B-Cell Mediated Immunity II
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Questions and Answers

What binds to CD40 on B cells to activate NFκB?

  • LFA-1 on TFH cells
  • CD40 ligand from TFH cells (correct)
  • MHC-II:peptide complexes
  • Cytokines from B cells

    • What is the primary role of ICAM-1 in the interaction between B cells and TFH cells?

  • To activate NFκB in TFH cells
  • To present antigen to TFH cells
  • To bind LFA-1 on TFH cells (correct)
  • To increase recognition by TCR

    • What transcription factor is required for the differentiation of plasmablasts into plasma cells?

  • TCR
  • IL-5
  • BLIMP1 (correct)
  • NFκB

    • Which of the following correctly describes the function of TFH cells in relation to B cells?

    <p>They deliver cytokines directly onto B cells.</p> Signup and view all the answers

    Where do cognate pairs of B cells and TFH cells primarily move to during clonal expansion?

    <p>Medullary cords</p> Signup and view all the answers

    What type of antigens are classified as 'thymus-independent' (TI) antigens?

    <p>Antigens that do not require T cell help for activation</p> Signup and view all the answers

    Which characteristic is NOT associated with thymus-independent (TI) antigens?

    <p>Dependence on T cells for activation</p> Signup and view all the answers

    What type of antibodies are primarily produced in response to TI antigens?

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

    What type of antigens are commonly recognized by the antibodies produced against thymus-independent antigens?

    <p>Common bacterial polysaccharides</p> Signup and view all the answers

    Which B cell population is more likely to express CD5?

    <p>B-1 cells</p> Signup and view all the answers

    What type of cells do immature B cells develop into during positive selection?

    <p>Memory B cells</p> Signup and view all the answers

    Which characteristic distinguishes a mature B cell from an immature B cell?

    <p>Higher expression of IgD</p> Signup and view all the answers

    What is the main role of the negative selection process in B cell development?

    <p>To eliminate self-reactive B cells</p> Signup and view all the answers

    What triggers the proliferation of B cells into clones upon activation?

    <p>Recognition of foreign antigen</p> Signup and view all the answers

    Where do immature B cells mature after leaving the bone marrow?

    <p>Secondary lymphoid tissues</p> Signup and view all the answers

    Which type of immunity involves the activation of B cells?

    <p>Adaptive Immunity</p> Signup and view all the answers

    What is the main function of plasma cells produced from activated B cells?

    <p>To produce antibodies</p> Signup and view all the answers

    What aspect is essential for B cell receptor (BCR) diversity?

    <p>Genetic rearrangement during development</p> Signup and view all the answers

    What role does Bcl-xL play in centrocytes?

    <p>Inhibits apoptosis</p> Signup and view all the answers

    What triggers the activation of centrocytes following antigen interaction?

    <p>Cross-linking of BCRs by antigen</p> Signup and view all the answers

    Which gene expression is necessary for isotype switching in B cells?

    <p>AID gene</p> Signup and view all the answers

    What happens to centrocytes that do not successfully internalize antigen?

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

    Which enzyme is NOT involved in isotype switching?

    <p>CD40L</p> Signup and view all the answers

    What is the effect of IL-21 in B-cell differentiation?

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

    What is a characteristic of the Hyper-IgM Syndrome related to the AID gene?

    <p>Production of low-affinity IgM antibodies</p> Signup and view all the answers

    Isotype switching can occur between which regions?

    <p>Any two switch regions</p> Signup and view all the answers

    Which cytokines control the pattern of isotype switching in B cells?

    <p>Cytokines released by effector TFH cells</p> Signup and view all the answers

    What is the primary outcome when newly activated B cells encounter specific antigens?

    <p>They form cognate pairs with effector T follicular helper cells.</p> Signup and view all the answers

    Which process connects rearranged variable-region exons with different heavy-chain constant region exons?

    <p>Isotype switching</p> Signup and view all the answers

    Which phase describes the expansion of activated B cells that migrate to form secondary follicles?

    <p>Secondary clonal expansion</p> Signup and view all the answers

    What role do follicular dendritic cells (FDCs) play in B cell maturation?

    <p>They store and display intact antigens for B cell recognition.</p> Signup and view all the answers

    What occurs during isotype switching in activated B cells?

    <p>They produce high affinity antibodies of different classes.</p> Signup and view all the answers

    What initiates intracellular signaling in a mature naive B cell upon antigen binding?

    <p>Cross-linking of BCRs and association of Igα and Igβ.</p> Signup and view all the answers

    How are high-affinity B cell receptors selected during affinity maturation?

    <p>Through antigen-mediated selection in germinal centers.</p> Signup and view all the answers

    Which of the following proteins is NOT part of the B-cell co-receptor complex?

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

    What is the primary role of T follicular helper (TFH) cells in the activation of B cells?

    <p>To secrete cytokines that activate B cells.</p> Signup and view all the answers

    What defines a memory B cell in the context of the immune response?

    <p>It retains high-affinity BCRs and persists long-term.</p> Signup and view all the answers

    What is the effect of deficiency or defects in CD19 or CD81 on B cells?

    <p>Impaired antibody-mediated immunity.</p> Signup and view all the answers

    Which factor is primarily responsible for the generation of iC3b and C3d from C3b on a pathogen's surface?

    <p>Factor I</p> Signup and view all the answers

    What distinguishes plasma cells from lymphoblasts in their function?

    <p>Plasma cells primarily secrete antibodies.</p> Signup and view all the answers

    What is the key mechanism of primary immune response associated with activated B cells?

