiation?
- Expression of cell surface molecules
2. Rearrangement status of immunoglobulin genes
Define CD and it’s role in lymphocytes?
Cluster designation antigens
Expressed on leukocyte membranes, recognized by groups of monoclonal antibodies
List some lineage markers for B cell differentiation?
CD 34 > Lymphoid progenitor to Late pro-B cell
CD 19, CD 40 > Early Pro B cell to mature cell (CD19 in peripheral lymphoid organ)
Expression of immunoglobulin occurs in which stages of B cell differentiation?
pre-B cell and later stages
Pre-B cell > Immature B cell > Mature B cell
List the immunoglobulin genes expressed in pre-B cell stages
Pre-B cell:
1) µ chains in cytoplasm
2) On cell surface: µ chain (small amounts) + surrogate L chain forms part of pre-B cell receptor
List the immunoglobulin genes expressed in Immature B cell?
monomeric (m2L2) IgM on the cell membrane
List the immunoglobulin genes expressed in mature B cell?
monomeric IgM and IgD on the cell membrane
Define successful immunoglobulin rearrangement in B cells?
- 1 chromosome carrying the H chain locus;
- 1 of the chromosomes carrying the κ or λ light chain locus:
κ gene is rearranged first (only if unsuccessful»_space; λ gene gets rearranged)
> > Allelic exclusion
Mechanism of allelic exclusion?
Suppresses non-expressed H and L chain loci»_space; ensures the cell expresses Ig of:
A single H chain isotype and V region specificity, and
A single L chain isotype and V region specificity
List the sequence of B cell development stages?
Lymphocyte progenitor stem cell
>> Early pro-B cell >> Late pro-B cell >> Large pre-B cell >> Small pre-B cell >> Immature B cell >> Mature B cell
Sequence of Ig chain rearrangement in B cell development?
- Pro-B cells undergo Ig heavy chain gene rearrangement
- Pre-B cells express heavy chain + Light chain genes expression and rearrangement.
- B cells express whole IgM (H+L) molecules on the cell surface.
Describe the changes in H chain genes in B cell development
Early Pro- B cell = D-J rearranged
Late pro-B cell = V-DJ rearranged
Large pre- B cell to mature B cell = VDJ rearranged
Describe the changes in L chain genes in B cell development
Germlines up to Large pre-B cell
Small pre-B cell = V-J rearrangement
Immature and Mature B cell = VJ rearranged
Describe the changes in surface Ig in B cell development
Surface Ig absent up to Late pro-B cell
Large pre-B cell = µ heavy chain at surface as part of pre-B receptor
Small pre-B cell = +light chain in cytoplasm and nucleus
Immature B cell = IgM on cell surface
Mature B cell = IgD+ IgM from alternatively spliced H chain transcripts
Role of Stromal cells in B cell development?
Stromal cells provide microenvironment, growth factors for developing B cells
Describe the interaction between Stromal cells and B cells?
1) Early progenitor B cells bind to the stromal cells via:
a) CD44 - c-kit (on the B cell surface)
b) hyaluronic acid - stem cell factor (SCF) (on the stromal cells)
» Activate tyrosine kinase
» stimulate proliferation
2) Later make IL-7 to stimulate maturation and survival in late pro-B cells and Pre-B cells
B cells leave BM at what stage? Where do they mature futher?
Immature B cells leave bone marrow
> > further differentiation in secondary lymphoid organs (spleen, lymph nodes)
Explain why large number of B cells form die in bone marrow?
Gene arrangement = error-prone process
Large number (90-95%) of developing precursor B cells fail to successfully rearrange their immunoglobulin genes
> > lost through apoptosis
What proportion of B cells survive to be part of long-lived peripheral B cell pool?
5-10%
What determines a B cell’s readiness for negative selection by antigen binding?
When immature B cells express functional surface IgM
Which B cells are negatively selected against in development?
