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PCB 3233 Exam 4 Study Guide Questions And Answers With 100% Correct Answers
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start of chapter 7 Define clonal expansion and how it contributes to the activation of naïve T cells. (Hint: B7, CD28, and PAPCs are all involved at this point) - Clonal expansion is the proliferation of lymphocytes to produce identical cells. This means more naïve T cells can be activated by P...

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  • August 12, 2024
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  • 2024/2025
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PCB 3233 Exam 4 Study Guide
start of chapter 7



Define clonal expansion and how it contributes to the activation of naïve T cells. (Hint: B7, CD28, and P-
APCs are all involved at this point) - Clonal expansion is the proliferation of lymphocytes to
produce identical cells. This means more naïve T cells can be activated by P-APCs.



CTLA-4 and B7:

a. What does CTLA-4 bind to? What is the result of this binding?

b. What cell is responsible for putting-up CTLA-4 on its surface?

c. Differentiate between the effects of B7 and CTLA-4 in respect to one another. Which of the two will
activate a T cell? Which of the two will limit activation? Understand this concept. - a. CTLA-4 binds
to B7 and slows down activation and limits cell proliferation.

b. CTLA-4 is found on T cells.

c. B7 activates a cell while CTLA-7 limits activation.



Regarding the initial stages of T-cell maturation, explain the direction of its migration using "subcapsular
region", "medulla", and "cortex" as references in your description. Where would you expect to find
macrophages? What about dendritic cells? - As the T-cell matures, it migrates from the
subcapsular region of the thymus to the inner cortex and to the medulla. Macrophages are found in both
the cortex and the medulla. Dendritic cells are found in the medulla.



In the thymus, what is the role of macrophages? Where are Hassal's corpuscles found? -
Macrophages remove the thymocytes that do not mature properly. Hassal's corpuscles is found in
the medulla of the thymus and it induces the development of regulatory T cells.



Evident from patient's who demonstrate DiGeorge's syndrome, the development of a functional T-cell
repertoire is crucial to an individual's health. What causes DiGeorge's syndrome? Know the chromosome
affected. Identify what is NOT being produced in this clinical condition, and what further consequences
are associated. Can DiGeorge's syndrome be cured? - DiGeorge's syndrome is caused by a deletion
in chromosome 22 where the thymus fails to develop and T cells are absent. The lack of T cells and
thymus increases susceptibility to a wide range of opportunistic infections and it resembles SCID (severe
combined immunodeficiency disease). Cannot be cured.

, The thymus is considered to be completely developed before birth. However, its deterioration results
with natural aging, indicating that the younger you are, the more active it is. Knowing this, would you
expect T-cell immunity to become defective overtime? Why or why not? What about in the case of a
thymectomy (removal of thymus); would you expect impairment then? - T-cell immunity does not
become defective over age. The thymus just does not develop as many T-cells over time. T-cells stay in
circulation for several years. T-cells do not become defective even after a thymectomy.



How does the life of a T cell differ from that of a B cell? Which lives longer and why do you think that is?
(Hint: understand what "self renewing" means in this context) - T cells are long-lived and self-
renewing. T cells are in circulation in the blood stream for several months. Self-renewing cells divide to
maintain the amount of cells.



Double-Negative (DN) thymocytes vs. Double-Positive (DP) thymocytes:

a. When/why are they called DN thymocytes?

i) What cell-surface proteins are expressed? Which are NOT being expressed?

ii) What is the importance of Notch 1 for these thymocytes?

b. When/why are they called DP thymocytes?

i) What cell-surface proteins are being expressed at this point? - a. T cells that express the αβ TCR
but do not express CD4/CD8/NK cell markers. This happens when the progenitor T cell expresses T-cell
specific adhesion molecule CD2 and other molecules but not TCR complex.

i) CD2 and CD5 are expressed. CD4 and CD8 are not expressed.

ii) Notch 1 keeps the T-cell on the T-cell path.

b. T cells that express both CD4 and CD8.

i) CD2, CD5, CD4, and CD8 are being expressed.



The two T-cell lineages: α:β and γ:δ

a. Which is considered to be the majority and which is the minority?

b. Do the loci lineages derive from a common DN or DP thymocyte precursor?

c. Which loci (α, β, γ, δ) begin their rearrangement roughly at the same time?

i) Understand what is meant by "competition" that's observed at this point, and what will be produced
as an outcome. (Hint: depends on what T-cell lineage is made, think about what the result would be if a

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