L09 - Lymphocyte development

Question 1

List the different lineages from HSC?

Answer 1

• Megakaryocyte
• Erythrocyte
• Granulocyte
• Lymphocyte
• Monocyte

Question 2

What is the end stage of B cell development?

Answer 2

Plasma cell to produce Ab

Question 3

Define the 2 cell physiology aspects that changes with B-cell differentiation?

Answer 3

1. Expression of cell surface molecules

2. Rearrangement status of immunoglobulin genes

Question 4

Define CD and it’s role in lymphocytes?

Answer 4

Cluster designation antigens

Expressed on leukocyte membranes, recognized by groups of monoclonal antibodies

Question 5

List some lineage markers for B cell differentiation?

Answer 5

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)

Question 6

Expression of immunoglobulin occurs in which stages of B cell differentiation?

Answer 6

pre-B cell and later stages

Pre-B cell > Immature B cell > Mature B cell

Question 7

List the immunoglobulin genes expressed in pre-B cell stages

Answer 7

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

Question 8

List the immunoglobulin genes expressed in Immature B cell?

Answer 8

monomeric (m2L2) IgM on the cell membrane

Question 9

List the immunoglobulin genes expressed in mature B cell?

Answer 9

monomeric IgM and IgD on the cell membrane

Question 10

Define successful immunoglobulin rearrangement in B cells?

Answer 10

• 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&raquo_space; λ gene gets rearranged)

> > Allelic exclusion

Question 11

Mechanism of allelic exclusion?

Answer 11

Suppresses non-expressed H and L chain loci&raquo_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

Question 12

List the sequence of B cell development stages?

Answer 12

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

Question 13

Sequence of Ig chain rearrangement in B cell development?

Answer 13

1. Pro-B cells undergo Ig heavy chain gene rearrangement
2. Pre-B cells express heavy chain + Light chain genes expression and rearrangement.
3. B cells express whole IgM (H+L) molecules on the cell surface.

Question 14

Describe the changes in H chain genes in B cell development

Answer 14

Early Pro- B cell = D-J rearranged

Late pro-B cell = V-DJ rearranged

Large pre- B cell to mature B cell = VDJ rearranged

Question 15

Describe the changes in L chain genes in B cell development

Answer 15

Germlines up to Large pre-B cell

Small pre-B cell = V-J rearrangement

Immature and Mature B cell = VJ rearranged

Question 16

Describe the changes in surface Ig in B cell development

Answer 16

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

Question 17

Role of Stromal cells in B cell development?

Answer 17

Stromal cells provide microenvironment, growth factors for developing B cells

Question 18

Describe the interaction between Stromal cells and B cells?

Answer 18

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

Question 19

B cells leave BM at what stage? Where do they mature futher?

Answer 19

Immature B cells leave bone marrow

> > further differentiation in secondary lymphoid organs (spleen, lymph nodes)

Question 20

Explain why large number of B cells form die in bone marrow?

Answer 20

Gene arrangement = error-prone process

Large number (90-95%) of developing precursor B cells fail to successfully rearrange their immunoglobulin genes

> > lost through apoptosis

Question 21

What proportion of B cells survive to be part of long-lived peripheral B cell pool?

Answer 21

5-10%

Question 22

What determines a B cell’s readiness for negative selection by antigen binding?

Answer 22

When immature B cells express functional surface IgM

Question 23

Which B cells are negatively selected against in development?

Answer 23

1) Express IgM but not IgD surface receptors;

2) Are likely to produce antibodies against the host (i.e. generate self-reactive immunoglobulins)

Question 24

Describe the negative selection process against self-reactive B cells?

Answer 24

1) B cells that bind to self-MHC molecules on self-cells&raquo_space; apoptosis/ clonal deletion
2) B cells that bind to soluble self- antigens in the peripheral blood > Anergy

Question 25

Function of receptor editing in B cell development?

Answer 25

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

Question 26

Manifestation of B cells with aberrant Ig gene rearrangement?

Answer 26

B cell tumours

Question 27

B- cell targeted therapy is employed for what diseases?

Answer 27

rheumatoid arthritis, lymphoma (e.g. rituximab = mAb against CD20)

Question 28

Locations of T cell maturation?

Answer 28

Derived from precursor cells / progenitors generated in bone marrow, migrate to and differentiate in thymus

Question 29

B and T cell development is at a constant level throughout lifetime. T or F?

Answer 29

T cell production greatest before puberty B cell production is constant

Question 30

Relate the thymus structure to stages of T cell development

Answer 30

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

Question 31

How to identify T cells through different differentiation stages?

Answer 31

1) Distinctive patterns of expression/development of cell surface markers 2) Rearrangement of Unique antigen receptors on cell surface

Question 32

Define all the surface markers expressed by T cells that travel through cortex and medulla of thymus?

Answer 32

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

Question 33

Define the T cell subsets and proportions?

Answer 33

95% of blood T cells are a:b T cells >> divided into CD4+ or CD8+ remaining 5% are γ:δ T cells.

Question 34

Rearrangement of T cell receptor genes give rise to what lineages?

Answer 34

1. α:β T cells:  Express α:β TCRs  ~95% 2. γ:δ T cells:  Express γ:δ TCRs  = remaining 5%

Question 35

Subtypes of CD4+ T- cells? How to define each subtype?

Answer 35

Classified on the basis of cytokine production:  TH1 subset secretes IL-2, IFN  TH2 subset secretes IL-4, IL-5, IL-6, IL-10

Question 36

Define the 2 selection processes in T cell maturation?

Answer 36

1. Positive selection (in thymus): ensures only T cells with TCRs having a moderate affinity for self- MHC are allowed to further develop 2. Negative selection (in thymus): eliminate T cells with TCRs that bind to self -peptides/ self-antigens TOO WELL

Question 37

List the sequence of processes that occur in T cell positive selection.

Answer 37

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

Question 38

List the sequence of processes that occur in T cell negative selection.

Answer 38

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