Lec 7 Quiz
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Questions and Answers

How do antibodies achieve specificity in recognizing specific epitopes on an antigen?

  • Through interactions with the constant regions of the heavy chains, which vary greatly between antibodies.
  • Via the hinge region that allows flexibility to accommodate different antigen shapes.
  • Through the process of somatic hypermutation within the constant regions, altering the antibody's general affinity over time.
  • By using antigen binding sites on the variable regions of the light and heavy chains, particularly the hypervariable regions (CDR1-3). (correct)

    • What is the primary role of the hinge region in IgG, IgD, and IgA antibodies?

  • To facilitate complement activation.
  • To mediate interactions with immune cells via Fc receptors.
  • To provide structural support for the constant region.
  • To enable flexibility, allowing the antibody to bind to epitopes at varying angles and distances. (correct)

    • How do RSSs (recombination signal sequences) and RAG (recombination-activating genes) contribute to the diversity of B-cell receptors (BCRs) and antibodies?

  • RSSs promote somatic hypermutation in mature B cells, and RAG genes enhance this process in the germinal center.
  • RSSs directly encode the variable regions of antibodies, while RAG genes modify these regions post-transcriptionally.
  • RSSs inhibit gene transcription outside of the variable region, while RAG genes enhance transcription within the variable region.
  • RSSs guide somatic recombination by flanking gene segments, and RAG genes mediate the cutting and joining of DNA segments. (correct)

    • During the generation of junctional diversity, which enzyme is responsible for the addition of N-nucleotides?

    <p>TdT (terminal deoxynucleotidyl transferase) (D)</p> Signup and view all the answers

    Which mechanism of antibody-mediated combatting of infection, enhances phagocytosis by coating the pathogen to promote recognition and ingestion by phagocytes?

    <p>Opsonization (B)</p> Signup and view all the answers

    Which of the following is the primary distinction between the roles of IgG1 and IgG4?

    <p>IgG1 is better at sensitizing mast cells compared to IgG4. (B)</p> Signup and view all the answers

    If a patient lacks the ability to produce the enzyme AID, which of the following immune processes would be directly impaired?

    <p>Somatic hypermutation and class switching. (B)</p> Signup and view all the answers

    A researcher is studying the immune response in mucosal tissues. Which antibody form would they most likely find in abundance in these areas?

    <p>Dimeric IgA (B)</p> Signup and view all the answers

    How does alternative splicing contribute to B-cell function?

    <p>It differentiates between membrane-bound BCRs and secreted antibodies. (B)</p> Signup and view all the answers

    Which step in the antibody production process is both reversible and regulated, allowing for dynamic adjustments in the immune response?

    <p>The switch from membrane Ig to secreted antibody (C)</p> Signup and view all the answers

    What is the significance of junctional diversity in antibody production?

    <p>It increases the variability in antibody sequences. (A)</p> Signup and view all the answers

    Considering their effector functions, which antibody would be most effective against a systemic bacterial infection?

    <p>IgG1 (C)</p> Signup and view all the answers

    During an infection, if a B cell initially produces IgM, what mechanism allows it to later produce IgG1 antibodies specific to the same antigen?

    <p>Class switching (A)</p> Signup and view all the answers

    Which antibody class is MOST effective at directly triggering the classical complement pathway?

    <p>IgM (D)</p> Signup and view all the answers

    Which process is irreversible once it occurs in a B cell?

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

    Flashcards

    Epitopes

    Specific regions on an antigen recognized by antibodies.

    Hinge region of antibodies

    Flexible part of IgG, IgD, and IgA classes allowing movement.

    Hypervariable regions

    Regions in antibodies that determine specificity for epitopes.

    RAG genes

    Recombination-activating genes essential for B and T cell diversity.

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    Junctional diversity

    Process creating additional diversity in antibodies beyond gene segments.

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    IgA

    An antibody found in monomeric and dimeric forms; secreted into mucosal surfaces.

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    IgM

    An antibody that can exist as a monomer on cell surfaces or as secreted pentamers.

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    IgG subclass functions

    IgG1, IgG2, IgG3, and IgG4 have roles in neutralization, opsonization, and placental transfer.

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    Somatic hypermutation

    A process enabling B cells to alter their immunoglobulin genes post-activation, enhancing antibody affinity.

