IgG Antibody Functions and Characteristics
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What is the primary function of IgG antibodies in the humoral response?

  • Triggering antibody-mediated cytotoxicity
  • Opsonization and enhancing phagocytosis (correct)
  • Activating natural killer cells
  • Neutralizing pathogens

    • In which bodily secretions is IgA predominantly found?

  • Blood
  • Tears, saliva, breastmilk, and mucus (correct)
  • Urine
  • Sweat

    • Which of the following is NOT a function of IgG1 and IgG3 antibodies?

  • Neutralizing pathogens (correct)
  • Triggering antibody-mediated cytotoxicity
  • Activating complement
  • Opsonization

    • What is the primary structure of IgA antibodies?

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

    Which IgG subclass is particularly effective at triggering antibody-mediated cytotoxicity by Natural Killer cells?

    <p>IgG2alpha</p> Signup and view all the answers

    What is the primary difference between IgA and IgG antibodies?

    <p>IgA is primarily found in mucosal surfaces, while IgG is found in blood</p> Signup and view all the answers

    Which co-receptor binds an antigen bound to the complement component C3d?

    <p>CD21</p> Signup and view all the answers

    After the antigen binds to the BCR, what happens to the antigen?

    <p>It is internalized by the B-cell</p> Signup and view all the answers

    What is the function of CD19?

    <p>It is a signal transduction protein</p> Signup and view all the answers

    What happens to the B-cell after the antigen binds to the BCR?

    <p>It increases its expression of co-stimulatory molecules</p> Signup and view all the answers

    CD80/86 binds to which protein on TH cells for T-cell activation?

    <p>CD28</p> Signup and view all the answers

    To which type of T-helper cell does the B-cell present the antigen within germinal centers of a lymphoid follicle?

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

    What is the stage at which immunoglobulin gene recombination begins?

    <p>Pro-B cell stage</p> Signup and view all the answers

    What is the function of Ig-α in the B-cell receptor?

    <p>Associates with intracellular signaling molecules</p> Signup and view all the answers

    What happens to a pre-B cell if its BCR is unproductive?

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

    Where do immature B cells travel to after maturation?

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

    What is the purpose of the second checkpoint during B-cell development?

    <p>To check for self-reactivity of the BCR</p> Signup and view all the answers

    What is the role of stromal cells in the bone marrow?

    <p>They allow for communication with B cells through surface markers</p> Signup and view all the answers

    What is the result if a pre-B cell's BCR is self-reactive at the second checkpoint?

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

    What is the type of B cell that leaves the bone marrow?

    <p>Immature transitional B cell</p> Signup and view all the answers

    What is the primary mechanism of neutralization by antibodies?

    <p>Antibody binds to pathogen or toxin, inactivating and preventing binding to cells</p> Signup and view all the answers

    What is the result of the co-stimulatory interaction between iCOSL and iCOS during B-cell activation?

    <p>Production of cytokines by the Tfh cell</p> Signup and view all the answers

    Which of the following antibody functions promotes clearance of pathogens?

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

    What is the primary function of plasma cells?

    <p>Antibody secretion</p> Signup and view all the answers

    What is the role of IgM in the primary immune response?

    <p>It is the first class of antibody secreted during the primary immune response</p> Signup and view all the answers

    During the late primary response, what process results in the production of high-affinity antibodies?

    <p>Somatic hypermutation</p> Signup and view all the answers

    Which of the following antibody functions involves the activation of Fc receptor on Natural killer cells?

    <p>Antibody-dependent cell-mediated cytotoxicity</p> Signup and view all the answers

    What is the role of IL-21 in B-cell activation?

    <p>Proliferation and differentiation of B-cells</p> Signup and view all the answers

    What is the purpose of complement activation by antibodies?

    <p>To initiate the classical pathway of the complement system</p> Signup and view all the answers

    What is the result of antibody class switching?

    <p>Production of antibodies of different classes</p> Signup and view all the answers

    Which of the following antibody classes is characterized by its ability to activate complement?

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

    What is the initial affinity of antibodies produced during the early primary response?

    <p>Medium-affinity</p> Signup and view all the answers

    What is the typical structure of IgM when it is secreted?

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

    Which of the following is a characteristic of IgM's antigen binding?

    <p>Low affinity</p> Signup and view all the answers

    What is the primary function of IgE antibodies?

    <p>Triggers degranulation of granulocytes</p> Signup and view all the answers

    Which type of cells do IgD antibodies primarily bind to?

    <p>Basophils and mast cells</p> Signup and view all the answers

    What is the primary characteristic of IgE antibodies?

    <p>Triggers degranulation of granulocytes</p> Signup and view all the answers

    Where are IgD antibodies primarily found?

    <p>Upper respiratory tract</p> Signup and view all the answers

    What is the primary function of IgD antibodies?

