This set of Immunology Multiple Choice Questions & Answers (MCQs) focuses on “T-Cell Activation and the Two-Signal Hypothesis”.
1. Where do T cell mature in human body?
a) Thymus
b) Bone marrow
c) Spleen
d) Hematopoietic tissue
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Explanation: T cells originate from hematopoietic stem cells which are found in the bone marrow. However, they mature in the thymus and hence these cells are designated as T cells. These cells play an important role in controlling and shaping immune responses.
2. Which of the following is NOT a type of T cell?
a) Cytotoxic T cell
b) Helper T cell
c) Plasma cell
d) Regulatory T cell
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Explanation: Plasma cell is a type of B cell. When B cells are activated, they differentiate into Plasma cells. These cells are lymphocytes with large amount of endoplasmic reticulum which are responsible for producing antibodies to specific antigens. They respond to signals from T cells and continue to produce antibodies with respect to that specific antigen until the infection is controlled. On the other hand, Cytotoxic T cells, Helper T cells and Regulatory T cells are types of T cells.
3. What are double-positive T cells?
a) The cells that express CD44– and CD25+
b) The cells that express CD4+ and CD8+
c) The cells that do not express CD44– and CD25+
d) The cells that do not express CD4+ and CD8+
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Explanation: The cells that express both, CD4+ and CD8+ are termed as double-positive T cells. During their expression, these cells migrate deep into the thymic cortex where they are presented with self-antigens. These double-positive T cells are responsible for the positive selection of T cells. Positive selection occurs when the double-positive T cells bind to cortical epithelial cells to carry out the interaction with MCH1 or MHC2 in order to receive vital survival signals.
4. Which cytokine is produced by Th9 cell which is a subset of helper T cell?
a) IL-4
b) IL-17
c) IL-9
d) IL-21
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Explanation: IL-9 is a pleiotropic cytokine produced by Th9 cells. It is also produced secondarily by other cells like mast cells, NK cells and Th2 cells. However, Th9 cells are considered to be main helper T cells to produce IL-9. IL-9 exerts its effects on multiple types of cells and tissues. It plays an important role in immune responses against parasites and pathogenesis of allergic diseases. It also carries out defence mechanism against helminths.
5. What is the major difference between Central memory T cells (TCM Cells) and Effector memory T cells (TEM Cells)?
a) TCM cells can express CD45RO but TEM cells lack expression of CD45RO
b) TCM cells have a high affinity to express CD44 but TEM cells lack this affinity
c) TCM cells express C-C chemokine receptor type 7 (CCR7) and L-selectin while TEM cells lack this expression
d) TCM cells express CD45RO, CD44 and CCR7 while TEM cells lack expression of all three
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Explanation: Central memory T cells (TCM cells) and Effector memory T cells (TEM cells), both can readily express CD45RO as well as CD4d) The only differentiating factor between both the cell subtypes is that TCM cells have the ability to express C-C chemokine receptor type 7 (CCR7) and L-selectin while TEM cells lack this expression. Another important differentiating factor between both cell subtypes is that TCM cells are commonly found in lymph nodes and hence they readily react to lymph node receptors while TEM cells do not react to lymph node receptors. Hence, they are found in peripheral circulation and tissues.
6. Which type of T cells recognize glycolipid antigen in adaptive immune system?
a) Natural Killer T cells (NKT cells)
b) Memory T cells
c) Regulatory T cells
d) Helper T cells
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Explanation: Natural Killer T cells (NKT cells) are different from Natural Killer cells (NK cells). NK cells help in innate immune system while NKT cells bridge the adaptive immune system with the innate immune system. NKT cells recognize glycolipid antigen in adaptive immune system. It is presented by CD1d. Once NKT cells are activated, they help in cytokine production. They also recognize and eliminate tumour cells.
7. Which of the following is NOT the role of T-box transcription factor?
a) It has the ability to activate set of genes to promote differentiation
b) It suppresses the development of opposing lineage
c) It enhances production of IFNγ
d) It helps in initiating the differentiation of Th1 cells
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Explanation: Interleukin 12 (IL-12) and interferon γ (IFNγ) are the major cytokines important in initiating the differentiation of Th1 cells. The T-box transcription factor is known as the master regulator for Th1 differentiation. It has the ability to activate set of genes to promote differentiation of Th1 cells by suppressing the development of Th2 cells. It also enhances production of IFNγ.
8. Boosting the function and quantity of T-cells is important in COVID-19 patients for recovery.
a) True
b) False
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Explanation: Boosting the function of T cells is very important for recovery of COVID-19 patients. Current studies indicate that there is a decrease in total T cells (CD4+ and CD8+) patients suffering from COVID-19. The recent hypothesis suggests that this decrease in T cells is due to increased level of cytokines like IL-10. This increase in cytokine levels can be due to chronic inflammation. This usually is the case in people above the age 60.
9. What is the major role of IL-15 with respect to T cells?
a) It helps in T cell homeostasis
b) It is the mediator of allergic inflammation
c) It helps in T follicular helper (Tfh) cell lineage
d) It helps in proliferation and survival of T cells
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Explanation: IL-15 is one of the most important cytokines which plays various roles in regulating T cell responses. It helps in proliferation of T cells and carries out mechanisms necessary for survival of T cells. IL-15 also promotes activation of CD4+ cells. It helps in survival of CD8+ cells. On the other hand, T cell homeostasis is carried out by IL-b) IL-13 acts as the mediator of allergic inflammation while IL-6 helps in T follicular helper cell lineage. It is also considered as an important cytokine as it provides protection from pathogens during an infection.
10. Who discovered T-cell receptor (TCR)?
a) Timothy Mosmann
b) Christopher E. Rudd
c) Philippa Marrack
d) Shimon Sakaguchi
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Explanation: Philippa Marrack (Immunologist) contributed to Immunology by studying about T cell receptor. She found out that T cell reacts with fragments of infection bound to MHC proteins in human body. She has also studied and carried out various experiments on the work of vaccines in order to find out the ability of T cells to attack invader molecules. On the other hand, Timothy Mosmann created a model of Th1 vs Th2 to find out the functions of helper T cells. Christopher E. Rudd discovered biochemical initiators of T-cell activation and Shimon Sakaguchi discovered regulatory T cells.
11. What is the role of first signal during the activation of T cells?
a) Induction of surface receptors on Antigen-Presenting Cells (APCs)
b) Binding of T cell receptor to cognate peptide presented on MHC II
c) Binding of T cell receptor to MCH I peptide
d) Carrying out mechanism to express CD28
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Explanation: Activation of T-cell is completed by two important signals. 1) The major role of first signal is that it helps in binding of T cell receptor (on CD4+ helper T cells and CD8+ cytotoxic T cells) to its cognate peptide present in MHC II structure on an Antigen-Presenting Cell (APC). This binding triggers the initial activation of T cell. CD4 and CD8 then bind to this MHC II molecule in order to stabilize the whole structure. This entire mechanism sets the response in motion.
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