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    Antibody class switching

    The process where B cells change antibody type, such as from IgM to IgG, via DNA recombination.

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    BCR vs. Antibody

    B cells produce membrane-bound BCR or secreted antibodies via alternative splicing.

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    Reversible antibody production stages

    Stages like RNA splicing for antibody synthesis are reversible, allowing flexibility.

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    Irreversible antibody production stages

    Stages like somatic recombination and somatic hypermutation are permanent alterations.

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    Activation-induced cytidine deaminase (AID)

    An enzyme involved in somatic hypermutation, crucial for B cell proliferation.

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    Multimeric antibodies

    IgM and IgA can form multimers, allowing them to function effectively in immune response.

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    Study Notes

    Antibody Recognition of Epitopes

    • Antibodies recognize specific epitopes, localized regions on antigens that trigger immune responses.

    Antibody Hinge Region

    • The hinge region is found only in IgG, IgD, and IgA antibodies.
    • Its function isn't specified.

    Hypervariable Regions (HV1-HV3 or CDR1-3)

    • The antibody's antigen-binding site, in the variable regions of light and heavy chains, determines epitope recognition.
    • Amino acid sequences in these regions dictate specificity.
    • Diversity in these regions creates different antibody specificities.

    RSSs and RAG Genes

    • RSSs (recombination signal sequences) guide somatic recombination of gene segments.
    • RAG (recombination-activating genes) are crucial in B and T cell development, orchestrating this process.

    Junctional Diversity

    • Junctional diversity creates further antibody diversity beyond the gene segments.
    • The RAG complex cleaves RSSs, creating DNA hairpins that RAG opens.
    • P-nucleotides form from nicks in the DNA strands.
    • TdT adds N-nucleotides, and exonucleases remove unpaired nucleotides.
    • Coding ends are synthesized and joined, creating varied antibody combinations.
    • Not all junctional diversity events yield a functional BCR.

    Antibody Mechanisms Against Infections

    • Antibodies combat infections through several mechanisms, including:
      • Classical pathway (complement activation)
      • Neutralization (preventing pathogen binding)
      • Opsonization (enhancing phagocytosis)

    Antibody Classes and Functions

    • IgG, IgA are further divided into subclasses (IgG1-4, IgA1, IgA2).

    • IgM exists as a membrane-bound monomer or secreted pentamer.

    • IgA exists as a monomer or dimer (secreted to mucosal surfaces).

    • Each class has different roles in immunity, including neutralization, opsonization, complement activation, and transport.

    • Specific roles for different Antibody classes:

      • IgM: Neutralization, complement activation, transport.
      • IgG1: Neutralization, opsonization, NK cell activation, mast cell sensitization, complement activation, placental transport.
      • IgG2: Neutralization, complement activation, placental transport.
      • IgG3: Neutralization, opsonization, NK cell activation, mast cell sensitization, complement activation, placental transport.
      • IgG4: Neutralization, opsonization, placental transport.
      • IgA: Neutralization, opsonization, complement activation, mucosal transport.
      • IgE: Mast cell sensitization.

    Antibody Forms

    • IgM and IgA can form multimers.

    Somatic Hypermutation

    • Somatic hypermutation occurs after B-cell antigen activation.
    • It targets the rearranged variable region gene segment.
    • Activation-induced cytidine deaminase (AID) is the key enzyme.
    • AID converts cytidine to uridine, which DNA repair enzymes alter.
    • This process diversifies antibodies, enhancing affinity.

    Antibody Class Switching

    • Class switching involves recombination of specific DNA regions.
    • IgM and IgD are initially produced.
    • AID targets switch regions (e.g., Su, Sy1).
    • DNA strands recombine to switch to other classes (e.g., IgG1).

    B Cell Production of IgM vs. IgD

    • B cells initially produce both IgM and IgD. (Co-expression)

    BCR vs. Antibody Production

    • Alternative splicing determines the membrane-bound (BCR) or secreted (antibody) form.

    Reversible vs. Irreversible Antibody Production Stages

    • V-region assembly, junctional diversity, and transcriptional controlling elements are irreversible.
    • Antibody production's steps involving membrane Ig to secreted antibody and somatic hypermutation are regulated and reversible.

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