Lecture8 - HD T-Cell Maturation & Differentiation

Question 1

The epithelial component of the thymus derives bilaterally from epithelium of the ______ at _____ week of gestation

The thymic glands are colonized by hematopoietic stem cells at __ weeks of gestation.

What happens with the thymus between 4-7 weeks of gestation?

The thymus begins producing T cells when?

Answer 1

1. 3rd pharyngeal pouch, 4th
2. 7-8
3. the primordial thymic glands lose connections with the pharynx and migrate to the final position in the mediastinum forming a single bilobate gland.
4. 12-13 weeks of gestation

Question 2

Mature T cells egress the thymus and colonize peripheral lymphoid organs when?

Chronicle the development of the thymus from week 3 to week 14 of gestation:

Answer 2

1. 13-14 weeks of gestation
2. 3: epithelia of thymus derives from 3rd pharyngeal pouch

4-7: primordial thymic glands lose connection with pharynx and migrate to mediastinum and form a single bilobate gland

7-8: glands colonized by hematopoietic stem cells

12-13: thymus begins producing T cells

13-14: mature T cells egress the thymus and colonize peripheral lymphoid organs

Question 3

Why doesn’t thymectomy cause immediate immune deficiency if done after a baby is born?

DiGeorge syndrome is caused by:_____

The symptoms of DiGeorge syndrome include:

What is the most significant problem of DiGeorge syndrome that causes most other symptoms?

Answer 3

1. Because by then the peripheral T cell repertoire is established.
2. a large deletion 22q11 locus
3. heart defects, hypoparathyroidism, athymia, recurrent infection, facial features, absence of thymus and T cells
4. absence of thymus and T cell deficiency

Question 4

How can patients with DiGeorge syndrome be rescued?

Answer 4

transplantation of an allogeneic thymus graft to alleviate T cell deficiency

Allogenic = denoting, relating to, or involving tissues or cells that are genetically dissimilar and hence immunologically incompatible, although from individuals of the same species. = FROM ANOTHER PERSON

Question 5

The FOXN1 gene is on chromosome __ and encodes:

What happens in a patient with FOXN1 gene mutation?

Answer 5

17, a transcription factor need for functional maturation of thymic epithelial cell progenitors

2. CGA to TGA means no hair and no thymus.
   Thymus gland fails to form in utero because the epithelial progenitor cells don’t undergo functional differentiation and instead form cyst-like structure. They also fail to recruit hematopoietic stem cells.

Question 6

How can immune response be restored in patients with FOXN1 mutations?

What does the FOXN1 mutation tell us about how the thymus develops?

Answer 6

1. thymic implant
2. It tells us that maturation of thymic epithelial cells is required for normal architecture development, which is needed for production of T cell subsets and establishing the peripheral T cell pool.

Question 7

What part of the thymus includes the thymic epithelial cells and fibroblasts?

Where are fibroblasts found in the the thymus?

What critical functions do thymic EPITHELIAL cells provide for T cell development? (4)

Answer 7

1. Thymic stroma
2. thymic capsule and septa
3. Produce cytokines like IL1,6,7, SCF, and TSLP

express cell surface molecules like ligand Delta-like-1 for the notch receptor

Expression of MHC I or II controls selection of maturing T cells.

• expression of peripheral tissue antigens: ex –> insulin

Question 8

What are the 3 types of TEC named based on anatomical location?

Answer 8

cortical, medullary, Hassall’s

Question 9

All TEC are derived from:

Answer 9

endoderm

Question 10

What allows us to visualize the thymic cells from the cortex and from the medulla?

Answer 10

Keratin 8 for cortex

and Keratin 5 for medulla

Question 11

Macrophages and dendritic cells mature in the ______ and migrate to the ______

Answer 11

bone marrow, thymus.

Question 12

Where are macrophages and dendritic cells in the thymus?

Answer 12

scattered in cortex and medulla. high in cortico-medullary junction.

Question 13

What functions do macrophages and dendritic cells have in the thymus?

Answer 13

1. antigen presentation
2. deletion of autoreactive T cells (NEGATIVE SELECTION)
3. phagocytosis of apoptotic thymocytes

Question 14

What are the predominant lymphoid cells in the thymus?

In postnatal animals, thymocytes derive from:

Answer 14

1. thymocytes

2. HSCs

Question 15

What 4 different T cells is the thymus responsible for developing?

