This set of Cell Biology Multiple Choice Questions & Answers (MCQs) focuses on “Immune Response – T-lymphocytes”.
1. T-cells are activated by _______________
a) autoantibodies
b) antibodies
c) fragments of antigens
d) intact antigens
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Explanation: Unlike B-cells, T-cells do not require intact antigens for activation rather small fragments of antigens. The antigen-presenting cells display fragments of antigens on their surfaces that can be recognized by the T-cell receptors.
2. The dendritic cells were discovered by _______________
a) Ralph Steinman
b) Barry Marshall
c) David Baltimore
d) Peter Medawar
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Explanation: The vital antigen presenting cells (APCs) include dendritic cells and macrophages. Dendritic cells were discovered and characterized by Ralph Steinman of the Rockefeller University in 1970s.
3. Each T-cell has a single species of T-cell receptor.
a) True
b) False
View Answer
Explanation: Like B-cells, T-cells also undergo clonal selection. T-cells contain T-cell receptors that help them recognize and bind to certain infected cells or antigenic compounds. Each T-cell has a single species of T-cell receptors.
4. The activation of T-cell by the dendritic cells is associated with __________________
a) increase in magnesium ions
b) decrease in magnesium ions
c) increase in calcium ions
d) decrease in calcium ions
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Explanation: When the antigen-presenting cells – dendritic cells display fragments of antigens on their surface in the lymph nodes, the binding with a particular T-cell receptor occurs that leads to activation of the latter. The activation is associated with a transient increase in cytosolic calcium concentration.
5. Proliferation of T-cells in response to antigen presentation is accompanied by enlargement of __________________
a) lymph nodes
b) area of infection
c) size of antibody
d) size of B-cells
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Explanation: When a fragment of antigen binds to the T-cell receptor, it results in the proliferation of a particular clone of T-cells. A T-cell can proliferate 3 to 4 times per day, accompanied by enlargement of the lymph nodes.
6. After the clearance of foreign antigen, the expanded T-cell population ________________
a) dies by apoptosis
b) increases in size
c) remains in the circulatory system
d) remains in lymph nodes
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Explanation: After the clearance of foreign antigen, the expanded T-cell population dies by apoptosis and a small population of memory T-cells remains for future contact with the same antigen.
7. T-cells secrete antibodies for eradicating the infected cells.
a) True
b) False
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Explanation: Unlike B-lymphocytes, the T-cells do not secrete antibodies for destroying the infected cells. The T-cells possess T-cell receptors on their surfaces, by which they can interact directly with the antigen-presenting cells.
8. Cytokines are ________________
a) antigens
b) proteins
c) polysaccharides
d) carbohydrates
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Explanation: Cytokines are small proteins that work at low concentrations; secreted by a wide variety of cells and include interferons (IFs), interleukins (ILs), and tumor necrosis factors (TNFs). In addition to cell-cell contact, the T-cells also mediate their interactions by cytokines.
9. Chemokines act as ___________________
a) buffers
b) receptors
c) chemoattractants
d) antibodies
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Explanation: Chemokines are a small family of cytokines that are powerful chemo-attractants that stimulate and regulate the migration of lymphocytes into the inflammation sites.
10. Perforins and granzymes are secreted by ______________________
a) Cytotoxic T lymphocytes
b) Helper T lymphocytes
c) Regulatory T lymphocytes
d) B lymphocytes
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Explanation: Cytotoxic T lymphocytes patrol the body and screen cells for abnormalities. The CTLs secrete perforins in tightly enclosed space between cells that leads to the formation of transmembrane channels through which the granzymes enter the cells and direct them to apoptosis.
11. After entering the target cells, the granzymes activate the ______________________
a) antibodies
b) chemokines
c) perforins
d) caspases
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Explanation: After entering the target cells through the perforin transmembrane channels, the granzymes (proteolytic enzymes) activate caspases that direct the cells to undergo apotosis.
12. Cytotoxic T cells are _____________
a) CD2+
b) CD4+
c) CD6+
d) CD8+
View Answer
Explanation: The cytotoxic T-cells are CD8+ because they contain a surface protein CD8 (cluster designation 8). The CTLs screen the cells of the body for any abnormalities and then function to rectify them.
13. Helper T lymphocytes possess ____________ proteins on their surface.
a) CD2
b) CD3
c) CD4
d) CD5
View Answer
Explanation: The helper T cells have CD4 proteins on their surface instead of CD8 proteins as in case of cytotoxic T cells. Helper T cells play a role in orchestrating attack against a specific pathogen.
14. Which of the following is the main target of HIV?
a) Helper T cells
b) Autoantibodies
c) Cytotoxic T cells
d) B lymphocytes
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Explanation: Helper T cells (TH) play an important role in the attack against specific antigens. The HIV attacks helper T cells which are necessary for the differentiation of B cells into antibody secreting plasma cells. When the count of TH cells in the body drops below 200 cells/μl the body becomes prone to infections.
15. Which of the following is an essential requirement for the differentiation of regulatory T cells?
a) FOXP1
b) FOXP2
c) FOXP3
d) FOXP4
View Answer
Explanation: Regulatory T lymphocytes are inhibitory cells that suppress proliferation of immune cells. They possess CD4+ and CD25+ markers on their surface. The proliferation of TReg cells require a transcription factor FOXP3.
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