Lecture 2.2 - The innate immune system
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Questions and Answers

What is the definition of an infectious disease?

  • When the normal flora is depleted by antibiotic therapy
  • When the host's immune system succeeds in eliminating the pathogen
  • When the host's immune system is compromised
  • When the pathogen succeeds in evading and/or overwhelming the host's immune defences (correct)

    • Which of the following is NOT a factor that can lead to clinical problems?

  • Overgrowth of normal flora due to immune-compromised host
  • Vaccination (correct)
  • Breaching of skin integrity
  • Displacement of normal flora from its normal location to a sterile location

    • What is the term for the cells and organs that contribute to immune defences against infectious and non-infectious conditions?

  • Normal flora
  • Pathogen
  • Innate barriers
  • Immune system (correct)

    • Which of the following is an example of a normal flora that can become pathogenic?

    <p>All of the above</p> Signup and view all the answers

    What happens when the normal flora is depleted by antibiotic therapy?

    <p>Both A and B</p> Signup and view all the answers

    Which of the following is a high-risk patient group that is more susceptible to serious infections?

    <p>All of the above</p> Signup and view all the answers

    What is the term for the initial response that occurs when the pathogen overcomes the innate barriers and enters the body?

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

    Which of the following is an example of breaching the skin integrity?

    <p>All of the above</p> Signup and view all the answers

    Which of the following complement proteins is NOT initiated by antibody-antigen?

    <p>C3</p> Signup and view all the answers

    What is the primary function of opsonins such as C3 and C4?

    <p>To mark pathogens for phagocytosis and clearance</p> Signup and view all the answers

    Which of the following is NOT an example of an acute phase protein?

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

    What is the primary mechanism by which the complement system contributes to the clearance of pathogens?

    <p>complement proteins form a membrane attack complex, leading to lysis of the pathogen</p> Signup and view all the answers

    Which of the following pathways is initiated by cell surface microbial constituents, such as endotoxins on E. coli?

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

    What is the primary function of Fc receptors on phagocytes such as macrophages and neutrophils?

    <p>To bind to the Fc region of an antibody-opsonized pathogen</p> Signup and view all the answers

    What is the primary function of pattern recognition receptors (PRRs) on macrophages?

    <p>To recognize and phagocytose pathogen-associated molecular patterns (PAMPs)</p> Signup and view all the answers

    Which of the following cytokines is responsible for neutrophil recruitment in blood vessels?

    <p>IL-8</p> Signup and view all the answers

    What is the result of mast cell degranulation during inflammation?

    <p>Release of histamine and increased allergic response</p> Signup and view all the answers

    Which of the following is NOT a local inflammatory action of cytokines?

    <p>Systemic increase in body temperature</p> Signup and view all the answers

    What is the role of C-reactive protein (CRP) in the immune response?

    <p>It acts as an opsonin to enhance phagocytosis</p> Signup and view all the answers

    Which of the following cells is responsible for presenting antigens to T and B cells, initiating the specific adaptive immune response?

    <p>Dendritic cells</p> Signup and view all the answers

    What is the result of cytokine-mediated inflammation in blood vessels?

    <p>Vasodilation and increased blood flow</p> Signup and view all the answers

    Which of the following pathways is activated by the presence of pathogens in the immune response?

    <p>Either the lectin or alternative pathway</p> Signup and view all the answers

    What is the primary mechanism by which macrophages destroy pathogens?

    <p>Production of reactive oxygen species</p> Signup and view all the answers

    What is the result of decreased phagocytosis in asplenic patients?

    <p>Reduced ability to combat pathogenic insults</p> Signup and view all the answers

    Which of the following is an example of an oxygen-independent pathway?

    <p>Production of lysozyme</p> Signup and view all the answers

    What is the primary function of NETs?

    <p>To trap pathogens extracellularly</p> Signup and view all the answers

    What is the result of decreased neutrophil number?

    <p>Reduced ability to combat pathogenic insults</p> Signup and view all the answers

    What is the process by which neutrophils externally trap pathogens?

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

    Study Notes

    Immune System and Infectious Disease

    • The immune system consists of cells and organs that contribute to immune defenses against infectious and non-infectious conditions, distinguishing between self and non-self.
    • Infectious disease occurs when a pathogen succeeds in evading and/or overwhelming the host's immune defenses.

    Innate Barriers

    • Innate barriers include microbiota (commensals) that live on the skin and in the nasopharynx, such as Staphylococcus aureus, Streptococcus pneumoniae, and Candida albicans.
    • These microorganisms can become pathogenic under certain conditions.

    Clinical Problems

    • Clinical problems arise when:
      • Normal flora is displaced from its normal location to a sterile location.
      • The skin integrity is breached, e.g., through skin loss, IV lines, surgery, skin diseases, or injection drug use.
      • The fecal-oral route or fecal-perineal-urethral route is compromised, leading to infections such as foodborne infections or urinary tract infections.
      • There is poor dental hygiene or dental work, resulting in infections such as dental extraction or gingivitis.
      • Patients are at high risk, e.g., asplenic or hyposplenic patients, or those with damaged or prosthetic valves.

    The Immune Response

    • The initial immune response occurs when a pathogen overcomes the innate barriers and enters the body.
    • Macrophages recognize pathogen-associated molecular patterns (PAMPs) and phagocytose them, releasing cytokines that recruit other cells to the site of infection.
    • Cytokines also cause inflammation, leading to vasodilation, vascular permeability, mast cell degranulation, and clotting system activation.

    Microbes and PAMPs

    • Microbes have PAMPs that interact with pattern recognition receptors (PRRs) on innate cells.
    • This interaction leads to the activation of macrophages, monocytes, and neutrophils, which release cytokines such as TNF alpha, IL-1, IL-6, and IL-8.

    Phagocytosis and Opsonins

    • Phagocytosis is the process by which phagocytes (e.g., macrophages and neutrophils) internalize and destroy pathogens.
    • Opsonins, such as complement proteins, antibodies, and acute phase proteins, enhance phagocytosis by marking pathogens for destruction.
    • Examples of opsonins include C3, C4, IgG, IgM, CRP, and MBL.

    Clearance of Opsonized Pathogen

    • Complement proteins can "punch holes" in the pathogen's cell membrane, leading to death.
    • Phagocytes recognize opsonized pathogens through Fc receptors, internalize them, and produce reactive oxygen species to destroy the pathogen.

    Phagocyte Intracellular Killing Mechanisms

    • Oxygen-dependent pathway: respiratory burst produces toxic oxygen products (e.g., hydrogen peroxide, hydroxyl radical) that kill pathogens.
    • Oxygen-independent pathways: lysozyme, lactoferrin or transferrin, cationic proteins, proteolytic and hydrolytic enzymes, and NETs (neutrophil extracellular traps).

    NETosis

    • NETosis is the process by which neutrophils externally trap pathogens using decondensed chromatin and granule contents.
    • This mechanism can be used as a means of neutrophil cell death and is commonly used to deal with pathogenic insults.

    Summary of the Innate Immune Response

    • The innate immune response is a crucial defense against pathogens, involving the recognition of PAMPs, activation of macrophages and neutrophils, and the production of cytokines and opsonins.
    • Phagocytosis and intracellular killing mechanisms are essential for eliminating pathogens.

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    Related Documents

    Lecture 2.2 - The Innate Immune System PDF

    Description

    Understand the key factors that determine the outcome of a host-pathogen relationship, including the immune system's role in defending against infectious and non-infectious conditions. Learn about the innate barriers and microbiota's role in the immune response.

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