Immunology Exam 2 study guide

What are the names of the four known TCR chains?

1. alpha

2. beta

3. gamma

4. delta

How do the four TCR chains pair up to make TCR?

• alpha and beta

• delta and gamma

Which of the four TCR chains are heavy chains?

beta and delta

Which of the four TCR chains are light chains

alpha and gamma

What must the binding region of the TCR recognize before activation?

Must recognize Ag and MHC. CD4 for MHC II, CD8 for MHC I

How are the genes that encode the TCR ordered on the heavy chain?

VDJC

How are the genes that encode the TCR ordered on the light chain?

VJC

How is the T cell chain disorderly? What does this allow?

the alpha chain can be split up between delta, while beta and gamma have their own separate sections of the genome. This allows for delta to be cut out of alpha

In what order do TCR genes rearrange and why do we call it a race?

Rearrangement race between Beta, delta, and gamma first. Delta and gamma have to rearrange first in order to turn off the beta chain, but if Beta wins delta and gamma are turned off

What gene combination is more likely to win the TCR rearrangement race? Why?

Alpha and Beta are more likely to win that race. Beta has a surrogate light chain, while delta and gamma have to be coded to work

Are TCRs ever secreted? Do they go through affinity maturation?

Nope! they have no affinity maturation

What does a beta heavy chain use to test its rearrangement?

a surrogate light chain

Is there allelic exclusion in the TCR?

There is allelic exclusion with the recombination race, but not on alpha chain. it is rare but possible to have 2 different types of alpha chains.

If beta wins the race, there is allelic exclusion of delta and gamma genes. there is also allelic exclusion with beta chains against other types of beta

What type of selection does a T cell go through? How does this differe from B cell testing?

T cell does negative selection, as well as positive selection. B cell only does negative selection in the bone marrow

Is B cell recombination orderly or disorderly?

orderly, with normal sequence of allele

Do B cells do allelic exclusion?

yes

What occurs in B cells after activation?

1. affinity maturation

2. class switch

3. divide to make effectors and memory cells

Before activation how is B cell affinity?

low

After activation, how is affinity binding?

high

Where do B cells do negative selection?

the bone marrow

What is characteristic of T cell recombination?

Race for recombination

Do T cells have allelic exclusion?

yes, but not on alpha chain

After T cell activation, there is no…

1. affinity maturation

2. isotypes/class switching

3. dividing to make effector and memory cells

Before activation, how is TCR binding affinity?

low

After activation, how is TCR binding affinity?

low

Where do T cells do negative and positive selection?

• negative in BM

• positive in thymus

Why would it be a problem to do sequential recombination in T cells first?

the delta chain would get deleted

What is weird about delta chain recombination?

just delta has multiple D boxes

What does CD2 bind?

LFA3

What does CD5 bind?

CD72

What does LFA1 bind?

ICAM-1

What does CD45R bind?

CD45, CD22

What do adhesion proteins, such as CD2, CD5, LFA1, and CD45R help with?

help Th bond and stay attached to the APC

What adhesion proteins appear on Th cells?

CD2, CD45, LFA1, and CD45R

What adhesion proteins appear on Th cells?

CD2, CD5, LFA1, CD45R

What are ITAMs?

Immunoreceptor Tyrosine Based activation motiv.

which chains make up the TCR-CD3 complex?

gamma, epsilon, delta, zeta, and eta.

How are ITAMs paired in TCR-CD3 complex?

• gamma and epsilon

• delta and epsilon

• zeta and zeta

• zeta and eta

What is the complex of TCR ITAMs called? What is it made up of?

• CD3 is what

• one gamma and epsilon

• one delta and epsilon

• and one of either zeta and zeta or zeta and eta

How many ITAMS are on each chain of of the TCR-CD3 complex?

• 1 on gamma

• 1 on epsilon

• 1 on delta

• 3 on zeta and eta

What is the first type of differentiation for a hemapoietic stem cell?

Myeloid and lymphoid progenitors

What cells do lymphoid progenitors make?

lymphocytes (NKC, B cells, T cells)

What do Myeloid progenitors become?

• monocytes/macrophages

• dendritic cells

• osteoclast

• megakaryocyte

• platelets

• mast cells

• basophil, eosinophil, neutrophil

• erythrocytes

What type of cells support hematopoiesis?

Stromal macrophage cells, which supply cytokines

What protein influences what cells will become T cells or B cells?

Notch 1

How can we determine if a cell is a hemapoietic stem cell?

If it has CKit and Sca1

What are the six stages of T cells development in the thymus?

• DN1

• DN2

• DN3

• DN4

• Double positive

• single positive

What characterizes DN1?

• notch 1

• CD44

• CKit

• Sca1

What characterizes DN2

• CKit

• Sca1

• CD44

• IL-2R (CD25)

What characterizes DN3?

• CKit

• Sca1

• IL-2R (CD25)

What characterizes DN4

• fully arranged TCR, apoptosis is turned back on

What characterizes Double Positive T cell?

has both Cd4 and CD8

What characterizes single positive T cell?

Has either CD4 or CD8, or neither

What is the importance of Notch1 and CD44? When is CD44 present?

• Notch +1 is needed for T cells

• CD44 is present during Lymphoid progenitor, DN1, and DN2

When does the rearrangement race begin?

beginning of DN2

At what stage is the TCR successfully expressed on the surface?

at the end of DN4

At what stage do we need IL-2?

We need IL-2 during stages DN2 and DN3.

what is the IL-2 receptor called?

IL-2R, or CD25

Why is IL-2 important?

it prevents apoptosis, and is a signal to divide.

Why does the T cell turn on apoptosis?

To prevent autoimmune diseases in case of T cell arrangement failure. You want to kill it if it doesn’t rearrange right.

