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Questions and Answers
What is NOT a component of innate immunity?
Which of the following is a primary physical barrier in innate immunity?
Which cytokine is produced by macrophages to stimulate immune responses?
What is the function of the complement system in innate immunity?
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Which cells produce Type I interferons (IFN-α and IFN-β)?
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What type of receptors recognize pathogen-associated molecular patterns (PAMPs)?
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How do natural killer (NK) cells assist in immunity?
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What role does normal flora play in immunity?
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What are toxic oxygen species produced by phagocytes during microbial killing?
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Which factor does NOT contribute to creating a protective environment on skin and mucosal surfaces?
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What is the mechanism by which complement enhances bacterial clearance?
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What role does Factor D play in the alternative complement pathway?
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How does the C1 inhibitor regulate complement activity?
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What is hereditary angioedema (HAE) caused by?
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Which statement differentiates the lectin pathway from the classical pathway?
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What is the function of mannose-binding lectin (MBL) in complement activation?
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Which infections are commonly associated with complement deficiencies?
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How can bacteria evade the innate immune system?
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What is the role of complement in linking innate and adaptive immunity?
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What distinguishes innate immunity from adaptive immunity?
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What is the primary function of C-reactive protein (CRP) in immunity?
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How do defensins contribute to the immune response?
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What initiates acute inflammation?
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What is the primary role of leukocyte extravasation during inflammation?
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Which complement activation pathway does not require antibodies?
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What are the key activators of the alternative complement pathway?
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What is the primary function of C3b in the complement system?
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Which of the following statements about the membrane attack complex (MAC) is true?
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What roles do C3a and C5a play in the complement activation process?
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Study Notes
Innate Immunity: Key Components & Mechanisms
- Innate immunity is the body’s first line of defense against pathogens. It is non-specific and acts rapidly.
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Components:
- Physical barriers: Skin, stomach acidity, mucus, cilia, microflora, lysozyme in tears, and flushing of the urinary tract.
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Cellular components:
- Phagocytes: Neutrophils, monocytes, and macrophages engulf and destroy pathogens.
- Natural killer (NK) cells: Kill host cells infected by intracellular microbes.
- Complement system: A group of proteins that aid in inflammation control, phagocytosis, and lysis of bacteria and virus-infected cells.
- Cytokines: Small soluble proteins produced by cells like macrophages, mediating immune and inflammatory reactions.
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Two important cytokines produced by macrophages are:
- Tumor necrosis factor (TNF)
- Interleukin-1 (IL-1)
- Toll-like receptors (TLRs): Pattern recognition receptors that recognize components of bacterial cells and activate macrophages.
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Activated macrophages perform the following:
- Phagocytosis of microbes: Engulfing and destroying pathogens.
- Production of reactive nitrogen species: Toxic molecules that kill microbes.
- Secretion of cytokines: Signaling molecules that mediate immune responses.
- Presenting antigens to T-cells: A key step in initiating adaptive immunity.
The Complement System: A Critical Player in Immune Defense
- Complement system is a cascade of proteins that work together to combat pathogens.
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Three pathways of activation:
- Classical pathway: Activated by antigen-antibody complexes involving IgG or IgM.
- Alternative pathway: Activated by bacterial cell walls, lipopolysaccharides (LPS), and cobra venom.
- Lectin pathway: Activated by mannose-binding lectin binding to microbial surfaces.
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Key Complement Functions:
- Opsonization (C3b): C3b binds to microbes, enhancing phagocytosis by immune cells.
- Inflammation promotion (C3a and C5a): These anaphylatoxins attract immune cells and promote inflammation.
- Cell lysis: Formation of the Membrane Attack Complex (MAC) creates pores in the membrane of pathogens, leading to cell lysis.
- C3 plays a central role in complement activation, contributing to opsonization, immune complex clearance, and MAC formation.
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Complement deficiencies can lead to increased susceptibility to infections, particularly those caused by:
- Haemophilus influenzae (alternative pathway defects)
- Neisseria infections (C5 deficiency)
Linking Innate and Adaptive Immunity
- Complement activation plays a vital role in linking innate and adaptive immunity.
- Complement components can enhance antigen presentation, promoting the activation of adaptive immune responses.
- The complement system provides a bridge between the rapid, non-specific innate immune response and the highly specific, adaptive immune response.
Additional Notes
- Defensins: Cationic proteins with antimicrobial activity, found in neutrophil granules and some macrophages. They protect epithelial surfaces by killing bacteria, fungi, and viruses.
- Acute inflammation: An immediate response to infection or tissue damage, characterized by redness, swelling, heat, and pain. Initiated by cytokine release from macrophages, dendritic cells, and mast cells.
- Leukocyte extravasation: Movement of white blood cells from the bloodstream to the site of infection.
- Normal flora: Microorganisms that normally reside on the body's surfaces and compete with pathogens.
- Pathogen-associated molecular patterns (PAMPs): Molecular structures present on pathogens but absent in host cells, recognized by pattern recognition receptors (PRRs).
- C-reactive protein (CRP): A protein made in the liver that binds phosphocholine on microbes and activates the classical complement pathway. It also neutralizes pro-inflammatory platelet-activating factor (PAF) and enhances phagocytosis of microbes.
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Description
Explore the fundamental aspects of innate immunity, your body's first line of defense against pathogens. This quiz covers key components such as physical barriers, cellular elements like phagocytes and NK cells, and the role of cytokines in immune responses. Test your knowledge on the mechanisms that govern our innate immune system.
