B-cell and T-cell Maturation - Diebel

Question 1

What two phenotypic markers are expressed in the stem cell stage of B-cell development?

Answer 1

• CD34
• c-kit
  
  • binds to stem-cell factor expressed on bone marrow stromal cells
  • induces the pro-B cells to proliferate and differentiate into precursor B cells (pre-B cells)

Question 2

What is a stem cell B-cell doing in the bone marrow as it is developing into an immature transitional B-cell?

Answer 2

• rearrange the genes for their heavy and light chains
• synthesize cell surface IgM
  
  • acts as initial antigen receptor (BCR)
    
    • membrane-bound immunoglobulin (mIgM)
    • signaling chains CD79a & CD79b

Question 3

When does a B-cell begin to express TdT?

Answer 3

• Progenitor B-cell stage (pro-B cell)
  
  • earliest stage of antigen-independent B-cell development
    
    • early pro-B cells express TdT alone (somatic mutation)
    • late pro-B cells have downregulated TdT

Question 4

When does a B-cell begin to express CD45R?

Answer 4

• Progenitor B-cell stage (pro-B cell)
  
  • earliest stage of antigen-independent B-cell development
    
    • early pro-B cells express TdT alone (somatic mutation)
    • intermediate pro-B cells express both TdT and CD45R
    • late pro-B cells express CD45R and have downregulated TdT

Question 5

How long do B-cells express CD45R?

Answer 5

• pro-B cell development → throughout the remainder of B-cell ontogeny
  
  • CD45R = receptor for cell growth and differentiation
  • expressed on cell surface

Question 6

Besides TdT and CD45R, what four other phenotypic markers are present during the pro-B cell stage?

Answer 6

• Early
  
  • CD43 (leukosialin)
  • RAG-1 (recombination-activating gene)
  • RAG-2 (recombination-activating gene)
• Late:
  
  • CD43 (leukosialin)
  • CD19 (BCR co-receptor)
  • CD40

Question 7

What four phenotypic markers are downregulated as the late pro-B cells pass into the pre-B cell stage?

Answer 7

• TdT
• RAG-1
• RAG-2
• CD43

Question 8

What are the two stages of a pre-B cell?

Answer 8

• large mitotically active pre-B cells
  
  • successfully rearranged their Ig heavy chain genes
• small non-dividing pre-B cells
  
  • begin to rearrange their Ig light chain genes

Question 9

What cytokine do pre-B cells produce to stimulate division and differentiation?

Answer 9

IL-7

Question 10

What two phenotypic markers are upregulated during the small pre-B cell phase as cells being to rearrange their Ig light chain genes?

Answer 10

• RAG-1
• RAG-2

Question 11

What phenotypic marker becomes expressed during the large pre-B cell stage and is present throughout the remainder of B-cell ontogeny?

Answer 11

CD20

Question 12

What is the final stage of B-cell development in the bone marrow?

Answer 12

immature B-cell

Question 13

What do immature B-cells express?

Answer 13

• Immature B-cells have successfully rearranged their light chain genes
  
  • express IgM
  • down regulate RAG-1 and RAG-2

Question 14

What do immature B-cells begin to express as they develop into a mature B-cell and exit the bone marrow?

Answer 14

both IgM and IgD on their surface

Question 15

What are the major cytokines required for B cell development?

Answer 15

• IL-7
  
  • promotes B-cell lineage development
• Blys (B-lymphocyte stimulator)
  
  • signaling through its receptor BR3
  • important for the survival of pre-immune B-cell stages from transition stage onwards
• IL-4 + IL-3 + L-BCGF (low-molecular-weight B cell growth factor)
  
  • important in initiating the process of B-cell differentiation

Question 16

What are TI-1 type antigens?

Answer 16

• predominantly bacterial cell wall components
  
  • prototypical: lipopolysaccharide (LPS)
    
    • component of the cell wall of Gram-negative bacteria

Question 17

What are TI-2 type antigens?

Answer 17

• predominantly large polysaccharide molecules with repeating antigenic determinants
  
  • e.g. Ficoll, dextran, polymeric bacterial flagellin, and poliomyelitis virus

Question 18

How does T-independent B cell activation occur with TI-1 type antigens?

Answer 18

• B cell binds to LPS through either:
  
  • TLR4 = nonspecific (polyclonal activation)
  • BCR = specific (clonal activation)
• Type 1 TI antigens can stimulate both immature and mature B cells through the use of TLR4.

Question 19

How does T-independent B cell activation occur with TI-2 type antigens?

Answer 19

• B1 B-cells bind to Type TI antigens through the cross-linking of the BCR
  
  • BCR = specific (clonal activation)
• Type 2 TI antigens can only stimulate mature B-cells through the use of the BCR

Question 20

What is the outcome of T-independent B cell activation with TI-1 type antigens?

Answer 20

ONLY IgM is produced in response to the stimulation.

Question 21

What is the outcome of T-independent B cell activation with TI-2 type antigens?

Answer 21

Mostly IgM is produced in response to this stimulation.

