This set of Immunology Multiple Choice Questions & Answers (MCQs) focuses on “T-Cell Development”.
1. During positive selection of T cells, what molecules do they present?
a) Short pieces of proteins
b) Granules
c) Fragments of DNA
d) Survival signals
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Explanation: Positive selection of T cells is very necessary as they have to bind to the MHC complexes in order to induce apoptosis in the infected cells. This process involves the T cells (that are present in the thymus) to present short pieces of proteins which are called as peptides in order to initiate the binding of T cells to MHC complexes.
2. If T cell receptor successfully bind to MHC molecules, they undergo apoptosis.
a) True
b) False
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Explanation: In order to kill the infected cell or induce apoptosis in the infected cell, it is necessary for the receptor of T cell (TCR) to bind to the MHC molecules. If this binding is successful, the T cell receives surviving signals and hence, it is positively selected to induce cell death in the infected cell. However, if T cell receptor fails to bind to the MHC molecule, the TCR of T cell itself undergoes death (or apoptosis).
3. Which mechanism takes place within the T cells to produce T cell clones?
a) Positive selection
b) Negative selection
c) Somatic recombination
d) Thymic development
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Explanation: When the immature T cells enter the thymus, they undergo various developmental stages to form mature T cells. The first step for this development takes place by somatic recombination. This mechanism initiates the developmental process to generate T cell clones which express the T cell receptors.
4. What do the T cells depend on during negative selection?
a) Mature T cell receptors
b) T cells of the thymus
c) T cells of the bone marrow
d) B cells of the bone marrow
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Explanation: Negative selection refers to the fact that T cells should prevent recognizing and attacking their own cells. This selection of T cells occurs in the thymus due to which it is obvious that these cells will depend on the other T cells in the thymus itself. Their dependency is very strange but at the same time important enough for presenting self-peptides on MHC molecules so that they attack the invading pathogenic cells together.
5. Recognition of self-peptides is important for which subtype of T cells?
a) Treg cells
b) CD4+ T cells
c) αβ T cells
d) Cytotoxic T cells
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Explanation: Initially self-peptides are present on the MHC molecules. These MHC molecules are present on antigen presenting cells (APCs) which are associated with the thymus. These self-peptides are very important in determining the fate of the αβ T cells. However, recognition of self-peptides can even prove harmful in cases where they start attacking their own cells.
6. What does cTEC stand for?
a) Cortical thymic epithelial cells
b) Cortical thymic endothelial cells
c) Central thymic epithelial cells
d) Central thymic endothelial cells
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Explanation: Cortical thymic epithelial cells (cTECs) are one of the most important cells to play a role in T cell selection. They interact with double negative as well as double positive thymocytes. They also form multi-cellular complexes by selecting almost about 20 thymocytes. In other words, they surround the selected thymocytes and these thymocytes are called as thymic nurse cells.
7. What are proteasomes that incorporate β5t called?
a) Thymosomes
b) Proteases
c) Thymoproteasomes
d) Lysosomal proteases
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Explanation: Proteosomes are the molecules that generate peptides. They carry out the catalytic activities and this is mediated by β1, β2 and β5. Proteasomes that incorporate β5t are called as thymoproteasomes while proteosomes that incorporate β5i are called as immunoproteasome. The study of proteosome was first studied in mice.
8. Which protein reduces expression of Runx3 during positive selection?
a) ThPOK
b) ThRUNx
c) ThPR
d) ThPOK and ThRUNx
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Explanation: Positive selection of T cells is very important as it determines the T cell to develop into CD8+ or CD4+ T cell. This selection allows the TCR to bind to MHC class II in order to send signals for inducing the expression of ThPOK. This protein further reduces the expression of Runx3 which is responsible for driving CD8 expression.
9. What does AIRE stand for?
a) Autoimmune regulation of endothelial cells
b) Autoimmune regulation
c) Autoimmune regulator
d) Autoimmunology of regulatory endothelial cells
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Explanation: AIRE stands for autoimmune regulator. This plays a major role in selection of T cells. one of its roles is in the thymus to induce the expression of various proteins which are not primarily associated with the thymic cells. In this way AIRE helps the developing T cells to expose to the unknown peptide-MHC complexes which are not in association with the regularly active T cells.
10. Where do the survived positively selected T cells first migrate to?
a) Cortico-medullary junction
b) Thymus
c) Bone marrow
d) Medullary region of thymus
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Explanation: T cell development is very important and it undergoes two main developmental processes namely positive and negative selection. Positive selection of T cell involves development of T cell into CD8+ or CD4+ T cells. Once these cells have undergone positive selection, they further proliferate into the cortico-medullary junction of the thymus to undergo negative selection. In this junction, these cells encounter macrophages and dendritic cells.
Sanfoundry Global Education & Learning Series – Immunology.
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