Question 1

NKT cells require antigen presentation by:
I- CD1
II- MHC class I molecules
III- MHC class II molecules

A) I only
B) III only
C) I and II
D) II and III
E) I, II, and III

I only

Accepted Answer

NKT cells require antigen presentation by CD1 molecules, while NK cells do not require antigen presentation at all. NKT cells do not recognize antigen presented on MHC class I or II molecules.

Question 2

NK cells produce which cytokine that activates macrophages?&#10;A) IL-1&#10;B) IL-13&#10;C) TNF-a&#10;D) Interferon-g

Accepted Answer

NK cells produce interferon-g, which activates macrophages. This increased macrophage response is important in the killing of extracellular pathogens.

Question 3

Individuals with Chediak-Higashi syndrome have a genetic defect that causes:&#10;A) The increased production of IL-13&#10;B) Increased numbers of NKT type I cells&#10;C) The inability to kill through the perforin and granzymes pathway&#10;D) The inability to produce activating and inhibiting receptors in the NK cell surface

Accepted Answer

Individuals with Chediak-Higashi syndrome have a defect in the Lyst gene, which causes the patient to have a variety of symptoms that are related to defective granules, including hypopigmentation and dysfunction of platelets and NK cells.

Question 4

Which of the following cell types may play a role in allergic reactions, particularly in relation to asthma?&#10;A) NK CD56dim cells&#10;B) NK CD56bright cells&#10;C) NKT type I cells&#10;D) NKT type II cells

Accepted Answer

Patients with severe asthma have been shown to have elevated numbers of NKT type I cells in bronchial and alveolar fluids. The cytokines produced by these cells may direct the production of IgE and may play a role in airway hyperresponsiveness, airway remodeling, mucus secretion, and recruitment of eosinophils.

Question 5

A host cell that has been infected with the influenza virus and has subsequently downregulated MHC class I molecules is most likely to be recognized by which cell type?&#10;A) T cell&#10;B) B cell&#10;C) NK cell&#10;D) Neutrophil

Accepted Answer

NK cells recognize host cells that have downregulated MHC class I molecules, and proceed to destroy the cell in order to destroy the viral reservoir. Cytotoxic T cells will recognize infected host cells that present antigen on MHC class I molecules and will destroy those cells. B cells and neutrophils are more likely to recognize extracellular antigens, rather than cells that are infected with intracellular antigens.

Question 6

Which is the main surface molecule on NK cells that is involved in antibody-dependent cell-mediated cytotoxicity (ADCC)?&#10;A) CD3&#10;B) CD16&#10;C) CD56&#10;D) CD94

Accepted Answer

CD16 is the surface receptor that recognizes the Fc portion of antibodies bound to the target cells, initiating ADCC.

Question 7

NK cells have cell surface receptors that contain immunoreceptor tyrosine-based inhibitory motifs (ITIMs), which bind ligand and recruit which type of molecule to transmit the inhibitory signal?&#10;A) cAMP&#10;B) Kinase&#10;C) ATPase&#10;D) Phosphatase

Accepted Answer

The inhibitory molecules recruit phosphatases, which dephosphorylate receptors, leading to transmission of the inhibitory signal.

Question 8

Which cell type can kill target cells using the perforin and granzymes method?&#10;A) NKT type I cells&#10;B) NKT type II cells&#10;C) NK CD56dim cells&#10;D) NK CD56bright cells

Accepted Answer

The CD56ᵈᶦᵐ NK cells, along with CTLs, contain low numbers of the CD56 marker and possess perforin and granzymes in their granules, which cause apoptotic cell death in target cells. The other cell types listed do not contain perforin and granzymes and have other functions in the immune response. While NKT type II cells have not been studied extensively, NK CD56ᵇʳᶦᵍʰᵗ cells and NKT type I cells have proinflammatory functions.

Question 9

Which of the following is true concerning natural killer (NK) cells?&#10;A) NK cells never express CD16.&#10;B) NK cells never express CD56.&#10;C) NK cells express both B and T cell markers.&#10;D) NK cells do not express B or T cell markers.

Accepted Answer

NK cells do express CD56, and many express CD16, which is a receptor that recognizes Fc portions of antibodies. NK cells do not express B or T cell markers, while NKT cells do express the T cell marker CD3.

Question 10

If a host cell expresses both MHC class I molecules and ligands that bind activating receptors on NK cells, what is the outcome for the host cell?&#10;A) The host cell will not be killed because the NK cell needs two different activating signals to kill a host cell.&#10;B) The host cell will not be killed because the MHC class I molecules cause inhibition that overrides the activating signals.&#10;C) The host cell will be killed because the NK cell does not bind MHC class I molecules and the activating signal causes cell death.&#10;D) The host cell will be killed because the activating signal overrides the inhibitory signal caused by the MHC class I molecule binding.

Accepted Answer

The NK cell will recognize and bind to activating ligands and to MHC class I molecules on an infected host cell. However, the presence of MHC class I molecules serves an inhibitory function over the activating signals. The activating receptors are phosphorylated, and the inhibitory receptors recruit phosphatases to dephosphorylate the activating receptors, thus inactivating the activating receptors. This serves as a protective mechanism so that host cells are not inappropriately killed by NK cells. NK cells kill the infected host cell only when the MHC class I molecules are downregulated. Infected cells that present antigen on MHC class I molecules can be killed by cytotoxic T cells (CTLs).

Deck 21: Natural Killer Cells