PCB4233 IMMUNOLOGY FINAL EXAM
QUESTIONS AND ANSWERS WITH VERIFIED
SOLUTIONS (GRADED A+) | NEW 2026/27
What ligand determines whether bone marrow stem cells will differentiated in B
cells or T cells?
ANSWERS The Notch ligand. Cells that receive Notch signaling are directed to
become T cells, while those that do not (Notch negative) differentiate into B cells.
Bone marrow stem cells exposed to Notch will become -
ANSWERS T cells.
Where are Notch ligands found?
ANSWERS They are expressed by the thymic epithelium.
Which process is responsible for driving CD4 or CD8 expression?
ANSWERS Positive selection.
Describe positive selection -
ANSWERS This occurs when MHC molecules are presented to naive T cells. T
cells that successfully bind to the MHC are "positively selected" to survive; if
binding is too weak, the cell undergoes apoptosis. If the cell binds strongly to MHC
II, it upregulates ThPOK and downregulates Runx3 to become a CD4+ T cell. If it
binds to MHC I, it becomes a CD8+ T cell.
ThPOK+ Runx3- -
,ANSWERS This profile results in a CD4+ T cell (Helper T cell).
ThPOK- Runx3+ -
ANSWERS This profile results in a CD8+ T cell (Cytotoxic T cell).
Describe negative selection -
ANSWERS This is the process where T cells that bind too strongly to self-
MHC/peptide complexes are induced to undergo apoptosis to prevent them from
attacking the body's own tissues.
Why is negative selection important?
ANSWERS it is a critical safety mechanism that protects the body against
autoimmunity.
How does negative selection ensure T cells don't respond inappropriately to
peptide-MHC complexes not found in the thymus?
ANSWERS The AIRE (Autoimmune Regulator) protein induces the expression
of "tissue-specific" proteins (like lung or insulin proteins) within the thymus. This
allows the thymus to test T cells against proteins found throughout the rest of the
body before they are released.
How do T cells move through the thymus?
ANSWERS 1. Precursors arrive at the thymus via the corticomedullary
junction.
2. They begin differentiation within the thymic epithelium.
3. They migrate to the thymic cortex to proliferate and express their T-cell
receptors (TCR).
, 4. They undergo the selection process (positive and negative).
5. Surviving cells move into the thymic medulla.
6. Mature T cells exit the thymus back through the corticomedullary junction.
What is the role of Bcl-2?
ANSWERS It acts as a survival signal that prevents apoptosis by inhibiting the
pro-apoptotic proteins Bax and Bak.
What is the function of Bax and Bak?
ANSWERS These proteins promote cell death by opening the mitochondrial
membrane, which releases cytochrome C and triggers the apoptotic cascade.
What is the function of Fas?
ANSWERS It is a "death receptor" that, when activated, induces apoptosis in
the cell.
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
QUESTIONS AND ANSWERS WITH VERIFIED
SOLUTIONS (GRADED A+) | NEW 2026/27
What ligand determines whether bone marrow stem cells will differentiated in B
cells or T cells?
ANSWERS The Notch ligand. Cells that receive Notch signaling are directed to
become T cells, while those that do not (Notch negative) differentiate into B cells.
Bone marrow stem cells exposed to Notch will become -
ANSWERS T cells.
Where are Notch ligands found?
ANSWERS They are expressed by the thymic epithelium.
Which process is responsible for driving CD4 or CD8 expression?
ANSWERS Positive selection.
Describe positive selection -
ANSWERS This occurs when MHC molecules are presented to naive T cells. T
cells that successfully bind to the MHC are "positively selected" to survive; if
binding is too weak, the cell undergoes apoptosis. If the cell binds strongly to MHC
II, it upregulates ThPOK and downregulates Runx3 to become a CD4+ T cell. If it
binds to MHC I, it becomes a CD8+ T cell.
ThPOK+ Runx3- -
,ANSWERS This profile results in a CD4+ T cell (Helper T cell).
ThPOK- Runx3+ -
ANSWERS This profile results in a CD8+ T cell (Cytotoxic T cell).
Describe negative selection -
ANSWERS This is the process where T cells that bind too strongly to self-
MHC/peptide complexes are induced to undergo apoptosis to prevent them from
attacking the body's own tissues.
Why is negative selection important?
ANSWERS it is a critical safety mechanism that protects the body against
autoimmunity.
How does negative selection ensure T cells don't respond inappropriately to
peptide-MHC complexes not found in the thymus?
ANSWERS The AIRE (Autoimmune Regulator) protein induces the expression
of "tissue-specific" proteins (like lung or insulin proteins) within the thymus. This
allows the thymus to test T cells against proteins found throughout the rest of the
body before they are released.
How do T cells move through the thymus?
ANSWERS 1. Precursors arrive at the thymus via the corticomedullary
junction.
2. They begin differentiation within the thymic epithelium.
3. They migrate to the thymic cortex to proliferate and express their T-cell
receptors (TCR).
, 4. They undergo the selection process (positive and negative).
5. Surviving cells move into the thymic medulla.
6. Mature T cells exit the thymus back through the corticomedullary junction.
What is the role of Bcl-2?
ANSWERS It acts as a survival signal that prevents apoptosis by inhibiting the
pro-apoptotic proteins Bax and Bak.
What is the function of Bax and Bak?
ANSWERS These proteins promote cell death by opening the mitochondrial
membrane, which releases cytochrome C and triggers the apoptotic cascade.
What is the function of Fas?
ANSWERS It is a "death receptor" that, when activated, induces apoptosis in
the cell.
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