State the percentage for the following in thymocytes:

1. Double Positive
2. mature CD4+ T cells
3. immature CD8+ T cells?
4. immature double negative cells

Answer 15

CD4 T helper
CD8 T cytotoxic
Treg
NKT

1. 80%
2. 10%
3. 5%
4. 5%

Question 16

The production of T cells increases/decreases with age?

Answer 16

1. DECREASES

Question 17

In what age range is daily thymic output the highest?

What is the unique cell surface marker of progenitor cells in the thymus?

When is the migration of CD34pos cells initiated?

Answer 17

1. 2-10 years old
2. CD34
3. 7-8 weeks of gestation

Question 18

Why do the elderly have a less effective immune response?

Answer 18

T cell production decreases with age

Question 19

Why is cord blood a good source for HSC CD34pos cells for transplant?

What happens to the lineage potential of CD34pos cells when they enter the thymus?

Answer 19

1. Because the migration of CD34pos cells is initiated at 7-8 weeks of gestation and is highly active in the neonatal period.
2. restricted to only T lineage.

Question 20

What are the 4 key developmental events in generation of mature T cells?

Answer 20

1. T lineage committment
   - Restricted of lineage choices
2. Proliferation
   - Expansion of committed cells
3. Differentiation
   - Gaining of new surface markers
4. Maturation
   - gaining of immune functions

Question 21

What is the significance of signalling through the notch receptor?

Answer 21

terminates potential to commit to lineages other than T or NK cells

Question 22

What happens to cells following a Notch signal?

What happens to cells after they become pre-T cells?

Answer 22

cells commit to T lineage, express CD1A and begin to rearrange TCRy,d and B genes. They become pre-T cells***

2. They express CD4 and become CD4ISP.

preTa is expressed, which induces CD3 and forms the preTCR complex with TCRB.

Question 23

What happens in the B selection process?

What happens to CD3 expression during B selection? up-regulated.

Answer 23

B selection selects cells with productive and functional rearranged TCRB genes

• signaling via the preTCR.
• Cells that don’t have a good preTCR die via apoptosis.

-Cells that survive proliferate and expand, generating a lot of thymocytes with TCRaB in the thymus.

Question 24

What happens to ISP cells that survive B selection?

Answer 24

progress to express CD8 and become double positive cells.

They then rearrange TCRa genes and the d locus is deleted.

Question 25

What is the last step in T cell development following DP cell formation?

Answer 25

DP cells down modulate one of the co-receptors and mature into either single CD4 or CD8 cells.

Question 26

Summarize the entire T cell development process starting from Notch signaling.

Answer 26

1. CD34pos cell sends through Notch signal 2. CD34pos, CD7pos, CD1Aneg 3. pre-T cell. committed to T lineage. CD1Apos, CD34lo/neg rearrangement of y, d, B 4. ISP cell. CD34neg, CD1Apos, CD4pos, CD3lo. expression of preTa. B selection 5. Rearrangement of TCRa. DP cell 6. Becomes either CD4 or CD8. either way will have CD3pos and TCRaBpos

Question 27

What does positive selection of TCRaB T cells mean? The interaction of TCRaB/CD3 complex with self peptides and MHC antigens is of high or low affinity? Why is this?

Answer 27

1. Selection of T cells that recognize antigens presented by MHC molecules 2. LOW affinity - otherwise the TCR could bind the MHC molecule without the antigen low; DP cells with low affinity TCR are rescued from apoptosis and proliferate.

Question 28

What is RAG? What happens to it in positive selection? How does positive selection skew the TCRaB repertoire?

Answer 28

1 RAG stands for recombination-activating gene. 2. Expression of it is shut down so that further rearrangement cannot happen. 3. skews it toward self peptides and the potential of generating autoreactive T cell clones.

Question 29

How do bone marrow transplants tell us that developing donor T cells occur on TEC of the recipient? What happens in negative selection?

Answer 29

Patients who receive bone marrow transplant generate T cells that recognize foreign antigens in the context of their own MHC antigens and not donor MHC 2. Deletion of mature T cells that bind strongly to MHC/antigens (autoreative T cells) - negative selection results in the generation of central tolerance

Question 30

What selection generates central tolerance? DP cells with TCRaB/CD3 complex with (low OR high) affinity for self-peptide and MHC are instructed to undergo apoptosis.

