ANSWERS|LATEST
start of chapter 7
Where does T-cell maturation take place? - ANSWER T-cell maturation takes place in
the thymus
Be able to understand some similarities and differences between B cell and T cell
development.
a. Examples: Where do they derive? What cellular mechanisms or processes are shared
between the two? What comprises their cell lineages? - ANSWER Both B-cells and T-
cells derive from the bone marrow stem cells but the T-cell moves to the thymus to mature
while the B-cell stays in the bone marrow. Both undergo gene rearrangement which
produces antigen receptors. T cells have two lineages.
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? - ANSWER 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? -
ANSWER 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.
1
, 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? - ANSWER 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? - ANSWER 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) -
ANSWER 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? - ANSWER 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.
2
start of chapter 7
Where does T-cell maturation take place? - ANSWER T-cell maturation takes place in
the thymus
Be able to understand some similarities and differences between B cell and T cell
development.
a. Examples: Where do they derive? What cellular mechanisms or processes are shared
between the two? What comprises their cell lineages? - ANSWER Both B-cells and T-
cells derive from the bone marrow stem cells but the T-cell moves to the thymus to mature
while the B-cell stays in the bone marrow. Both undergo gene rearrangement which
produces antigen receptors. T cells have two lineages.
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? - ANSWER 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? -
ANSWER 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.
1
, 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? - ANSWER 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? - ANSWER 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) -
ANSWER 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? - ANSWER 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.
2
