PCB 4233 IMMUNOLOGY FINAL EXAM QUESTONS
AND ANSWERS
What ligand determines whether bone marrow stem cells will differentiated in B cells or
T cells? - Answers -Notch, Notch positive cells become T cells while Notch negative
cells become B cells
Bone marrow stem cells exposed to Notch will become - Answers -T cells
Where are Notch ligands found? - Answers -The thymic epithelium
Which process is responsible for driving CD4 or CD8 expression? - Answers -Positive
selection
Describe positive selection - Answers -MHC is presented to naive T cells. T cells which
bind well to MHC are positively selected for. If there is weak binding, the cell undergoes
apoptosis (programmed cell death). If the cell binds strongly to MHCII, the cell
upregulates ThPOK and downregulates Runx3 to become a CD4+ T cell. Otherwise, the
cell becomes a CD8+ T cell
ThPOK+Runx3- - Answers -CD4+ T cell
ThPOK-Runx3+ - Answers -CD8+ T cell
Describe negative selection - Answers -If a T cell binds too strongly to MHC, the cell
undergoes apoptosis
Why is negative selection important? - Answers -It is a measure to protect against
autoimmunity
How does negative selection ensure T cells don't respond inappropriately to peptide-
MHC complexes not found in the thymus? - Answers -AIRE is a protein that induces
expression of proteins not found in the thymus, ex. lung protein, to ensure that T cells
do not react to proteins found throughout the body after undergoing negative selection
How do T cells move through the thymus? - Answers -1. Arrive to thymus via
corticomedullary junction
2. Differentiate into T cells in thymic epithelium
3. Move into thymic cortex where they proliferate and express TCR
4. Selection process
5. Move to thymic medulla
6. Leave via corticomedullary junction
What is the role of Bcl-2? - Answers -Prevents apoptosis by inhibiting Bax and Bak
, What is the function of Bax and Bak? - Answers -Open mitochondrial membrane,
releasing cytochrome C, triggering apoptosis
What is the function of Fas? - Answers -Induces apoptosis
How does the signal from an antigen influence T cell survival? - Answers -Antigen
signal prevents apoptosis by upregulating Bcl-2, without a signal from antigen, T cells
downregulate Bcl-2, leading to apoptosis as a protection measure against autoimmunity
Where do lymphocytes reach maturity? - Answers -Primary organs
ex. bone marrow, thymus
Where do mature lymphocytes interact with antigen? - Answers -Secondary organs
ex. lymph nodes, spleen, tonsils
What does the cortex of the thymus contain? - Answers -immature T-lymphocytes
What does the medulla of the thymus contain? - Answers -mature T-lymphocytes that
are immunocompetent (passed negative selection)
What is the purpose of lymph? - Answers -To carry lymphocytes and antigens from
body to lymphoid tissues where lymphocytes can recognize antigen and become
activated
Describe antigen migration in lymph nodes - Answers -1. Antigen gets trapped in
paracortex
2. DCs internalize antigen
3. DCs present antigen on MHCII to CD4+ T cells
Describe antigen migration in the spleen - Answers -1. Antigen enters splenic artery
2. DCs trap antigen in the marginal zone
3. DCs migrate to PALS
4. T cell activation
A virus passes by a T cell. How does it respond? - Answers -The T cell does not
respond, T cells require activation via antigen presentation by APCs (antigen presenting
cells)
What are the APCs (antigen presenting cells) that have been identified by
immunologists so far? - Answers -1. B cells
2. dendritic cells
3. macrophages
AND ANSWERS
What ligand determines whether bone marrow stem cells will differentiated in B cells or
T cells? - Answers -Notch, Notch positive cells become T cells while Notch negative
cells become B cells
Bone marrow stem cells exposed to Notch will become - Answers -T cells
Where are Notch ligands found? - Answers -The thymic epithelium
Which process is responsible for driving CD4 or CD8 expression? - Answers -Positive
selection
Describe positive selection - Answers -MHC is presented to naive T cells. T cells which
bind well to MHC are positively selected for. If there is weak binding, the cell undergoes
apoptosis (programmed cell death). If the cell binds strongly to MHCII, the cell
upregulates ThPOK and downregulates Runx3 to become a CD4+ T cell. Otherwise, the
cell becomes a CD8+ T cell
ThPOK+Runx3- - Answers -CD4+ T cell
ThPOK-Runx3+ - Answers -CD8+ T cell
Describe negative selection - Answers -If a T cell binds too strongly to MHC, the cell
undergoes apoptosis
Why is negative selection important? - Answers -It is a measure to protect against
autoimmunity
How does negative selection ensure T cells don't respond inappropriately to peptide-
MHC complexes not found in the thymus? - Answers -AIRE is a protein that induces
expression of proteins not found in the thymus, ex. lung protein, to ensure that T cells
do not react to proteins found throughout the body after undergoing negative selection
How do T cells move through the thymus? - Answers -1. Arrive to thymus via
corticomedullary junction
2. Differentiate into T cells in thymic epithelium
3. Move into thymic cortex where they proliferate and express TCR
4. Selection process
5. Move to thymic medulla
6. Leave via corticomedullary junction
What is the role of Bcl-2? - Answers -Prevents apoptosis by inhibiting Bax and Bak
, What is the function of Bax and Bak? - Answers -Open mitochondrial membrane,
releasing cytochrome C, triggering apoptosis
What is the function of Fas? - Answers -Induces apoptosis
How does the signal from an antigen influence T cell survival? - Answers -Antigen
signal prevents apoptosis by upregulating Bcl-2, without a signal from antigen, T cells
downregulate Bcl-2, leading to apoptosis as a protection measure against autoimmunity
Where do lymphocytes reach maturity? - Answers -Primary organs
ex. bone marrow, thymus
Where do mature lymphocytes interact with antigen? - Answers -Secondary organs
ex. lymph nodes, spleen, tonsils
What does the cortex of the thymus contain? - Answers -immature T-lymphocytes
What does the medulla of the thymus contain? - Answers -mature T-lymphocytes that
are immunocompetent (passed negative selection)
What is the purpose of lymph? - Answers -To carry lymphocytes and antigens from
body to lymphoid tissues where lymphocytes can recognize antigen and become
activated
Describe antigen migration in lymph nodes - Answers -1. Antigen gets trapped in
paracortex
2. DCs internalize antigen
3. DCs present antigen on MHCII to CD4+ T cells
Describe antigen migration in the spleen - Answers -1. Antigen enters splenic artery
2. DCs trap antigen in the marginal zone
3. DCs migrate to PALS
4. T cell activation
A virus passes by a T cell. How does it respond? - Answers -The T cell does not
respond, T cells require activation via antigen presentation by APCs (antigen presenting
cells)
What are the APCs (antigen presenting cells) that have been identified by
immunologists so far? - Answers -1. B cells
2. dendritic cells
3. macrophages
