Ch2pp37-43

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Questions and Answers

What is the approximate percentage of NK cells in the blood and secondary lymphoid organs?

1% to 5%

10% to 15%

5% to 20% (correct)

20% to 25%

Which of the following is true about NK cells' antigen receptors?

They do not express immunoglobulins or TCRs (correct)

They express immunoglobulins but not TCRs

They express immunoglobulins and TCRs

They express TCRs but not immunoglobulins

What activates macrophages to kill phagocytosed microbes?

IFN-γ

IL-12 (correct)

IFN-α

IL-6

What is the function of NK cells in response to infected cells?

Induce apoptosis in infected cells Signup and view all the answers

Which of the following is a function of cytokines in innate immunity?

Recruiting blood neutrophils and monocytes Signup and view all the answers

Which complement activation product leads to opsonization and phagocytosis through its deposition on microbes?

$C3b$ Signup and view all the answers

Which cytokine is induced by bacterial PAMPs and can lead to septic shock characterized by low blood pressure and disseminated intravascular coagulation?

$TNF$ Signup and view all the answers

Which type of IFNs, produced in viral infections, inhibit viral replication and prevent spread of the infection to uninfected cells?

Type I IFNs Signup and view all the answers

What is the function of C5b in complement activation?

$Formation$ of membrane attack complex (MAC) causing lysis of the microbe Signup and view all the answers

Which cells secrete cytokines in innate immunity in response to microbes or other cytokines?

$Dendritic$ cells Signup and view all the answers

What are the effector functions of products from alternative, classical, and lectin pathways of complement activation?

Both inducing inflammation and opsonization/phagocytosis Signup and view all the answers

Which cytokine activates NK cells and macrophages?

IL-12 Signup and view all the answers

What is the main function of C3a released during complement activation?

Inducing inflammation Signup and view all the answers

Which cells produce type I IFNs in viral infections?

Dendritic cells Signup and view all the answers

What is the potent stimuli for cytokine secretion in innate immunity?

Microbial nucleic acids Signup and view all the answers

Which complement pathway is triggered by antibodies binding to microbes?

Classical pathway Signup and view all the answers

Which plasma protein recognizes microbial carbohydrates and activates the complement cascade?

Plasma MBL Signup and view all the answers

What is the central component of all three complement pathways?

C3 Signup and view all the answers

Which immune cells compensate for defective CTL response in the host-microbe struggle?

NK cells Signup and view all the answers

What are the main functions of the complement system in host defense?

Opsonization and phagocytosis, inflammation, and cell lysis Signup and view all the answers

Which pathway is a component of innate immunity, triggered when complement proteins are activated on microbial surfaces without control due to the absence of complement regulatory proteins on microbes?

Alternative pathway Signup and view all the answers

Which cytokines are known to activate NK cells?

IL-15, type I IFNs, and IL-12 Signup and view all the answers

What is the function of inhibitory receptors on NK cells?

Block signaling by activating receptors and are specific for self class I major histocompatibility complex (MHC) molecules Signup and view all the answers

What is the principal function of NK cells in antibody-dependent cellular cytotoxicity (ADCC)?

Mediating the killing of antibody-coated target cells Signup and view all the answers

What determines NK cell responses?

A balance between engaging activating and inhibitory receptors Signup and view all the answers

How do activated macrophages contribute to NK cell function?

Release IL-12, which produces IFN-gamma from NK cells, leading to the killing of phagocytosed microbes Signup and view all the answers

What is the role of activating receptors on NK cells?

Enable NK cells to eliminate cells infected with intracellular microbes, irreparably injured cells, and tumor cells Signup and view all the answers

How do many viruses evade killing by NK cells?

They downregulate ligands for activating receptors Signup and view all the answers

Study Notes

Natural Killer (NK) Cell Activation and Function

NK cells bind to virus-infected cells and kill them
Activated macrophages release IL-12, which produces IFN-gamma from NK cells, leading to the killing of phagocytosed microbes
Cytokines secreted by macrophages and dendritic cells enhance NK cells' ability to protect against infections
IL-15, type I IFNs, and IL-12 are NK cell-activating cytokines
NK cells and macrophages function cooperatively to eliminate intracellular microbes
NK cell responses are determined by a balance between engaging activating and inhibitory receptors
Activating receptors enable NK cells to eliminate cells infected with intracellular microbes, irreparably injured cells, and tumor cells
NK cells are the principal mediators of antibody-dependent cellular cytotoxicity (ADCC)
Activating receptors on NK cells have signaling subunits containing immunoreceptor tyrosine-based activation motifs (ITAMs)
Inhibitory receptors of NK cells block signaling by activating receptors and are specific for self class I major histocompatibility complex (MHC) molecules
Many viruses have developed mechanisms to block expression of class I molecules in infected cells to evade killing by NK cells
The text includes a figure depicting the engagement of inhibitory and activating receptors of NK cells with healthy and infected cells.

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Description

Test your knowledge about complement activation and the peptide by-products C3a and C5a. Explore the functions and regulation of the complement system as well as the effector functions of products obtained from different pathways.