Adaptive Immunity and Immune System Overview
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Adaptive Immunity and Immune System Overview

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Questions and Answers

What are epitopes?

  • Soluble proteins that inhibit immune responses.
  • The primary source of antibodies produced by B-cells.
  • Large molecules that incapacitate pathogens.
  • Small molecular domains recognized by immune cells. (correct)

    • What characterizes an antigen?

  • It exclusively consists of DNA molecules.
  • It is recognized by the cells of the adaptive immune system. (correct)
  • It can only be a molecule found on the surface of pathogens.
  • It triggers an immediate response without prior exposure.

    • Which immunoglobulin is described as the least abundant in plasma?

  • IgG
  • IgA
  • IgD (correct)
  • IgM

    • What role do monomers of IgD serve in the immune system?

    <p>They act as antigen receptors triggering B-cell activation.</p> Signup and view all the answers

    What are the components that can serve as antigens?

    <p>Soluble molecules and components of intact cells.</p> Signup and view all the answers

    What characterizes adaptive immunity in comparison to innate immunity?

    <p>It is acquired gradually by exposure.</p> Signup and view all the answers

    Which cells become activated in adaptive immunity?

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

    What is the primary function of antigen presenting cells (APCs)?

    <p>To present specific molecules to lymphocytes</p> Signup and view all the answers

    Which organs are classified as primary lymphoid organs?

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

    What is the main role of secondary lymphoid organs?

    <p>Lymphocyte activation and proliferation</p> Signup and view all the answers

    Where is mucosa-associated lymphoid tissue (MALT) primarily located?

    <p>In the digestive and respiratory tracts</p> Signup and view all the answers

    What type of lymphocytes proliferate in the structures of MALT?

    <p>B lymphocytes</p> Signup and view all the answers

    How does the immune system primarily interconnect with the body's tissues?

    <p>Through blood and lymphatic circulation</p> Signup and view all the answers

    What is the primary role of the Fc region of immunoglobulins?

    <p>It is recognized by receptors on basophils and mast cells.</p> Signup and view all the answers

    What is the composition of the antigen-binding site of an antibody?

    <p>One heavy chain and one light chain.</p> Signup and view all the answers

    Which part of the antibody molecule varies widely among different antibody molecules?

    <p>The variable region.</p> Signup and view all the answers

    What occurs to the DNA sequences coding for the antibody regions after B lymphocytes are activated?

    <p>They undergo recombination and rearrangement.</p> Signup and view all the answers

    How many identical light chains and heavy chains are found in antibodies?

    <p>Two identical light chains and two identical heavy chains.</p> Signup and view all the answers

    What is the role of the variable region in immunoglobulins?

    <p>It provides specificity for antigen binding.</p> Signup and view all the answers

    Which of the following statements about immunoglobulins is false?

    <p>The Fc region has a variable amino acid sequence.</p> Signup and view all the answers

    What type of cells can produce and target with immunoglobulins aside from immune cells?

    <p>Certain non-immune cells.</p> Signup and view all the answers

    What is the main function of thymic epithelial cells (TECs) in the thymus?

    <p>Creating a blood-thymus barrier</p> Signup and view all the answers

    Which type of TEC is characterized as squamous and forms a layer joined by desmosomes?

    <p>Squamous TEC</p> Signup and view all the answers

    What mainly defines the role of Hassall corpuscles in the thymus?

    <p>Production of cytokines controlling dendritic cells</p> Signup and view all the answers

    During T-cell maturation in the thymus, what is the significance of the thymic microvasculature?

    <p>It allows mature T lymphocytes to exit into venules</p> Signup and view all the answers

    What occurs during the differentiation of T lymphoblasts in the thymus?

    <p>They recombine TCR variable regions</p> Signup and view all the answers

    Which of the following is NOT a characteristic of the thymus?

    <p>It has a tight layer of TECs surrounding the medulla</p> Signup and view all the answers

    What is the primary purpose of the thymus in the immune system?

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

    Which process is primarily involved in the selective removal of T cells in the thymus?

    <p>Negative selection against self-reactive T cells</p> Signup and view all the answers

    What is the primary purpose of the two-stage selection process of thymocytes?

    <p>To ensure TCRs do not recognize self-antigens</p> Signup and view all the answers

    During which stage do thymocytes first encounter MHC molecules?

    <p>Positive selection</p> Signup and view all the answers

    What role do medullary thymic epithelial cells (TECs) play in negative selection?

    <p>They express high levels of the gene Aire</p> Signup and view all the answers

    What happens to T cells that strongly bind self-antigens during negative selection?

    <p>They undergo apoptosis</p> Signup and view all the answers

    Which type of T cells develops from thymocytes that interact with MHC class I molecules?

