Epithelial Surfaces and Antimicrobial Defense
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Epithelial Surfaces and Antimicrobial Defense

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Questions and Answers

What role do tight junctions between epithelial cells serve in the immune defense?

  • They allow extensive permeability for nutrient absorption.
  • They facilitate the production of antimicrobial proteins.
  • They promote the attachment of pathogens to epithelial surfaces.
  • They prevent the entry of pathogens by maintaining a barrier. (correct)
  • Which of the following are antimicrobial peptides mentioned in the immune defense?

  • Defensins and cathelicidins (correct)
  • Carbohydrate-binding proteins
  • Bile salts and fatty acids
  • Histones and lysozymes
  • What is the primary function of lysozyme in the immune response?

  • To neutralize toxins produced by pathogens.
  • To break down peptidoglycan in bacterial cell walls. (correct)
  • To inhibit the growth of viruses directly.
  • To act as a carbohydrate-binding protein.
  • Which aspect of mucosal epithelia contributes to preventing bacterial attachment?

    <p>The coating of bacteria with mucins.</p> Signup and view all the answers

    How do C-type lectins contribute to the immune defense?

    <p>By binding to carbohydrate structures on pathogens.</p> Signup and view all the answers

    What is one consequence of environmental stressors like drought on epithelial barriers?

    <p>They can disrupt the integrity of barriers, allowing pathogen invasion.</p> Signup and view all the answers

    What are the primary mechanisms by which epithelial cells deter pathogen invasion?

    <p>Production of antimicrobial proteins and mechanical movements.</p> Signup and view all the answers

    What is the significance of commensal bacteria in the context of epithelial barriers?

    <p>They outcompete harmful bacteria for resources.</p> Signup and view all the answers

    What is a primary function of antibodies in relation to pathogens?

    <p>To bind pathogens and block their access to cells</p> Signup and view all the answers

    Which effector mechanism specifically facilitates phagocytosis?

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

    What distinguishes the two main classes of T cells?

    <p>The presence of specific co-receptors on their surface</p> Signup and view all the answers

    How does the complement system primarily function in immune defense?

    <p>By activating and regulating other immune responses</p> Signup and view all the answers

    Where do T-cells develop in the human body?

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

    What mechanism is used by antibodies to prevent viruses from entering host cells?

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

    What are the specific receptors called that T-cells use to recognize peptide:MHC complexes?

    <p>T-cell receptors</p> Signup and view all the answers

    Which type of immunity is primarily mediated by antibodies?

    <p>Humoral immunity</p> Signup and view all the answers

    Which pathway of complement activation is triggered specifically by the presence of antibodies?

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

    What is the initial step in the activation of complement proteins?

    <p>Proteolytic cleavage</p> Signup and view all the answers

    What is the primary function of membrane attack in the complement system?

    <p>Directly destroy pathogens</p> Signup and view all the answers

    How are most proteins of the complement system produced?

    <p>By the liver</p> Signup and view all the answers

    Which mechanism of the complement system does NOT require the presence of antibodies for activation?

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

    What process is involved in transforming inactive complement proteins into their active forms during activation?

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

    Which of the following is NOT a main method for addressing pathogens by the complement system?

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

    What is the role of epithelial barriers in the immune defense?

    <p>To act as a first line of defense</p> Signup and view all the answers

    Study Notes

    Epithelial Surfaces

    • Epithelial surfaces are the first line of defense against pathogens
    • Tight junctions hold epithelial cells together
    • Mucosal epithelia secrete glycoproteins like mucin, which coat bacteria and wash them away
    • Peristalsis and mechanical movements prevent pathogen attachment
    • Commensal bacteria are beneficial and inhibit pathogen colonization
    • Epithelial cells produce antimicrobial proteins and chemicals like digestive enzymes, bile salts, and fatty acids

    Epithelial Surfaces - Antimicrobial Components

    • Lysozyme is an antimicrobial enzyme found in tears, saliva, and phagocytes that breaks down peptidoglycan in bacterial cell walls
    • Antimicrobial peptides like defensins, cathelicidins, and histatins disrupt cell membranes of bacteria and fungi, as well as the cell envelope of some viruses
    • These peptides are thought to create pores in cell membranes, potentially contributing to pathogen invasion

    Epithelial Surfaces - Carbohydrate-binding Proteins

    • Carbohydrate-binding proteins, known as lectins, bind to peptidoglycan on bacteria and elicit bactericidal effects
    • C-type lectins require calcium (Ca) for carbohydrate recognition

    Complement System

    • The complement system is a major defense mechanism after epithelial barriers are breached
    • It consists of over 30 proteins primarily produced in the liver
    • These proteins circulate in an inactive form
    • Complement activation occurs through three pathways:
      • Classical pathway: Antibody-triggered activation
      • Alternative pathway: Activated by pathogens alone
      • Lectin pathway: Activated by lectin-type proteins

    Complement System - Activation and Function

    • Complement system activation involves proteolysis, whereby proteins are digested to their active form
    • Complement proteins successively cleave and activate one another, known as a cascade reaction
    • Complement proteases are synthesized as inactive pro-enzymes (zymogens) which are activated by proteolytic cleavage
    • The complement system addresses pathogens by
      • Triggering inflammation
      • Facilitating phagocytosis
      • Initiating the membrane attack complex (MAC)

    Induced Responses of Innate Immunity

    • The immune system deploys effector mechanisms tailored to individual pathogens
    • These mechanisms include
      • Cell-mediated mechanisms
      • Humoral mechanisms

    Antibodies

    • Antibodies protect against pathogens and their toxic products
    • They are found in plasma and extracellular fluids (formerly called humors)
    • Antibodies are also known as humoral immunity

    Antibodies - Classes and Functions

    • Antibodies have five classes (or isotypes) based on differences in their constant regions:
      • IgM
      • IgG
      • IgA
      • IgE
      • IgD
    • Each class has specific functional properties

    Antibodies - Neutralization, Opsonization, and Complement Activation

    • Antibodies can neutralize pathogens by blocking their access to cells
    • Antibodies can also opsonize pathogens, coating them and facilitating phagocytosis by phagocytes with Fc receptors
    • Antibodies further lead to the activation of the complement system, which can lyse pathogens

    T Cells

    • T cells are crucial for eliminating intracellular pathogens and contribute to cell-mediated immunity within the adaptive immune response
    • T cells develop in the thymus
    • T cells are classified based on their type of T cell receptor, primarily
      • CD8+ T cells
      • CD4+ T cells
    • CD4 and CD8 act as coreceptors, recognizing different regions of MHC molecules and coordinating T cell responses

    T Cells - MHC Class I and MHC Class II

    • MHC class I and MHC class II molecules present peptides from intracellular and extracellular sources, respectively
    • These peptides are trapped within a groove, forming peptide-MHC complexes which are transported to the cell membrane
    • T cells recognize and interact with these peptide-MHC complexes to initiate immune responses.

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    Description

    Explore the vital role of epithelial surfaces in protecting the body against pathogens. This quiz covers tight junctions, mucosal secretion, and the antimicrobial components like lysozyme and defensins that contribute to immune defense. Test your knowledge on how these elements work together to prevent infections.

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