    <p>Binds to basophils and mast cells</p> Signup and view all the answers

    What happens when IgE antibodies bind to cells with Fc receptor?

    <p>Triggers degranulation of granulocytes</p> Signup and view all the answers

    What type of cells does IgE primarily bind to?

    <p>Basophils, mast cells, and eosinophils</p> Signup and view all the answers

    What is the primary function of IgE antibodies in terms of granulocytes?

    <p>Triggers degranulation of granulocytes</p> Signup and view all the answers

    During B-cell development, which checkpoint ensures that immature B cells that recognize self-antigens are eliminated?

    <p>Second checkpoint</p> Signup and view all the answers

    What is the primary function of the paracortex in the lymph node?

    <p>B-cell activation and differentiation</p> Signup and view all the answers

    During B-cell activation, what is the primary role of Th cells?

    <p>Providing co-stimulatory signals to B cells</p> Signup and view all the answers

    What is the result of somatic hypermutation in B cells?

    <p>Increased antibody affinity</p> Signup and view all the answers

    During antibody class switching, which class of antibodies is typically produced in a secondary immune response?

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

    What is the primary location where B cells undergo differentiation into plasma cells or memory cells?

    <p>Germinal center</p> Signup and view all the answers

    What is the primary mechanism by which IgG antibodies facilitate phagocytosis?

    <p>By binding to the Fc receptor on phagocytes, enhancing phagocytosis</p> Signup and view all the answers

    Which of the following IgG subclasses is NOT involved in activating the complement system?

    <p>IgG4</p> Signup and view all the answers

    What is the primary function of IgA antibodies found in blood?

    <p>Neutralizing pathogens</p> Signup and view all the answers

    What is the primary difference between IgA and IgG antibodies in terms of their structures?

    <p>IgA is a dimer, while IgG is a monomer</p> Signup and view all the answers

    Which of the following IgG subclasses is involved in triggering antibody-mediated cytotoxicity by Natural Killer cells?

    <p>IgG2alpha</p> Signup and view all the answers

    Which co-receptor is expressed on the immature B cell in the spleen?

    <p>CD21</p> Signup and view all the answers

    What is the primary component of the BCR on the mature but naive B cell in the spleen?

    <p>IgD and IgM</p> Signup and view all the answers

    What is the primary function of the follicular dendritic cells in the lymph node?

    <p>Presenting antigens to B cells</p> Signup and view all the answers

    What is the primary region of the lymph node where antigen presentation occurs?

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

    Which type of cells are predominantly found in the paracortex of the lymph node?

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

    What is the primary function of the medulla in the lymph node?

    <p>Antibody production</p> Signup and view all the answers

    How do antigens flow into a lymph node?

    <p>Through afferent lymphatics</p> Signup and view all the answers

    What is the primary function of dendritic cells in the periphery?

    <p>Presenting antigens to T cells</p> Signup and view all the answers

    What is the primary function of the BCR in the germinal center?

    <p>To present the antigen to follicular dendritic cells</p> Signup and view all the answers

    What determines the specificity of an antibody?

    <p>The variable region of the light chain</p> Signup and view all the answers

    What is the primary function of plasma cells?

    <p>To secrete a large number of antibody molecules</p> Signup and view all the answers

    What is the characteristic of memory B cells that distinguishes them from naive B cells?

    <p>They are longer-lived than naive B cells</p> Signup and view all the answers

    What is the result of somatic hypermutation in the germinal center?

    <p>The selection of high-affinity antibodies</p> Signup and view all the answers

    What is the primary function of the variable region of the heavy chain?

    <p>To determine the specificity of the antibody</p> Signup and view all the answers

    What is the primary function of memory B cells?

    <p>To proliferate and differentiate into plasma cells upon antigen re-encounter</p> Signup and view all the answers

    What is the purpose of the germinal center in the humoral response?

    <p>To select high-affinity antibodies</p> Signup and view all the answers

    Study Notes

    Antibody Functions

    • Antibodies are good at agglutinating pathogens, immobilizing them, and allowing for phagocytosis
    • Antibody classes:
      • IgG: most common antibody found in serum, has various subclasses (IgG1, IgG2, IgG3, IgG4), secreted as a monomer, produced later in humoral response
      • Functions: opsonization, activating complement, and triggering antibody-mediated cytotoxicity by Natural Killer cells
      • IgA: predominantly found as a dimer, secreted into tears, saliva, breastmilk, and mucus, functions in neutralizing and agglutinating pathogens
      • Can also be found in blood as a monomer with similar functions to IgG

    B-Cell Development

    • B cells develop from common lymphoid precursors into Pre-pro B cells in the bone marrow
    • B cells become irreversibly committed to the B-cell lineage at the pro-B cell stage, where immunoglobulin gene recombination begins
    • As B cells mature, their surface markers change, allowing for communication with stromal cells in the bone marrow
    • The B-cell receptor (BCR) is a membrane-bound antibody that associates with a disulfide-linked heterodimer (Ig-α & Ig-β)