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

    What is the basis for central immunotolerance in the thymus?

    <p>Deletion of self-reactive T lymphocytes</p> Signup and view all the answers

    What is the influence of cytokines from Hassall corpuscles in the thymic medulla?

    <p>They help develop regulatory T cells</p> Signup and view all the answers

    How long does the selection process for thymocytes typically last?

    <p>2 weeks</p> Signup and view all the answers

    Study Notes

    Adaptive Immunity

    • Provides specific and slower protection against invading microorganisms
    • Involves B and T lymphocytes
    • Activated by specific molecules from foreign cells presented by Antigen Presenting Cells (APCs)
    • Memory lymphocytes produced for faster responses during repeat exposure

    Immune System

    • Provides defense against infections
    • Composed of leukocytes in all tissues and lymphoid organs
    • Connected through the blood and lymphatic circulation

    Primary Lymphoid Organs

    • Location of initial lymphocyte formation:
      • Thymus
      • Bone marrow

    Secondary Lymphoid Organs

    • Sites of lymphocyte activation and proliferation:
      • Lymph nodes
      • Spleen
      • Peyer patches
      • Appendix

    Mucosa-Associated Lymphoid Tissue (MALT)

    • Immune cells located throughout mucous membranes (digestive, respiratory, urogenital)
    • Proliferating B lymphocytes form small, spherical lymphoid nodules

    Immunoglobulins

    • Multiple target cells and effects
    • Common design:
      • Two identical light chains and two identical heavy chains bound by disulfide bonds
      • Fc region: constant carboxyl-terminal portion of heavy chains; recognized by basophil/mast cell receptors
      • Variable region: first 110 amino acids; vary between antibody molecules
      • Antigen-binding site: composed of variable sections of one heavy and one light chain; DNA sequences coding for these regions rearrange after B lymphocyte activation

    Antigens & Antibodies

    • Antigen: molecule recognized by adaptive immune cells, eliciting a response
    • Epitopes: antigenic determinants; small molecular domains of an antigen recognized by immune cells

    Antibodies

    • Five classes:
      • IgG: most common, crosses placenta, activates complement
      • IgA: found in secretions, protects mucosal surfaces, prevents attachment of pathogens
      • IgM: first antibody produced, activates complement, pentamer
      • IgD: least abundant, bound to B lymphocytes, acts as antigen receptor
      • IgE: involved in allergic reactions and parasitic infections

    Thymus

    • Primary lymphoid organ, site of T-lymphocyte differentiation and selection
    • Removes T cells reacting to self-antigens, crucial for central tolerance
    • 3 types of TECs in the cortex:
      • Squamous TECs: form a layer lining the capsule and surrounding microvasculature; part of the blood-thymus barrier
      • Subcapsular TECs: found beneath the capsule
      • Cortical TECs: abundant in the cortex
    • Medulla contains TECs, macrophages, and associated with unique epithelial cells (TECs)
    • Hassall corpuscles: large aggregates of TECs, sometimes concentrically arranged, unique to the medulla

    Role of Thymus in T-Cell Maturation & Selection

    • T lymphoblasts: in the cortex, proliferate, recombine TCR genes, and express TCR, CD4, and CD8
    • Selection process:
      • Positive selection: TCRs must recognize and bind MHC molecules, occurs in the cortex
      • Negative selection: removal of T cells strongly binding self-antigens, occurs in the medulla
    • Aire gene: expressed by medullary TECs, promotes development of regulatory T cells
    • T cell deletion and peripheral tolerance induced by regulatory T cells is the basis for central and peripheral immunotolerance

    Spleen (Secondary Lymphoid Organ)

    • Filters blood and removes old erythrocytes and platelets
    • White pulp: rich in lymphocytes, containing central arteriole, PALS, and lymphatic nodules
    • Red pulp: composed of cords and sinuses, involved in blood filtering and hemolysis
    • Marginal zone: a transition zone containing macrophages and lymphocytes, important for antigen presentation

    Lymph Nodes (Secondary Lymphoid Organ)

    • Filters lymph and removes antigens
    • Capsule: outer layer of connective tissue
    • Subcapsular sinus: space underneath the capsule, filled with lymph
    • Trabeculae: extensions of the capsule extending into the node
    • Cortex: outer region containing follicles, a site of B lymphocyte proliferation
    • Medulla: inner region containing cords of lymphoid cells, where B and T cells interact

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    Test your understanding of adaptive immunity and the immune system with this comprehensive quiz. Explore topics such as lymphocyte formation, the roles of primary and secondary lymphoid organs, and the functions of immunoglobulins. Perfect for biology students learning about human immunity.

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