33 Questions
Which cells secrete type I IFNs in response to recognition of viral nucleic acids by TLRs, RLRs, and other pattern recognition receptors?
Plasmacytoid dendritic cells
What is the basis for the use of IFN-α to treat some forms of chronic viral hepatitis?
Inhibition of viral replication and destruction of viral genomes
What is associated with severe cases of COVID-19?
Inherited or acquired deficiency of type I IFN production or signaling
What enhances the ability of NK cells to kill infected cells?
Type I IFNs
Which cells secrete cytokines that induce inflammation?
Innate lymphoid cells (ILCs)
What activates macrophages to kill phagocytosed microbes?
Cytokine interferon-γ (IFN- γ)
What do complement proteins do when activated in innate immunity?
Coat (opsonize) microbes for phagocytosis, stimulate inflammation, and lyse microbes
What is the function of type I interferons in antiviral defense?
Inhibit viral replication
What do phagocytes do in inflammation?
Recruited from the circulation to sites of infection and tissue damage, ingest and destroy microbes and damaged cells
What ensures that adaptive immunity is elicited by microbes and not by nonmicrobial substances?
Requirement for second signals that work together with antigens to activate B and T lymphocytes
What is the role of natural killer (NK) cells in antiviral defense?
Kill host cells infected by intracellular microbes and produce the cytokine interferon-γ (IFN- γ)
What is the role of cytokines in innate immunity?
Stimulate inflammation, activate NK cells, activate macrophages, and prevent viral infections
What is the name of the first signal required for full activation of antigen-specific lymphocytes?
Signal 1
Why does the requirement for microbe-dependent second signals exist?
To ensure lymphocytes respond to infectious pathogens and not harmless substances
What may induce adaptive immune responses without microbes?
Adjuvants that elicit innate immune reactions
What are the second signals for T cells called?
Costimulators
How do blood-borne microbes activate the complement system?
Through the alternative pathway
What is the role of second signals in relation to adaptive immunity?
They stimulate adaptive immunity and guide the nature of the adaptive immune response
What constitutes innate immunity in multicellular organisms?
Intrinsic mechanisms of defense against infections
What are Toll-like receptors (TLRs) a major class of?
Innate immune system receptors that recognize different microbial products.
What do inflammasomes generate?
The active form of the proinflammatory cytokine interleukin-1β (IL-1β)
Which components are principal components of innate immunity?
Epithelial barrier cells, phagocytes, dendritic cells, mast cells, natural killer cells, cytokines, and plasma proteins.
What do epithelia provide as a defense against microbes?
Physical barriers against microbes, produce antimicrobial peptides, and contain lymphocytes.
Which mechanism prevents excessive tissue damage in innate immune responses?
Production of anti-inflammatory cytokines like IL-10 and IL-1 receptor antagonist
What is the role of type I interferons (IFN-α, IFN-β) in response to viral infections?
Interfering with viral replication and increasing susceptibility to CTL-mediated killing
What do pathogens do to evade innate immunity?
Resistance to phagocytosis, reactive oxygen intermediates, complement activation, and antimicrobial peptides
What is the function of innate immune responses besides combating infections?
Serving as a warning function, alerting the adaptive immune system of the need for an effective immune response
How is inflammasome activation controlled?
Tightly controlled by posttranslational modifications and micro-RNAs
How do intracellular bacteria like Listeria monocytogenes evade innate immunity?
Produce proteins enabling escape from phagocytic vesicles
What is the role of feedback mechanisms in innate immune responses?
Induce expression of inhibitors of cytokine signaling in response to TLR signaling
What do some intracellular bacteria like mycobacteria contain that inhibits fusion of phagosomes with lysosomes?
Lipids inhibiting fusion of phagosomes with lysosomes
What is the effect of microbial evasion on innate immunity?
Microbes have evolved mechanisms to evade innate immunity including resistance to various components like phagocytosis and antimicrobial peptides.
What do feedback mechanisms induce in response to TLR signaling?
Expression of inhibitors of cytokine signaling such as suppressors
Study Notes
Innate Immune Responses and Microbial Evasion
- Viral DNA recognition by CDSs induces autophagy, leading to the destruction of viral-containing organelles by lysosomes.
- Innate response to viral infections involves increased apoptosis of infected cells, aiding in the elimination of infection reservoirs.
- Innate immune responses are regulated by mechanisms preventing excessive tissue damage, including the production of anti-inflammatory cytokines like IL-10 and IL-1 receptor antagonist.
- Feedback mechanisms induce expression of inhibitors of cytokine signaling, such as suppressors of cytokine signaling (SOCS) in response to TLR signaling.
- Inflammasome activation is tightly controlled by posttranslational modifications and micro-RNAs.
- Type I interferons (IFN-α, IFN-β) are produced in response to TLR signaling and other viral nucleic acid sensors, interfering with viral replication and increasing susceptibility to CTL-mediated killing.
- Microbes have evolved mechanisms to evade innate immunity, including resistance to phagocytosis, reactive oxygen intermediates, complement activation, and antimicrobial peptides.
- Pathogenic microbes have evolved to resist innate immunity, with some intracellular bacteria and viruses encoding proteins that block induction of type I IFNs.
- Some intracellular bacteria, like Listeria monocytogenes, produce proteins enabling escape from phagocytic vesicles, while mycobacteria contain lipids inhibiting fusion of phagosomes with lysosomes.
- Innate immune responses not only combat infections but also serve as a warning function, alerting the adaptive immune system of the need for an effective immune response.
- Innate immune responses generate molecules that provide signals, in addition to antigens, required to activate naive T and B lymphocytes.
- The innate immune response to microbes stimulates adaptive immune responses, contributing to a comprehensive immune defense against infections.
Test your knowledge of the two signals required for full activation of antigen-specific lymphocytes and the concept of danger signals in the adaptive immune system.
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