Immunology Second Line of Host Defense
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Questions and Answers

What role does fever play in the second line of host defense?

  • It promotes phagocytosis by white blood cells.
  • It directly destroys pathogens through cytotoxicity.
  • It enhances the production of antibodies by B cells.
  • It resets the hypothalamus thermostat to a higher setting. (correct)

    • Which cells are primarily responsible for producing histamine during the inflammatory response?

  • Macrophages
  • Neutrophils
  • Mast cells (correct)
  • Eosinophils

    • Which of the following is NOT a type of antimicrobial substance involved in the second line of defense?

  • Antibodies (correct)
  • Complement
  • Interferons
  • Lysozymes

    • What is phagocytosis primarily defined as?

    <p>The process of 'eating' and removing pathogens.</p> Signup and view all the answers

    Which leukocyte type predominates early in an infection?

    <p>Neutrophils</p> Signup and view all the answers

    What are the primary functions of eosinophils in the immune response?

    <p>Toxins against parasites.</p> Signup and view all the answers

    Which of the following cytokines is NOT considered pro-inflammatory?

    <p>Interferons</p> Signup and view all the answers

    What blood cell type is responsible for the majority of the phagocytic activity?

    <p>Neutrophils</p> Signup and view all the answers

    What is the primary function of neutrophils in the immune response?

    <p>Eating and killing bacteria</p> Signup and view all the answers

    Which of the following is NOT a stage of phagocytosis?

    <p>Inhibition</p> Signup and view all the answers

    What role do opsonins play in phagocytosis?

    <p>Help in the attachment of phagocytes to pathogens</p> Signup and view all the answers

    What chemical is specifically mentioned as a chemotactic substance for monocytes?

    <p>Monocyte chemotactic protein-1</p> Signup and view all the answers

    During which phase of phagocytosis does the phagocyte plasma membrane extend to engulf the pathogen?

    <p>Ingestion</p> Signup and view all the answers

    Which enzymes are involved in the digestion stage of phagocytosis?

    <p>Lysozymes and lipases</p> Signup and view all the answers

    What happens to the residual body after digestion in phagocytosis?

    <p>It undergoes exocytosis</p> Signup and view all the answers

    What is the role of macrophages in phagocytosis compared to neutrophils?

    <p>Macrophages are slower but more effective at killing pathogens.</p> Signup and view all the answers

    What is one of the primary functions of the complement system?

    <p>Lysis of foreign cells</p> Signup and view all the answers

    Which statement is true regarding the components of the complement system?

    <p>They remain inactive until cleaved.</p> Signup and view all the answers

    Which of the following is NOT a characteristic of Natural Killer (NK) cells?

    <p>They are a type of antigen-presenting cell.</p> Signup and view all the answers

    Which pathway of the complement system is the most specific?

    <p>Classical pathway</p> Signup and view all the answers

    What role do lysozymes play in the oxygen-independent killing mechanism?

    <p>They hydrolyze mucopeptides in the cell wall.</p> Signup and view all the answers

    What happens to the complement's lytic activity when heated to 56 ºC for 30 minutes?

    <p>It is destroyed.</p> Signup and view all the answers

    Which of the following effector molecules is responsible for depriving pathogens of iron?

    <p>Lactoferrin</p> Signup and view all the answers

    How are the fragments of complement components designated when cleaved?

    <p>By lowercase letters and numbers.</p> Signup and view all the answers

    What type of pathogens does Mannose-binding Lectin (MBL) primarily bind to?

    <p>Bacteria, yeasts, viruses, and parasites</p> Signup and view all the answers

    Which complement pathway is characterized by being antibody-dependent?

    <p>Classical pathway</p> Signup and view all the answers

    What is the primary role of C3b during complement activation?

    <p>Promotion of phagocytosis</p> Signup and view all the answers

    Which statement accurately describes the role of regulatory proteins in complement activation?

    <p>They limit damage to host cells</p> Signup and view all the answers

    What is the mechanism by which lysozyme acts on bacteria?

    <p>Disrupts the peptidoglycan layer of cell walls</p> Signup and view all the answers

    Which type of interferon is primarily produced by T cells and NK cells?

    <p>Type II interferon</p> Signup and view all the answers

    Which consequence of complement activation leads to the formation of a membrane attack complex (MAC)?