In which situations would a T cell undergo apoptosis?

1. Both beta chains fail

2. Both gamma and delta fail

3. Both alpha chains fail

4. Positive selection

5. Negative selection

What turns off apoptosis?

• Positive selection

• Successful TCR recombination

• Recombination in IL-2

When is apoptosis turned off in TCR rearrangement?

end of DN4

Explain the process of positive selection

 APC presents Self-Ag to a DP to see if it can bind to MHC II or MHC I.

Why does negative selection sometimes happen simultaneously with positive selection?

When you’re doing positive selection, if TCR binds too tightly, negative selection can be done, in the Cortex.

If negative selection does not happen when positive selection happens, why does negative selection happen right afterwards? Where does this occur?

This occurs in the medulla. You still want to eliminate the cells that are too self-reactive.

During what stages of thymocyte development does positive and negative selection occur?

Positive selection happens to DP, and negative selection happens to SP.

Where in the thymus does positive and negative selection occur?

• Positive selection occurs in the cortex

• Negative selection occurs in the medulla. 

affinity

strength of binding

avidity

# of proteins binding, # of binding sites

Besides 'binding' in general, what is positive selection specifically testing the TCR for?

Testing to see if TCR binds to MHC I and MHC II.

Besides 'binding' in general, what is negative selection specifically testing the TCR for?

Testing the TCR’s binding strength, whether it is too strong or not.

 Given the tasks at hand, what about positive and negative selection is complicated about this process with respects to the antigen that the APC has to offer in the thymus?

The antigen is self-antigen.

What type of death occurs with positive selection?

Death by neglect

What type of death occurs with negative selection?

apoptosis

Instructive model

the extracellular signal directly instructs the cell which lineage path to take. A DP thymocyte expresses both CD4 and CD8. If its TCR happens to bind an MHC II molecule, the co-receptor CD4 engages and generates a specific, strong CD4-type signal, with signal activity instructing the cell to turn on CD4-specific transcription factors and silence the CD8 gene. If it happens to bind an MHC I molecule, the co-receptor CD8 engages and generates a specific, strong CD8-type signal, with signal activity instructing the cell to turn on CD8- specific transcription factors and silence the CD4 gene.

Stochastic model

lineage commitment is a completely random genetic event. A DP thymocyte randomly downregulates on of its co-receptors due to internal gene fluctuations. A cell might randomly shut off CD8, leaving it as a temporary CD4+ cell. If that cell’s TCR happens to recognize MHC Class II, it receives a survival signal and matures into CD4+ T cell. If that cell’s TCR actually recognized MHC class I, it cannot signal properly without CD8. Lacking a survival signal, it fails checkpoint and dies by apoptosis.

kinetic model

every DP thymocyte initially downregulates CD8 transcription when it initiates positive selection, temporarily turning into a cell trying to see if it can be CD4+. If the TCR engaged with MHC class II, the remaining surface CD4 co-receptors keep signaling continuously. This sustained, uninterrupted signal kinetic programs the cell to permanently commit to the CD4 lineage. If the TCR engaged with MHC class I, the signal suddenly drops or stops because the cell just downregulated its matching CD8 co-receptors. This interruption/cessation of signaling serves as a specific checkpoint cue. The cell interprets the silence as a command to initiate a coreceptor rescue, turning CD8 back on, silencing CD4, and committing to the CD8 lineage.

What are the categories of CD4+ cells?

1. Th1→ virus, intracellular infections

2. Th2→ bacteria

3. Th17→ fungi

4. Treg/suppresors→ downregulate immune response

What are the distinctions of categories of CD4+ cells based on?

cytokines being made

Categories of CD8+

only make Tc, which make toxic granules to kill infected cells

What is the first signal in naive T cell activation?

TCR sees Ag on MHC

What is the second signal in T cell activation?

• CD28 binds B7-CD80/86

What is the third signal and what happens after it?

IL-2R binds IL-2, and then it divides!

How long can effector T cells last?

3-10 days.

Why do we not do point mutations on our TCR?

You wouldn’t want to do affinity maturation and increase affinity to self-Ag.

 How does the second signal in T cell activation decrease autoimmunity?

Won’t express unless there is antigen in the cell.

What is at the bottom of CD8? What does it do?

p56LCK, phosphorylates ITAMs

What is Zap70 and what does it do?

Binds to phosphorylated ITAMS and starts a signal cascade.

 What is the end result of a signal cascade?

• Leads to a gene change that would result in the production of more cytokines or a different type of cytokines, leads to more granulocytes

• Ultimate goal is gene regulation 

What is a lipid raft?

Cholesterol, sphingolipid, and phospholipids.

What role do lipid rafts play in T cell activation?

• Groups the binding sites together, when the cell is grabbed the rafts are brought together, putting binding sites together. 

What are the stages of B cell development in the bone marrow?

1. HSC

2. CLP (common lymphoid progenitor)

3. Pre-ProB (DJ is rearranged)

4. ProB (V-DJ is rearranged)

5. PreB (VJ is rearranged)

6. Immature B cell

7. Naive after negative selection

Where do B cells go through negative selection?

In the bone marrow

What is the difference between a mature and active B cell?

A Mature B cell has been activated and completed its internal assembly and education to recognize antigens, while an active B cell has bound an antigen and received helper signals, triggering it to proliferate and differentiate

When do the DJ boxes get rearranged in B cell development?

during Pre-ProB

When do the V-DJ boxes get rearranged in B cell development?

during ProB

When do the VJ boxes get rearranged in B cell development?

during PreB

What is the Pre-ProB stage?

The earliest committed stage of B lymphocyte development in the Bone marrow, where the DJ boxes get rearranged.

What is a pre BCR?

the Bone cell receptor with a rearranged heavy chain and a surrogate light chain.