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Questions and Answers
What is a key function of type-1 interferons in host defense against viral infections?
Which type of immune cell is NOT part of the innate immune system?
What is the primary role of the complement system in innate immunity?
What does TNF-α release by macrophages primarily cause?
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Which of these is NOT a characteristic of pattern recognition receptors (PRRs)?
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Which cellular event is directly triggered by the recognition of viral particles within an infected cell?
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What is one of the functions of microbiota in the context of the innate immune system?
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Neutrophil recruitment during inflammation is primarily influenced by which type of signaling?
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What role do Type-1 interferons play in the immune response?
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Which receptors are associated with NK cell activation?
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What is the main function of perforins in the immune response?
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Where do lymphocytes mature in the body?
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What structure in the immune system connects innate and adaptive immunity?
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What activates adaptive immune responses in peripheral lymphoid tissues?
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What is the role of lymph nodes in the immune response?
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Which statement best describes secondary lymphoid tissue?
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Study Notes
Recap of Innate Immunity
- Physical barriers include epithelial linings, mucosal linings, mucus, and tears.
- Chemical barriers include acidic pH, enzymes, AMPs, and complement.
- Microbiological barriers include microbiota.
- Innate immune cells include macrophages, neutrophils, and NK cells.
Complement Cascade in Innate Immunity
- Complement cascade is a system of proteins that is activated by pathogens.
- Once activated, it forms a complex that can lyse pathogens, recruit inflammatory cells, and opsonize pathogens for phagocytosis.
Outcomes of Complement Activation
- Three outcomes of complement activation:
- Direct pathogen lysis
- Recruitment of inflammatory cells
- Opsonization for phagocytosis
Complement System in Opsonization and Phagocytosis
- Complement proteins bind to the pathogen surface.
- These proteins are recognized by receptors on phagocytic cells.
- Phagocytes engulf the pathogen.
Cellular Locations of PRRs
- PRRs are located in different subcellular compartments.
- This allows different innate immune cells to sense danger in various places and respond effectively to diverse pathogens.
Detection of PAMPs by TLRs
- Toll-like receptors (TLRs) are a family of PRRs that are expressed by different immune cells.
- Each TLR recognizes a different type of PAMP.
- Once a TLR binds to its PAMP, it activates signaling pathways that lead to the production of inflammatory cytokines.
TLR Signaling Pathways
- TLRs activate signaling pathways that lead to the production of inflammatory cytokines.
- The precise response depends on the type of TLR and the host cell involved.
Inflammation and Neutrophil Recruitment
- Inflammatory cytokines, such as TNF-alpha, IL-1, and IL-6, attract neutrophils to the site of infection.
- This attracts other immune cells to the site and help to contain the infection.
Neutrophil Recruitment
- Neutrophils infiltrate the site of infection and phagocytose pathogens.
- They release antimicrobial substances.
TNF-α and Systemic Release
- TNF-alpha can be damaging when released systemically, which can lead to a cytokine storm.
- This is dangerous, leading to tissue damage and organ failure.
Interferons in Viral Infection
- Interferons (IFNs) are a type of cytokine that helps to protect against viral infection.
- Type-1 interferons inhibit viral replication and activate innate immune cells such as NK cells.
Inhibitory and Activating Receptors of NK Cells
- NK cells are involved in eliminating virus-infected cells and cancer cells.
- They have inhibitory receptors that prevent them from attacking healthy cells.
- They also express activating receptors that trigger cell death.
Dendritic Cells Link Innate and Adaptive Immunity
- DCs are a type of antigen-presenting cell.
- DCs bridge innate and adaptive immunity by engulfing pathogens and presenting antigens to T lymphocytes.
Innate vs. Adaptive Immunity
- Innate immunity is the first line of defense against infection.
- Adaptive immunity is a more specialized response that is tailored to a particular pathogen.
Lymphocytes in Adaptive Immunity
- Lymphocytes are specialized cells of the adaptive immune system.
- These include B cells and T cells.
Principles of Clonal Selection
- Clonal selection is a fundamental principle of adaptive immunity.
- Each lymphocyte expresses a unique receptor specific for one antigen, and when stimulated by that antigen, it will proliferate and differentiate into a clone of effector cells.
Lymphocyte Maturation and Location
- Lymphocytes mature in the bone marrow (B cells) or the thymus (T cells).
- Then, they congregate in lymphoid tissues throughout the body.
Distribution of Lymphoid Tissues
- Central (primary) lymphoid tissues include the bone marrow and the thymus.
- Peripheral (secondary) lymphoid tissues include lymph nodes, spleen, and mucosal-associated lymphoid tissues (MALT).
Antigen-Presenting Cells in Adaptive Immune Responses
- Antigen-presenting cells (APCs) play a crucial role in initiating adaptive immune responses.
- They present antigens to T lymphocytes, which then trigger the adaptive immune response.
Antigen Encounter in Peripheral Lymphoid Tissues
- Circulating lymphocytes encounter antigens in peripheral lymphoid tissues.
- This is where adaptive immune responses are initiated.
Organization of a Lymph Node
- Lymph nodes are strategically located along lymphatic vessels.
- They provide a site for lymphocytes to interact with APCs.
Peyer’s Patches in Mucosa
- MALTs are specialized immune structures that are located in mucosal tissues.
- Peyer's Patches are localized in the gut mucosa and are designed to sample antigens from the gut lumen.
Checkpoint Questions
- Primary Lymphoid Tissues: Bone marrow and thymus where lymphocytes mature.
- Secondary Lymphoid Tissues: Lymph nodes, spleen, and MALT, where lymphocytes encounter antigens and initiate adaptive immune responses.
- T Cell Activation: T cells are activated in the paracortex of lymph nodes.
- B Cell Activation: B cells are activated in the germinal centers of lymph nodes.
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Description
Test your understanding of innate immunity concepts, including physical, chemical, and microbiological barriers, as well as the complement cascade. This quiz also covers the roles of innate immune cells and the mechanisms of opsonization and phagocytosis. Dive into the details of how your body defends itself against pathogens!
