This set of Immunology Multiple Choice Questions & Answers (MCQs) focuses on “Cytotoxic T-cells”.
1. Which cells produce cytokines to trigger Cytotoxic T lymphocytes (CTLs)?
a) CD4+
b) CD8+
c) CD28+
d) CD69+
View Answer
Explanation: CTLs play an important role in destroying the cell that expresses peptide-MHC1 complex because this complex results in protein degradation. This destruction takes place only if CTLs are activated. As a result, CD4+ cells produce cytokines to trigger CTLs in order to activate them to scan for protein alterations or differences made by the complex. CTLs also provide protection against spontaneous malignant tumours, as they have the ability to detect quantitative and qualitative antigenic differences in transformed cells. These differences result in irregular protein performance inside the cell.
2. Secretion of exosomes by fully activated Cytotoxic T cells is mediated by which cytokine?
a) IL-15
b) IL-12
c) IL-2
d) IL-5
View Answer
Explanation: Fully activated Cytotoxic T cells can secrete exosomes with the help of cytokine IL-12. This secretion results in strong affinity cytotoxic T cell peptides. Exosomes secreted by these fully activated cells strengthens the weak cytotoxic T cells that have low affinity peptides. Exosomes also enhance the activation of these weak cells. IL-12 plays a very important role as it acts as a mediator in order to carry out this mechanism. It also induces self-reactivity within cytotoxic T cells.
3. Which of the following is NOT a sequential signal for the generation of effector Cytotoxic T lymphocytes?
a) TCR ligation
b) Transmission of co-stimulatory signals
c) IL-2 mediated signalling
d) Internalization of TCR
View Answer
Explanation: Generation of Effector CTLs occurs in three sequential signals – 1) TCR ligation which helps in activation of CTLs and is responsible for producing immune responses. 2) Transmission of co-stimulatory signals. These signals provide activating signals to T cells from TCR in order to follow the functional track of interaction with antigen and MHC molecules resulting in differentiation of T cells. 3) Signals mediated by cytokine IL-2 that works as a growth regulator of CTLs and supports proliferative expansion of CTLs.
4. Which cell works as a dual receptor in CTLs?
a) CD4
b) CD8
c) CD13
d) CD4+
View Answer
Explanation: In CTLs the CD8 molecule has two functions as a receptor 1) recognizing the ligand. (MHC molecules OR non-antigen specific ligands are served for the TCR) 2) initiating signal transduction (signal transduction in CTLs can be initiated by interactions of CD8 and MHC class 1) Due to double functionality of CD8 it is also referred to as a dual receptor.
5. Cytotoxic T-lymphocyte-associated antigen 4 is expressed by activated effector T cells and it represses the proliferation of T cell.
a) True
b) False
View Answer
Explanation: Cytotoxic T-lymphocyte-associated antigen 4 is also denoted as CTLA-4. It is a glycoprotein expressed by activated effector T cells. It plays a major role in repression of T cell proliferation and helps in enhancing the progressive ability of cell cycle. CTLA-4 also has some inhibitory functions which might produce irregular functioning of T cells. The most important clinical use of CTLA-4 is that it is targeted by antibodies therapeutically in human malignancies in order to block its inhibitory effects.
6. Who demonstrated priming of Cytotoxic T lymphocytes responses against tumour antigen?
a) Edward Jenner
b) Ernst Haeckel
c) Paul Ehrlich
d) Schoenberger
View Answer
Explanation: Schoenberger and his colleagues demonstrated experiments to prove that priming of CTL responses against tumour antigen can be dependent on CD40 signalling. They suggested that Th cells also play an important role in generation of CTLs. They showed that signalling through CD40 (that is expressed on dendritic cells) is one of the important sources for Th-cell dependent preparation of antigen presenting cells for CTL generation. They proved it through drawing a conclusion that CD40 could easily cross-link with antibodies and they did not need T cell interactions to proceed the generation of CTLs.
7. Cytotoxic T cells kill target cells by interaction of which two cytokines?
a) IFN-γ and TNF-α
b) IFN- and IL-1
c) TNF-α and IL-2
d) IL-13 and IL-2
View Answer
Explanation: Cytotoxic T cells can kill target cells by two ways – 1) direct cell-cell contact between effector and target cells. 2) by action of cytokines – IFN-γ and TNF-α (Tumour necrosis factor). These cytokines are produced and secreted as long as T cell receptor stimulation continues. TNF-α engages its receptor on the target cell and triggers the caspase cascade, leading to target-cell apoptosis and IFN-γ induces transcriptional activation of the MHC class I antigen presentation pathway.
8. Cytotoxic T cells play an important role in pathogenesis of which autoimmune disease?
a) Diabetes melitus
b) Vitiligo
c) Systemic sclerosis
d) Paraneoplastic pemphigus
View Answer
Explanation: Vitiligo is a common hypo-pigmentary disorder that affects approximately 2% of the world population. Vitiligo is a disease in which destruction of melanocytes takes place and this result in the loss of skin pigmentation. Cytotoxic T cells, specifically CD8 cells play a very important role in pathogenesis of Vitiligo. Melanocyte-specific CD8 T cells are present in peripheral blood and skin lesions. These cells have a cytolytic ability as they take destructive actions against melanocytes.
9. Which of the following cytokine is not released by Cytotoxic CD8+ T cells in order to carry out host defence mechanisms?
a) IFN-γ
b) TNF-α
c) TGF-β
d) TNF-β
View Answer
Explanation: Three of the most important cytokines released by cytotoxic CD8+ T cells are IFN-γ, TNF-α and TNF-β. IFN-γ directly inhibits viral replication as well as it enhances the expression of MHC class I and the molecules which are involved in peptide loading of the newly synthesized MHC class I proteins in infected cells. It also helps in activating macrophages by recruiting them to sites of infection both as effector cells and as antigen-presenting cells. TNF-α and TNF-β combine and interact with IFN-γ in order to activate macrophages. They also help in killing some target cells.
10. Which cytotoxic T lymphocyte(s) have become important considerations in the design of cancer vaccine-based clinical trials?
a) MHC-restricted CD8+ and CD4+ CTLs
b) MHC-restricted CD8+ CTLs
c) MHC-restricted CD4+ CTLs
d) MHC-linked CD8+ and CD4+ CTLs
View Answer
Explanation: Major histocompatibility complex-restricted CD8+ and CD4+ CTLs have play very crucial roles in host defence mechanisms against human malignancies. They are highly considered in cancer vaccine-based clinical trials. In various experimental systems, it has also become evident that neoplastic cells may avoid cell-mediated immune responses to effector cells and interactions with cell surface in order to kill target cells. This can affect the regulation of metastatic processes. In such a case, MHC-restricted CD8+ and CD4+ CTLs carry out the defence mechanism to regulate metastasis.
Sanfoundry Global Education & Learning Series – Immunology.
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