    <p>Cytolysis</p> Signup and view all the answers

    Which type of carbohydrate does mannose-binding lectin bind to on pathogens?

    <p>D-mannose and L-fucose</p> Signup and view all the answers

    What is the primary role of acute-phase proteins in the body?

    <p>To enhance the immune response</p> Signup and view all the answers

    Which of the following proteins is considered a positive acute-phase protein?

    <p>C-reactive protein</p> Signup and view all the answers

    How does the innate immune system differ from the adaptive immune system in terms of specificity?

    <p>Innate immunity is non-specific</p> Signup and view all the answers

    Which characteristic is NOT associated with the adaptive immune system?

    <p>Rapid response</p> Signup and view all the answers

    What type of cells are primarily involved in the adaptive immune response?

    <p>B and T cells</p> Signup and view all the answers

    What is the approximate time frame for the adaptive immune response to become fully effective?

    <p>Weeks</p> Signup and view all the answers

    Which feature is common to both the innate and adaptive immune systems?

    <p>Presence of physical and chemical barriers</p> Signup and view all the answers

    What is a major cytokine secreted by local inflammatory cells?

    <p>Tumor Necrosis Factor-alpha</p> Signup and view all the answers

    Study Notes

    Immunology (Second Line of Host Defense)

    • Second Line of Host Defense Components:
      • Fever
      • Inflammation
      • Phagocytosis
      • Natural killer cells
      • Antimicrobial Substances:
        • Complement
        • Interferons
        • Lysozymes
        • Acute phase proteins

    Fever

    • Definition: A systemic non-specific response to infection.
    • Pyrogen Sources:
      • Exogenous: LPS, pathogens, foreign cells, vaccines.
      • Endogenous: Interleukin-1 (IL-1 and 6) and Tumor necrosis factor (TNF-α).
    • Mechanism: Monocytes, neutrophils, and macrophages reset the hypothalamus (in the brain) thermostat to a higher setting.
    • Significance: Low-grade fever (38-38.5°C) is an effective defense against disease.

    Inflammation

    • Mechanism of Action: When pathogens cross skin/mucous membranes into the body, injury to tissues and histamine release initiates this response.
    • Key Players: Mast cells (primarily), and then basophils, are the major histamine producers.

    Pro-Inflammatory Cytokines

    • List: Tumor necrosis factor (TNF-α), Interleukin-1, Interleukin-6, Interleukin-8, Chemokines, Interferons.

    Phagocytosis

    • Definition: "Eat and cell," a process by white blood cells (monocytes/macrophages, neutrophils, and occasionally eosinophils and dendritic cells).
    • Neutrophils: Predominate early in infections.
    • Macrophages (Histiocytes): Fixed locations in tissues such as liver, nervous system, lungs, lymph nodes.
    • Phagotic Cells (details):
      • Macrophage: Monocytes that reside in tissues and organs. They can phagocytose, or secrete toxic substances for killing pathogens. They are also antigen-presenting cells (APCs).
      • Monocyte: Functions in blood similar to macrophages in tissues, transforming into macrophages. Phagocytosis in tissues and organs, also APCs.
      • Neutrophil: Phagocytosis and secretion of substances involved in inflammation.
      • Dendritic Cell: Phagocytosis in tissues and organs, while being antigen-presenting cells (APCs). They link innate and adaptive immune responses.

    Origin of Phagocytic Cells (Macrophages, Neutrophils, and Eosinophils)

    • Origin: Myeloid and Lymphoid stem cells.

    Cellular Elements of Blood

    • Cell Type | # Cells/mm³ | Function
    • Erythrocytes (RBC) | 4.8-5.4 million | Carry O2 and CO2
    • Leukocytes (WBC) | 5000-9000 | Various (including phagocytosis, antibody production)
    • Granulocytes | |
    • Neutrophils (Microphage) | 70% WBC | Phagocytosis
    • Basophils | 1% | Produce histamine
    • Eosinophils | 4% | Toxins against parasites, some phagocytosis
    • Agranulocytes | |
    • Monocytes (Macrophages) | 5% | Phagocytosis
    • Lymphocytes | 20% | Antibody production and cell-mediated immunity
    • Platelets | 300,000 | Blood clotting