    B-Cell Activation

    • Antigen binds to the BCR with the help of a B-cell co-receptor (CD21) and initiates a downstream signaling cascade promoting B-cell survival and proliferation
    • The antigen is presented to the B cell, which increases its expression of co-stimulatory molecules (CD80/86, iCOSL, CD40)
    • The B cell presents the antigen to a T-helper cell within germinal centers of a lymphoid follicle, leading to the formation of an immunologic synapse

    Antibody Production

    • After interaction with a Tfh cell, some B-cells differentiate into plasma cells for antibody secretion
    • Some B-cells move into germinal centers of lymphoid follicles, where they undergo antibody class switching, somatic hypermutation, and production of high-affinity antibodies

    Antibody Classes and Functions

    • There are 5 main classes of antibodies: IgM, IgG, IgD, IgE, and IgA
    • General antibody functions include:
      • Neutralization: inactivating pathogens and preventing binding to cells
      • Agglutination: preventing pathogen binding to cells and promoting clearance
      • Opsonization: promoting phagocytosis
      • Complement activation: initiating the classical pathway and promoting phagocytosis
      • Antibody-dependent cell-mediated cytotoxicity: activating Natural Killer cells and inducing apoptosis of infected cells
      • Degranulation: activating Fc granulocytes and triggering degranulation

    Antibody Classes

    • IgG: most common antibody found in serum, secreted as a monomer, produced later in the humoral response
      • Functions: opsonization, binding to Fc receptor on phagocytes to enhance phagocytosis, IgG1 and IgG3 activate complement, IgG2alpha triggers antibody-mediated cytotoxicity by Natural Killer cells
    • IgA: predominantly found as a dimer, secreted into tears, saliva, breastmilk, and mucus
      • Functions: neutralizing pathogens, agglutinating pathogens, inducing degranulation of granulocytes
    • IgE: secreted as a monomer in small quantities, binds to cells with Fc receptor for IgE triggering degranulation of granulocytes (eosinophils, basophils, mast cells)
    • IgD: secreted as a monomer in very small quantities, most prevalent in secretions of the upper respiratory tract, binds to basophils and mast cells

    B-Cell Development and Activation

    • B-cell development stages in bone marrow:
      • Stages: pro-B, large pre-B, small pre-B, immature B, mature B
    • Two checkpoints in bone marrow:
      • Checkpoint 1: after pro-B stage, ensures proper rearrangement of heavy chain genes
      • Checkpoint 2: after small pre-B stage, ensures proper rearrangement of light chain genes
    • B-cell development after bone marrow:
      • Immature B cells migrate to spleen, where they express CD21 and IgD, and are considered mature but naive
      • Mature naive B cells enter general circulation, then migrate to lymph nodes
    • B-cell activation:
      • Naive B cells encounter antigen in lymph node through one of two ways:
        • Antigen flows into lymph node through afferent lymphatics and binds to BCR
        • Macrophages or dendritic cells encounter antigen in periphery and bring it to lymph node
      • Antigen recognition leads to B-cell activation, which requires three signals:
        • Signal 1: antigen binding to BCR
        • Signal 2: co-stimulation by CD40 and CD40L
        • Signal 3: cytokine stimulation by Tfh cells

    Lymph Node Structure and Function

    • Lymph nodes are bean-shape structures with three main regions:
      • Cortex: contains lymphocytes, macrophages, and follicular dendritic cells, arranged into primary follicles that enlarge into secondary follicles with germinal centers after antigen exposure
      • Paracortex: contains mostly T-lymphocytes and dendritic cells, which present antigens to T-helper cells
      • Medulla: more sparsely populated with lymphoid-linage cells, often plasma cells actively secreting antibody molecules

    B-Cell Activation and Differentiation

    • B-cell activation leads to differentiation into plasma cells or memory B cells
    • Plasma cells:
      • No longer have BCR, secrete large numbers of antibody molecules
    • Memory B cells:
      • Circulate in periphery, continue to express BCR, longer-lived than naive B-cells
      • Differentiation into memory B cells is unclear

    Antibody Structure and Function

    • Antibody structure: protein molecules with two heavy chains and two light chains
      • Heavy chain: constant region (Fc) and variable region (Fab)
      • Light chain: variable region and antigen-binding portion
    • Antibody functions: six categories:
      • Neutralizing pathogens
      • Agglutinating pathogens
      • Opsonization
      • Complement activation
      • Antibody-mediated cytotoxicity
      • Inducing degranulation of granulocytes

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    Learn about the functions and characteristics of IgG antibodies, including their role in opsonization, production, and classes. Understand their importance in the humoral response.

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