This set of Immunology Multiple Choice Questions & Answers (MCQs) focuses on “Cell Mediated Effector Responses – Natural Killer Cells”.
1. The MHC class I specific to Natural Killer (NK) cells include which inhibitory receptors ONLY in mice?
a) Killer cell immunoglobulin-like receptors (KIRs)
b) Lectin-like Ly49 dimers
c) Lectin-like CD94-NKG2A heterodimers
d) B and T lymphocyte attenuator (BTLA)
View Answer
Explanation: NK cells express MHC class I–specific receptors and have high signalling affinity to MHC class I-rich hematopoietic cells. However, they lose inhibitory signals when they encounter MHC class I–deficient hematopoietic cells. In such cases, NK cells have the ability to recognize their lost signals on hematopoietic cells. MHC class I specific to NK cells include Lectin-like Ly49 dimer as inhibitory receptor in mice. On the other hand, KIRs (Killer cells immunoglobulin-like receptors are present in humans and Lectin-like CD94-NKG2A heterodimers are present in both, humans as well as mice.
2. Which of the following subsets of NK cells are present in humans?
a) CD46dim and CD64bright
b) CD36dim and CD63bright
c) CD26dim and CD62bright
d) CD65dim and CD56bright
View Answer
Explanation: In humans, NK cells are divided into 2 NK subsets: CD65dim and CD56bright. These two subsets differ in various properties and functions. CD56dim NK cells are cytotoxic and produce IFN-γ on interaction with tumour cells in vitro. They have the ability to express perforin. On the other hand, CD56bright lack the ability to express perforin. However, they produce IFN-γ on interaction with cytokines like IL-12 and IL-15.
3. Which of the following is NOT a potent activator of NK cell effector function?
a) Type 2 IFN
b) IL-12
c) IL-15
d) Type 1 IFN
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Explanation: Type 1 IFN, IL-12, IL-15 as well as IL-18 are the potent activators of NK cell effector function. It is also well known that IL-2 promotes NK cell proliferation, cytotoxicity and cytokine secretion. IL-15 helps in proliferation and differentiation of NK cells and IL-18 control uterine NK cells. They also enhance innate immunity. Type 1 IFN promotes expansion of NK cells during viral infection and also protects them.
4. NK cells act as regulatory cells to influence the actions of dendritic cells.
a) True
b) False
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Explanation: NK cells interact with Dendritic cells (DCs) in peripheral tissues and lymphoid organs. NK cells kill immature dendritic cells in humans as well as in mice in order to enhance and influence DC homeostasis. They also limit the efficiency of DC-based vaccination. Along with regulation of DCs, NK cells also influence the action of endothelial cells, T and B cells by taking the role of regulatory cells.
5. VLA-4, CD62L and CX3CR1 receptors expressed on NK cells promote adherence to which of the following cells?
a) Memory T cells
b) Endothelial cells
c) Cytotoxic T cells
d) B cells
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Explanation: Endothelial cells are primary targets of immunologic attacks. Their injury can lead to organ dysfunction and vasculopathy. In order to promote commitment to these cells, 3 receptors namely VLA-4, CD62L as well as CX3CL1 come in action. NK cells eliminate these targeted and injured endothelial cells by killing them. This suggests that NK cells are involved in pathogenesis of vascular injury.
6. During which of the following infections, subsets of NK cells contribute to liver inflammation?
a) Human CMV infection
b) Arthritis
c) Sarcoidosis
d) Chronic hepatitis B virus
View Answer
Explanation: NK cells act as mediators of innate immunopathology. In patients suffering from chronic hepatitis B virus infection, subsets of NK cells have important role in liver inflammation by inducing hepatocyte death through TRAIL (TNF-related apoptosis inducing ligand)-dependent mechanism.
7. NK cells belong to which type of immune system?
a) Adaptive immune system
b) Innate immune system
c) Adaptive and Innate immune systems
d) Active Immune system
View Answer
Explanation: Natural killer cells (also abbreviated as NK cells) belong to the innate immune system. Innate immunity is the inborn ability of the cells to fight against infections. Hence, NK cells by the name itself help in killing the infection causing agents or cells. These cells are also important in regulating the functions of various other cells; hence they are also called as regulatory cells. NK cells improve hematopoietic cell functioning. They also play crucial role in organ transplantation and autoimmune disorders.
8. Which receptor is phosphorylated in order to trigger activation of NK cells?
a) T cell receptor (TCR)
b) B cell receptor (BCR)
c) Pattern Recognition Receptor (PRR)
d) Immunoreceptor tyrosine-based activation motif (ITAM)
View Answer
Explanation: The complete process of activating NK cells require not only MHC class I molecules but also some of the activating receptors. One such receptor is Immunoreceptor tyrosine-based activation motif (commonly designated as ITAM). ITAM produces the most activating receptor signals for NK cell activation. In order to produce these activating signals, there must be an interaction of ITAM with the specific ligand to form receptor-ligand complex. This complex formation leads to phosphorylation of ITAM and hence, activation of NK cells is triggered.
9. Cytotoxic immune response of NK cells leads to the release of which cytotoxic molecules?
a) Perforin and Lectins
b) Antimicrobial-peptides and quinoid intermediates
c) Perforin and Granzyme
d) Granzyme and Lectins
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Explanation: The cytotoxic immune response of NK cells leads to the release of perforins and granzyme. This process is termed as degranulation. Cytotoxic response of NK cells starts by formation of synapse between target cells and NK cells. As soon as synapse formation takes place, secretory lysosomes are polarized towards the synapse. As and when they are directed towards the synapse, they get docked or tied up with Plasma Membrane of NK cells. Their tie up leads to targeting the cells in action. This completes the cytotoxic immune response.
10. Which receptor is responsible for improving cytotoxicity of NK cells?
a) CD8
b) CD12
c) CD16
d) CD4
View Answer
Explanation: NK cells express various inhibitory as well as activating receptors in order to inhibit the growth and spread of infectious cells and help in differentiation and proliferation processes respectively. Improving the cytotoxicity of NK cells is very important to enhance the activity of these cells. CD16 is an important receptor due to which there is an improvement of cytotoxicity of these cells. For example, in case of tumour cells, CD16 binds to the Fc region of antibody and promotes antibody-dependent cell-mediated cytotoxicity of NK cells. Once the cytotoxicity of NK cells is enhanced, they get activated in order to target the tumour cells.
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