    Stages of Phagocytosis

    • Chemotaxis: Phagocytes attracted to infection site by chemical factors from microbes, damaged tissues and inflammatory cells.
    • Adherence: Phagocyte plasma membrane adheres to pathogen/foreign material. Bacterial capsules can inhibit adherence. Opsonization (coating) with opsonins enhances adherence (antibodies and complement proteins).
    • Ingestion (Endocytosis): Phagocyte extensions (pseudopods) engulf the microbe, enclosing it in a phagosome.
    • Digestion: Phagosome fuses with a lysosome forming a phagolysosome. Lysosomal enzymes kill microbes (e.g., lysozymes, lipases, proteases, RNAses, DNAses) within minutes.
    • Exocytosis: Undigested material is discharged

    Natural Killer (NK) Cells

    • Description: Large granular lymphocytes (LGL).
    • Function: Kill virus-infected and tumor cells. They secrete cytokines such as IFNγ and TNFα.
    • Activation: Activated by IL-2 and IFN-γ to become Lymphokine Activated Killer (LAK) cells.

    5.a. Complement

    • Definition: A large group of serum proteins (around 30 types).
    • Functions: Lysis of foreign cells, inflammation, and phagocytosis.
    • Inactivation: Lytic activity is destroyed upon heating at 56°C for 30 minutes.
    • Origin: Produced mainly by hepatocytes, monocytes, and epithelial cells (GI & Genitourinary tracts)
    • Complement Components (Nomenclature):
      • Many are proenzymes (zymogens) until activated.
      • Named with capital letters (C1, C2...), with cleaved fragments having small letters (C3a, C3b).

    Complement Pathways

    • Classical Pathway: Antibody-dependent, most specific, using C1.
    • Lectin Pathway: Some specificity, using mannose-binding protein to bind C4.
    • Alternative Pathway: Non-specific, auto-activation of C3.

    Mannose-binding Lectin (MBL) Pathway

    • MBL Function: Binds to carbohydrates (D-mannose and L-fucose) on pathogen surfaces (e.g., bacteria, yeasts, viruses, parasites).

    Consequences of Complement Activation

    • Cytolysis: Formation of the Membrane Attack Complex (MAC) creates lesions in microbial membranes.
    • Inflammation: Complement components (C3a) trigger histamine release, increasing vascular permeability.
    • Opsonization: Complement components (C3b) bind microbial surfaces enhancing phagocytosis.
    • Inactivation of Complement: Regulatory proteins prevent damage to host cells.

    5.b. Interferons

    • Description: Antiviral proteins.
    • Functions: Interfere with viral replication, important in acute/short-term infections.
    • Specificity: Host-specific but not virus-specific.
    • Types:
      • Type I (α, β): Produced by lymphocytes and macrophages (α), fibroblasts and epithelial cells (β).
      • Type II (γ): Produced by T cells and NK cells.

    5.c. Lysozyme

    • Description: An antimicrobial enzyme in the innate immune system.
    • Function: A glycoside hydrolase that catalyzes the hydrolysis of 1,4-beta-linkages between N-acetylmuramic acid and N-acetyl-D-glucosamine residues in peptidoglycan, a major component of Gram-positive bacterial cell walls causing bacterial lysis.
    • Location: Abundant in secretions like tears, saliva, human milk, and mucus; also in macrophage and neutrophil cytoplasmic granules.

    5.d. Acute-Phase Proteins

    • Description: Proteins whose plasma levels change in response to inflammation.
    • Functions: Fever, acceleration of peripheral neutrophil circulation, and repair from tissue damage.
    • Mechanism: Local inflammatory cells (neutrophils and macrophages) release cytokines (IL-1, IL-6, IL-8, and TNF-α) into the bloodstream, stimulating the liver to produce various acute-phase proteins (ex: C-reactive protein).

    Innate Immunity vs. Adaptive Immunity

    • Innate: Present from birth. Non-specific; rapid response; limited/lower potency; no immunological memory; includes physical and chemical barriers, phagocytes, leukocytes, dendritic cells, and NK cells.
    • Adaptive: Developed in response to foreign exposure. Specific response to pathogens/antigens; slower response; high potency; immunological memory; involves B and T cells (cell-mediated and humoral).

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    Immunology Lecture Second Line of Host Defense 2023 PDF

    Description

    Test your knowledge on the second line of host defense in immunology, including the roles of fever, inflammation, and phagocytosis. This quiz covers various components such as natural killer cells and antimicrobial substances like complement and interferons. Dive into how these mechanisms work together to protect the body against infections.

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