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Questions and Answers
What role do tight junctions between epithelial cells serve in the immune defense?
What role do tight junctions between epithelial cells serve in the immune defense?
Which of the following are antimicrobial peptides mentioned in the immune defense?
Which of the following are antimicrobial peptides mentioned in the immune defense?
What is the primary function of lysozyme in the immune response?
What is the primary function of lysozyme in the immune response?
Which aspect of mucosal epithelia contributes to preventing bacterial attachment?
Which aspect of mucosal epithelia contributes to preventing bacterial attachment?
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How do C-type lectins contribute to the immune defense?
How do C-type lectins contribute to the immune defense?
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What is one consequence of environmental stressors like drought on epithelial barriers?
What is one consequence of environmental stressors like drought on epithelial barriers?
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What are the primary mechanisms by which epithelial cells deter pathogen invasion?
What are the primary mechanisms by which epithelial cells deter pathogen invasion?
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What is the significance of commensal bacteria in the context of epithelial barriers?
What is the significance of commensal bacteria in the context of epithelial barriers?
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What is a primary function of antibodies in relation to pathogens?
What is a primary function of antibodies in relation to pathogens?
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Which effector mechanism specifically facilitates phagocytosis?
Which effector mechanism specifically facilitates phagocytosis?
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What distinguishes the two main classes of T cells?
What distinguishes the two main classes of T cells?
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How does the complement system primarily function in immune defense?
How does the complement system primarily function in immune defense?
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Where do T-cells develop in the human body?
Where do T-cells develop in the human body?
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What mechanism is used by antibodies to prevent viruses from entering host cells?
What mechanism is used by antibodies to prevent viruses from entering host cells?
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What are the specific receptors called that T-cells use to recognize peptide:MHC complexes?
What are the specific receptors called that T-cells use to recognize peptide:MHC complexes?
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Which type of immunity is primarily mediated by antibodies?
Which type of immunity is primarily mediated by antibodies?
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Which pathway of complement activation is triggered specifically by the presence of antibodies?
Which pathway of complement activation is triggered specifically by the presence of antibodies?
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What is the initial step in the activation of complement proteins?
What is the initial step in the activation of complement proteins?
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What is the primary function of membrane attack in the complement system?
What is the primary function of membrane attack in the complement system?
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How are most proteins of the complement system produced?
How are most proteins of the complement system produced?
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Which mechanism of the complement system does NOT require the presence of antibodies for activation?
Which mechanism of the complement system does NOT require the presence of antibodies for activation?
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What process is involved in transforming inactive complement proteins into their active forms during activation?
What process is involved in transforming inactive complement proteins into their active forms during activation?
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Which of the following is NOT a main method for addressing pathogens by the complement system?
Which of the following is NOT a main method for addressing pathogens by the complement system?
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What is the role of epithelial barriers in the immune defense?
What is the role of epithelial barriers in the immune defense?
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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.