Question 22

What is the difference between polyclonal and clonal expansion?

Answer 22

• Clonal
  
  • group of identical cells that share a common ancestry, meaning they are derived from the same cell.
• Polyclonal
  
  • derived from many clones

Question 23

How does T-dependent B-cell activation occur?

Answer 23

• Antigen recognized by BCR in the lymph node
  
  • endocytosis
  • presentation on MHC Class II peptide
• Helper T-cell TCR recognizes antigen on B-cell MHC Class II peptide
  
  • CD40 on B-cell binds CD40L on T-cell
• Helper T-cell releases cytokines - IL-2/IL-4/IL-5
  
  • recognized by B-cell Interleukin Receptor
  • push B-cell proliferation and differentiation

Question 24

What type of B cell is activated in T-dependent B-cell activation?

Answer 24

Follicular (B-2) B cells

Question 25

What is the outcome of T-dependent activation of B-cells?

Answer 25

* B-cell class switching * Memory B-cell * Plasma Cell * IgM production * IgG production

Question 26

What are the steps of T-cell development in the bone marrow and thymus?

Answer 26

* Marrow * Hematopoietic stem cell (HSC) → Hematopoietic precursor * migrates to thymic cortex * Thymic cortex * Early thymocyte development (CD4-CD8-) * T-cell precursor → DN1 (TCRß locus rearrangement, proliferation) * DN1 → DN2 (T-cell commitment) * DN2 → DN3 (ß-selection, proliferation) * DN3 → DN4 (TCR α locus rearrangement) * Positive selection * Double positive (DP) (CD4+CD8+) → one of the following: * CD8+ (single positive) * CD4+ (single positive) * Death by neglect * Thymic medulla * Negative selection * migration to blood

Question 27

At what stage in T cell development are c-kit (CD117), CD44, and CD25 expressed?

Answer 27

* Stem cell * c-kit (CD117)⁺ * Lymphoid progenitor * c-kit (CD117)⁺ * DN1 * c-kit (CD117)⁺⁺, CD44⁺, CD25^- * migrates from bone marrow → thymus * DN2^​ * c-kit (CD117)⁺⁺⁺, CD44⁺, CD25⁺ * subcapsular cortex * T-cell lineage commitment, ß chain rearrangement * DN3 * c-kit(CD117)⁺, CD44^-, CD25⁺, CD3 * subcapsular cortex * expression of pre-TCR, ß selection * DN4 * c-kit(CD117)^low/-, CD44^-, CD25^-, CD3 * subcapsular cortex → cortex * allelic exclusion of ß-chain * α-chain locus rearrangement begins * becomes DP thymocyte

Question 28

How does a double positive (DP) T-cell decide to become CD4+ or CD8+??

Answer 28

* interacts with thymic epithelial cells * helps it decide (instructive model) * CD8 engagement signal * CD4 engagement signal

Question 29

What is the process of postive and negative selection of T-cells in the thymus?

Answer 29

* DP thymocyte interacts with cortical thymic epithelial cells * Postive selection for DP Class I and/or Class II MHC molecules * 2-5% with low-intermediate affinity interaction are selected * Positively selected CD4+ and CD8+ cells migrate to medulla * Negative selection occurs * deletion of T-cells that have high affinity to self MHC or self antigen (autoreactive receptors)

Question 30

What is the process of activation of naïve CD4+ T cells into effector T cells?

Answer 30

* Antigen recognition * NaÏve CD4+ T-cell binds APC via TCR signaling * Activation * co-stimulatory interaction between APC's CD 80/86 and T-cells' CD28 * cytokine signaling: APC releases paracrine IL-2 * Clonal Expansion * CD4+ IL-2R (CD25) binds IL-2 * cell proliferates * CD4+ releases autocrine IL-2 * Differentiation * Effector CD4+ T-cells produced * Memory CD4+ T-cells produced

Question 31

What is the process of activation of naïve CD8+ T cells into effector T cells?

Answer 31

* Antigen recognition * NaÏve CD8+ T-cell binds APC via TCR signaling * Activation * co-stimulatory interaction between APC's CD 80/86 and T-cells' CD28 * cytokine signaling: APC releases paracrine IL-2 * Clonal Expansion * CD4+ IL-2R binds IL-2 * cell proliferates * CD4+ releases autocrine IL-2 * Differentiation * Effector CD8+ T-cells produced * Memory CD8+ T-cells produced

Question 32

What are the polarizing cytokines for Th1 differentiation?

Answer 32

* IL-12 * IL-18 * IFN-gamma

Question 33

What are the polarizing cytokines for Th17 differentiation?

Answer 33

* IL-1 * IL-6 * IL-23 * TGF-beta

Question 34

What are the polarizing cytokines for Th2 differentiation?

Answer 34

* IL-4

Question 35

What are the polarizing cytokines for Treg differentiation?

Answer 35

* IL-2 * TGF-beta

Question 36

What are the polarizing cytokines for Tfh differentiation?

Answer 36

* IL-6 * IL-21