Lymphocyte Ontogeny And Lymphopoiesis

Question 1

What processes enable diversity in TCR and BCR?
What third process further diversifies Ig in B Cells? What cells aid this process?

Answer 1

Combinatorial diversity and junctional diversity in TCR and BCR
Somatic hypermutation in B cell IgG

Question 2

What gene segments and enzyme complexes are crucial for VDJ rearrangement?

Answer 2

Recombination signal sequences (RSS)
Recombination-activating gene (RAG) enzyme complexes
RAG1 and RAG2 recognize and bind to RSS’s adjacent to different V,D, and J segments

Question 3

Which receptors only use V and J rearrangement?

Answer 3

TCR alpha chain
BCR (Ig) light chain
(BCR heavy chain uses V, D, and J rearrangements)

Question 4

What is the role of DNA protein kinase in combinatorial diversity?

Answer 4

DNA-PK reanneals the cut ends (by RAG enzymes) in complex with Artemis nuclear and DNA ligaments IV
(Foals lacking DNA-PK have SCID)

Question 5

Which T cell subset display decreased antigenic diversity?

Answer 5

Gamma-delta (yd) T-cells, due to reduced diversity in V-segments

Question 6

What is the role of terminal deoxynucleotidyl transferase (TdT) in junctional diversity?

Answer 6

TdT is a DNA polymerase that adds variable number of nucleotides to the V,D, and J exons during rearrangement. These additional nucleotides are called N regions

Question 7

What happens if a TCR or Ig chain fails to form?

Answer 7

If on the first chromosome, then rearrangement moves to the second chromosome. If both fail, then apoptosis occurs

Question 8

How does TdT expression change as B-cell’s mature?

Answer 8

TdT expression decreases during maturation, and does not increase light-chain diversity

Question 9

Where does somatic hypermutation occur?

Answer 9

Somatic hypermutation occurs in proliferating B cells that have been activated by antigen-bearing Th cells. It is restricted to the BCR genes in the complementarity determining regions (CDR) that bind the antigen.

Question 10

How does activation-induced deaminase (AID) mediate somatic hypermutation?

Answer 10

AID delaminates cytosine to uracil, resulting in a U:G mismatch.
These mismatches are removed by base-excision repair enzymes.
These removals are repaired by DNA polymerases that create mutations in one or a few nucleotides surrounding the mismatch.

Question 11

Where does B-cell lymphopoeisis occur in different animal groups?

Answer 11

Mammals - fetal liver, transitions to bone marrow
Birds - bursa of fabricius
Fish - kidneys
Amphibians - spleen, bone marrow, kidney

Question 12

What is the initial antibody isotype (the initial BCR) expressed by all developing mammalian B-cells?

Answer 12

IgM

Question 13

What interleukin is important in initial proliferation of B-cell progenitors?

Answer 13

IL-7

Question 14

Explain the sequence of VDJ rearrangement in developing B-cells

Answer 14

Heavy chain D-J segments recombine first, followed by V segments to the rearranged DJ segment
The recombined heavy chain is tested to see if it can bind to a surrogate light chain. (First checkpoint)
If not, the second chromosome is recombined
If so, then the BCR is checked for self-reactivity (second checkpoint)

Question 15

What is the third checkpoint in BCR production?

Answer 15

After the light chain is recombined and if it can bind the heavy chain, the newly formed BCR is exposed to self-antigen (and those with affinity are deleted)

Question 16

When do B-cell precursors start to express CD21?

Answer 16

As cytoplasmic IgM is exported to the surface membrane

Question 17

B-cells initially express which Ig isotypes?

Answer 17

IgM (because C mu is the first constant region) and some IgD
Will exhibit class switching later after antigen and T-helper activation in the periphery

Question 18

B-1 B cells express which cell surface marker? Where do they mostly reside?

Answer 18

CD5
Reside in pleural and peritoneal cavities

Question 19

Which species do B-1 cells make up the majority of B-cells?

Answer 19

Ruminants and rabbits

Question 20

Why is there less BCR diversity in B-1 B cells? What is their antigen specificity honed to?

Answer 20

They lack TdT expression and do not undergo somatic hypermutation, and they have fewer possible DJ and VDJ permutations
Their specificity is honed to bacterial polysaccharides and lipids

Question 21

What is an inflammatory response advantage that B-1 B cells have over B-2 B cells?

Answer 21

They are capable of activation independent of Th-cells

Question 22

Where do marginal zone B-cells reside? How are they similar to B-1 B cells?

Answer 22

They residency in the marginal zone of the spleen
They can respond to antigen in a T-helper independent manner

Question 24

Initial T-cell precursors are produced from CLP then migrate to the ____ for maturation

Answer 24

Thymus

Question 25

What signaling pathway driven by thymic stromal cells drives T-cell development and is essential for T-cell vs. B-cell fate decision?

Answer 25

Notch signaling

Question 26

In most species, 90% of T-cells have what type of TCR?

Answer 26

Alpha-beta (vs. gamma-delta)

Question 27

ab TCR are only capable of recognizing antigen when complexed with ______

Answer 27

MCH I or MHCII molecules

Question 28

What are two characteristics of yd TCRs?

Answer 28

Capable of recognizing antigen not associated with MHC Narrow range, capable of binding to lipid antigens, phosphorylated ligands, and heat shock proteins

Question 29

What are the earliest T cell progenitors in the thymus?

Answer 29

Double negative (lack expression of CD4 or CD8)

Question 30

After a functional beta TCR is produced, TCRa rearrangement occurs in what cells?

Answer 30

CD4+/CD8+ (double positive cells)

Question 31

Double positive CD3 T-cells are selected through their interaction with ____

Answer 31

MHC Cells that interact with MHCII cells will become CD4 T cells (Th1, Th2, Th17, poss Treg) Cells that interact with MCH I will become CD8 T cells (Cytotoxic T-cells)

Question 32

Which cells produce peripheral antigens to enable negative selection of T-cells? What gene is required?

Answer 32

Thymic medullary epithelial and dendritic cells AIRE (an auto immune regulatory gene)

Question 33

Natural killer cells are a subpopulation of what T-cells?

Answer 33

alpha-beta T-cells

Question 34

NK cells may express what cell markers?

Answer 34

NK1.1 Variable CD4/CD8 expression CD16, CD56 Produce granzyme

Question 35

NK cells recognize antigen presented in what molecules?

Answer 35

CD1d (Enhanced ability to recognize lipid and glycolipid antigen)

Question 36

What receptors do NK cells lack? What do they express?

Answer 36

Lack TCR, BCR, and CD3 Express NK-receptors, which are not recombined but are constitutively expressed

Question 37

What are two mechanisms that NK cells may recognize altered host cells?

Answer 37

Normal cell surface proteins with structural modifications (secondary to intracellular stress or viral infection) Altered MHC 1 expression (normal MHC-1 expression may inhibit cell killing)