PCB 3233
PCB 3233 Immunology, Exam 4
Questions with Correct Answers 2026
2 Distinct T-Cell Lineages
a:b & g:d (α:β & γ:δ)
Positive Selection
leads to the death of immature T-cells having receptors that do not interact with
any self-MHC I or II (takes place prior to negative selection)
Negative Selection
induces death of those immature T-cells that are autoreactive (also happens with
B-cells)
Majority Lineage Type of T-Cell
a:b (α:β 95%)
Minority Lineage Type of T-Cell
g:d (γ:δ 5%)
What is another word for immature T-cell?
thymocyte
What is the epithelial cell network that thymocytes are embedded in called?
thymic stroma
What takes place in the Thymus Cortex?
most of T-cell maturation (except negative selection)
What takes place in the Thymus Medulla?
negative selection of T-cells
What do macrophages in the cortex and medulla do?
remove thymocytes that fail to mature properly
What are Hassall's corpuscles?
PCB 3233
,PCB 3233
a feature of the medulla; site of cell destruction
What is DiGeorge syndrome?
deletion of chromosome 22; thymus fails to develop
Progenitor T-Cell
lack the cell surface glycoproteins (have CD34 surface glycoprotein of stem cells),
germline configuration
Double Negative Thymocyte
at the start of gene rearrangement; no CD4 or CD8
Double Positive Thymocyte
after rearrangement; expresses both CD4 and CD8
Single Positive Thymocyte
after positive selection; expresses CD4 or CD8
IL-7 Receptor
essential for binding IL-7 secreted by thymic stromal cells; helps tell the cell what
to do next
Notch-1
at all stages of maturation in the thymus signals are sent to this receptor to drive
the T-cell in their differentiation
How many chances (per chromosome) does the B-chain have to rearrange
productivly?
2
What does a successful rearrangement of the B-chain induce?
expression of CD4 and CD8
Allelic Exclusion of B-chain
proliferation initiated by signaling is repressed
What signals are repressed in allelic exclusion of the B-chain?
pre-TCR, RAG-1, RAG-2
PCB 3233
, PCB 3233
When does rearrangement of the a-chain occur?
after the double-positive cells stop dividing
Will most developing T-cell be able to make a productive a-chain rearrangement?
yes
What happens after the first rearrangement between V and J segments on the a-
chain?
d (δ) segment is deleted
What is the first checkpoint of a:b (α:β) chain rearrangement?
once a b-chain is produced it is sent to the ER to make sure it can bind to the
surrogate a-chain (pTα)
What is the second checkpoint of a:b (α:β) chain rearrangement?
once an a-chain is made it is sent to the ER to make sure it can bind to the b-chain
How many MHC molecules does an individual express?
12 (6 MHC-I and 6 MHC-II)
What percentage of a:b (α:β) TCRs will pass positive selection?
1-2%
Can molecules fail positive selection for recognizing too strongly?
yes
Can molecules fail positive selection for recognizing too weakly?
yes
Where does positive selection take place?
cortex of thymus
Which region codes for CDR1 and CDR2?
V region
What recognizes MHC in positive selection?
CDR1 and CDR2
PCB 3233
PCB 3233 Immunology, Exam 4
Questions with Correct Answers 2026
2 Distinct T-Cell Lineages
a:b & g:d (α:β & γ:δ)
Positive Selection
leads to the death of immature T-cells having receptors that do not interact with
any self-MHC I or II (takes place prior to negative selection)
Negative Selection
induces death of those immature T-cells that are autoreactive (also happens with
B-cells)
Majority Lineage Type of T-Cell
a:b (α:β 95%)
Minority Lineage Type of T-Cell
g:d (γ:δ 5%)
What is another word for immature T-cell?
thymocyte
What is the epithelial cell network that thymocytes are embedded in called?
thymic stroma
What takes place in the Thymus Cortex?
most of T-cell maturation (except negative selection)
What takes place in the Thymus Medulla?
negative selection of T-cells
What do macrophages in the cortex and medulla do?
remove thymocytes that fail to mature properly
What are Hassall's corpuscles?
PCB 3233
,PCB 3233
a feature of the medulla; site of cell destruction
What is DiGeorge syndrome?
deletion of chromosome 22; thymus fails to develop
Progenitor T-Cell
lack the cell surface glycoproteins (have CD34 surface glycoprotein of stem cells),
germline configuration
Double Negative Thymocyte
at the start of gene rearrangement; no CD4 or CD8
Double Positive Thymocyte
after rearrangement; expresses both CD4 and CD8
Single Positive Thymocyte
after positive selection; expresses CD4 or CD8
IL-7 Receptor
essential for binding IL-7 secreted by thymic stromal cells; helps tell the cell what
to do next
Notch-1
at all stages of maturation in the thymus signals are sent to this receptor to drive
the T-cell in their differentiation
How many chances (per chromosome) does the B-chain have to rearrange
productivly?
2
What does a successful rearrangement of the B-chain induce?
expression of CD4 and CD8
Allelic Exclusion of B-chain
proliferation initiated by signaling is repressed
What signals are repressed in allelic exclusion of the B-chain?
pre-TCR, RAG-1, RAG-2
PCB 3233
, PCB 3233
When does rearrangement of the a-chain occur?
after the double-positive cells stop dividing
Will most developing T-cell be able to make a productive a-chain rearrangement?
yes
What happens after the first rearrangement between V and J segments on the a-
chain?
d (δ) segment is deleted
What is the first checkpoint of a:b (α:β) chain rearrangement?
once a b-chain is produced it is sent to the ER to make sure it can bind to the
surrogate a-chain (pTα)
What is the second checkpoint of a:b (α:β) chain rearrangement?
once an a-chain is made it is sent to the ER to make sure it can bind to the b-chain
How many MHC molecules does an individual express?
12 (6 MHC-I and 6 MHC-II)
What percentage of a:b (α:β) TCRs will pass positive selection?
1-2%
Can molecules fail positive selection for recognizing too strongly?
yes
Can molecules fail positive selection for recognizing too weakly?
yes
Where does positive selection take place?
cortex of thymus
Which region codes for CDR1 and CDR2?
V region
What recognizes MHC in positive selection?
CDR1 and CDR2
PCB 3233