Answer 30

1. negative selection | 2. HIGH AFFINITY instructed to undergo apoptosis

Question 31

Where does negative selection predominantly occur? What does the AIRE gene encode?

Answer 31

1. cortical-medullary region where there are a lot of thymic DC cells. 2. a transcription factor that induces expression of many peripheral-tissue antigens by thymic medullary epithelial cells

Question 32

How does AIRE promote central tolerance? What happens to DP cells that survive both positive and negative selection processes?

Answer 32

1. induces negative selection | 2. become either single CD4 cells or single CD8 cells.

Question 33

Selection with CD4 co-receptor and (MHC-I OR II) will generate mature CD4 cells. (select one) Selection with CD8 co-receptor and MHC-I/II will generate mature CD8 cells.

Answer 33

1. MHC-II | 2. MHC - I

Question 34

Where do mature CD4 and CD8 cells mainly reside? How do mature CD4 and Cd8 cells egress the thymus?

Answer 34

1. medulla of the thymus | 2. blood vessels in the septa in the cortical-medullary junction

Question 35

TCRyd T cells develop from: TCRyd are predominantly positive/negative on CD4 and CD8. How to TCRyd receptors differ from TCRaB receptors?

Answer 35

1. ISP cells 2. NEGATIVE 3. They bind antigens directly. - No antigen presentation to MHC required.

Question 36

What are the first yd T cells that emerge from fetal thymus? What do the TCRd1 T cells do?

Answer 36

1. cells that express d1 with y genes | 2. recognize stressed cells and lipid antigens presented by CD1B or CD1C molecules.

Question 37

Which CD proteins are noncovalently associated with B2m? Which CD proteins bing glycolipid antigens?

Answer 37

1. CD1B and CD1C2. | 2. CD1B, C, and D. B and C particularly bind bacterial glycolipid antigens.

Question 38

What specific receptor comprises the majority of circulatory yd T cells? What is the function of TCRy9d2?

Answer 38

1. TCRy9d2 | 2. recognize non-peptide pyrophosphomonoester antigens found on mycobacterium and malaria parasite

Question 39

What cells develop into NKT cells? How do NKT cells express CD4 and CD8?

Answer 39

1. DP that recognize glycolipid antigens presented by CD1D positive cortical thymocytes 2. NKT are either CD4pos or either CD4negCD8neg

Question 40

What unique markers do NKT cells express? What cytokines do NKT cells produce?

Answer 40

1. NK maker CD56 and T cell maker TCRaB/CD3 complex. 2. Th1 (IFN-y) and Th2 cytokines (IL4, IL5, IL10) 

Question 41

What observations led to the discovery of Treg?

Answer 41

Mice subjected to thymectomy between day 2 and day 4 post natal develop organspecific autoimmune diseases. The autoimmune diseases can be prevented by infusion of syngeneic T cells obtained from adult thymus or spleen, later revealed to be CD4+CD25+ T cells.

Question 42

What are Treg cells? Treg cells develop from ______ cells starting at __ weeks of gestation.

Answer 42

1. CD4posCd25pos suppressor cells with specificty for autoreactive T cells that may escape negative selection during T cell development. 2. CD3+ CD4+ T cells, 14

Question 43

What genetic mutation results in Treg deficiency? What is the acronym IPEX and how does it relate to Treg?

Answer 43

1. FOXP3 gene mutatiln (Xp11.23-Xq13.3) 2. Used to describe autoimmune disease resulting from FOXp3 mutation. Immune Dysregulation Poly- Endocrinopathy X-linked inheritance

Question 44

What is the difference in USEAGE of the FOXP3 gene and FOXN1 gene?

Answer 44

FOX P3 gene = for development of the Tregs FOXN1 = for development of Thymic Epithelial Cells (TEC)

Question 45

High Treg prevents what?

Answer 45

HIGH TREG prevents the killing of tumor cells | - Increases in the levels of Treg have been found associated with certain types of cancer

Question 46

Where are two areas that Tregs develop?

Answer 46

1. In the thymus - CD3+ and CD4+ 2. IN the periphery - CD4+ by TGF-B

Question 47

What is responsible for peanut allergies?

Answer 47

T helper 3 (Th3): oral tolerance induction - if no oral tolerance