1) Express IgM but not IgD surface receptors;
2) Are likely to produce antibodies against the host (i.e. generate self-reactive immunoglobulins)
Describe the negative selection process against self-reactive B cells?
1) B cells that bind to self-MHC molecules on self-cells»_space; apoptosis/ clonal deletion
2) B cells that bind to soluble self- antigens in the peripheral blood > Anergy
Function of receptor editing in B cell development?
Rescue some self reactive B cells:
1) Self-reactive B cells bind to self- antigen
2) Arrest of B cells development and continue to rearrange light chain
3) If new receptor is not self-reactive anymore, B cell migrates to periphery and matures
Manifestation of B cells with aberrant Ig gene rearrangement?
B cell tumours
B- cell targeted therapy is employed for what diseases?
rheumatoid arthritis, lymphoma (e.g. rituximab = mAb against CD20)
Locations of T cell maturation?
Derived from precursor cells / progenitors generated in bone marrow,
migrate to and differentiate in thymus
B and T cell development is at a constant level throughout lifetime. T or F?
T cell production greatest before puberty
B cell production is constant
Relate the thymus structure to stages of T cell development
Developing T cells in epithelial network called Thymic Stroma, provide microenvironment for T cell development
Precursor cells enter cortex of thymic lobules from capsule
Most precursor cells (95%) destroyed as they travel through cortex and medulla (8-10 days)
Capsule > Cortex > medulla
How to identify T cells through different differentiation stages?
1) Distinctive patterns of expression/development of cell surface markers
2) Rearrangement of Unique antigen receptors on cell surface
Define all the surface markers expressed by T cells that travel through cortex and medulla of thymus?
1) @ cortex = precursor cell does not possess CD3/4/8
» double-negative thymocytes (neither CD4, CD3 or CD8-)
2) @cortico-medullary junction:
i) CD3+ (associated with TCR) = lineage marker
ii) CD4+ (= co-receptor for MHC class II, occurs on “helper” T cells)
ii) CD8+ (= co-receptor for MHC class I, occurs on “cytotoxic” T cells)
» Double-positive thymocytes (CD3+ and CD4+ or CD8+)
3) @medulla and mature T cells:
Either CD3+ and CD4+/ CD8+
Do not express CD4 and CD8
Define the T cell subsets and proportions?
95% of blood T cells are a:b T cells»_space; divided into CD4+ or CD8+
remaining 5% are γ:δ T cells.
Rearrangement of T cell receptor genes give rise to what lineages?
- α:β T cells:
Express α:β TCRs
~95% - γ:δ T cells:
Express γ:δ TCRs
= remaining 5%
Subtypes of CD4+ T- cells? How to define each subtype?
Classified on the basis of cytokine production:
TH1 subset secretes IL-2, IFN
TH2 subset secretes IL-4, IL-5, IL-6, IL-10
Define the 2 selection processes in T cell maturation?
- Positive selection (in thymus): ensures only T cells with TCRs having a moderate affinity for self- MHC are allowed to further develop
- Negative selection (in thymus): eliminate T cells with TCRs that bind to self -peptides/ self-antigens TOO WELL
List the sequence of processes that occur in T cell positive selection.
1) developing double-positive T cells with TCR are presented to self MHC (mostly thymic cortical epithelial cells)
2) screened for TCR’s ability to recognize foreign peptides
3) Rearrangement of alpha gene:
i) Recognize peptides bound to self MHC class I molecules = programmed to express CD8 co-receptors
ii) Recognize peptides bound to self MHC class II molecules = programmed to express CD4 co-receptors
4) Cells that fail positive selection die in the thymus
List the sequence of processes that occur in T cell negative selection.
1) T cells bearing TCRs that recognize self peptides:self MHC complex too well are induced to undergo apoptosis in the thymus
2) eliminate potentially self-reactive cells (mediated by dendritic cells, macrophages)
3) Only those with moderate affinity towards self-MHC are allowed to develop