    <p>They involve isotype switching to produce multiple antibody types.</p> Signup and view all the answers

    What occurs to B cells after they stop dividing and no longer express surface IgM?

    <p>They become unresponsive and do not interact with T cells.</p> Signup and view all the answers

    What is the role of somatic hypermutation in B cell maturation?

    <p>It introduces point mutations in the V domain coding sequence.</p> Signup and view all the answers

    In the germinal center, which cells undergo somatic hypermutation and affinity maturation?

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

    What characterizes the dark zone of the germinal center?

    <p>Densely packed with dividing centroblasts.</p> Signup and view all the answers

    What is the main function of the enzyme activation-induced cytidine deaminase (AID) in B cells?

    <p>To create point mutations during transcription.</p> Signup and view all the answers

    What is primarily produced during affinity maturation?

    <p>Antibodies of progressively higher affinity for the antigen.</p> Signup and view all the answers

    How do centrocytes with high-affinity BCRs compete with others in the germinal center?

    <p>Through cross-linking with antigenic peptides.</p> Signup and view all the answers

    Which statement about B cells in the germinal center is incorrect?

    <p>Mantle zone is composed of divided centrocytes.</p> Signup and view all the answers

    What is the effect of interleukins secreted by FDCs in the germinal center?

    <p>They stimulate resting B cells to divide.</p> Signup and view all the answers

    What defines the mantle zone in the germinal center?

    <p>Houses naïve B cells searching for specific antigens.</p> Signup and view all the answers

    During clonal expansion, what happens to B lymphoblasts in response to antigen and T-cell cytokines?

    <p>They undergo division and differentiate into plasma cells.</p> Signup and view all the answers

    What is the role of TFH cells in the germinal center?

    <p>To bind to centrocytes and provide survival signals.</p> Signup and view all the answers

    What distinguishes the light zone from the dark zone in the germinal center?

    <p>Centrocytes in the light zone exhibit slower division.</p> Signup and view all the answers

    What leads to a massive increase in mutation rate in B cells during somatic hypermutation?

    <p>Enhanced enzyme production.</p> Signup and view all the answers

    What is the effect of mutated and isotype-switched surface Ig on centrocytes?

    <p>They facilitate competition for T cell interactions.</p> Signup and view all the answers

    Study Notes

    B-Cell Mediated Immunity II

    • B cells are generated in the bone marrow with diverse B cell receptors (BCRs).
    • Immature B cells undergo negative selection to eliminate self-reactive B cells.
    • Positive selection promotes the maturation of a subset of immature B cells.
    • Mature B cells (naïve B cells) circulate throughout the body, searching for their specific antigen.
    • Upon specific antigen encounter, B cells form a cognate pair with a previously activated helper T cell (TFH cell).
    • Activated B cells proliferate and differentiate into plasma cells and memory B cells in germinal centers.
    • Newly activated B cells have two fates: some differentiate into IgM-secreting plasma cells, then move to medullary cords (primary clonal expansion).
    • Other B cells migrate to the primary follicle to form a secondary follicle, creating a germinal center (secondary clonal expansion).
    • In the germinal center, further differentiation occurs, including isotype switching and affinity maturation.
    • Follicular dendritic cells (FDCs) play a crucial role in antigen presentation and B cell maturation within the germinal center.

    B Cell Receptor Complex

    • The BCR complex consists of membrane-bound immunoglobulins (IgM and IgD) and the Igα/Igβ protein complex.
    • Igα/Igβ links the Ig molecules to intracellular signaling pathways.
    • ITAMS (immunoreceptor tyrosine-based activation motifs) within Igα and Igβ are crucial for signal transduction.

    B Cell Co-Receptor

    • The B cell co-receptor consists of three proteins: CR2 (complement receptor 2), CD19, and CD81.
    • The co-receptor enhances B cell activation by binding to fragments of complement proteins.
    • Deficiencies in CD19 or CD81 impair the antibody-mediated immune response.

    Complement Receptors

    • Complement receptors (CRs) play a role in antigen capture and presentation.
    • iC3b and C3d are bound by CRs, facilitating interactions with B cells.
    • This interaction enhances B cell activation through a co-receptor mechanism.

    Follicular Dendritic Cells (FDCs)

    • Organize B cell areas into primary follicles and display intact antigens on their surface.
    • FDCs are crucial for B cell maturation, survival, and antibody responses.
    • They display antigens from the circulation, lymph, or directly from pathogens.

    Naïve B Cells

    • Naïve B cells circulate, searching for antigen in the secondary lymphoid organs.
    • CCL21 and CCL19 chemokines attract B cells to the T cell zone.
    • CXCL13 chemokine attracts B cells to the B cell area of the follicle.
    • Antigen-activated B cells migrate to the boundary between B and T cell zones.

    Activation of Naïve B Cells

    • Cross-linking of BCRs by antigen triggers intracellular signals via Igα/Igβ.
    • Co-receptor binding to complement fragments further enhances activation.
    • Interaction with TFH cells is necessary for full B cell activation.

    Clonal Expansion: Primary/Secondary Focus

    • Primary focus for B cell expansion occurs in medullary cords.
    • Secondary focus occurs in the germinal center of the primary follicle, followed by centrocyte formation and somatic hypermutation.

    Germinal Center

    • Centroblasts are rapidly dividing B cells in the germinal center dark zone.
    • Centrocytes differentiate from centroblasts in the light zone, where they undergo somatic hypermutation.
    • FDCs and TFH cells in the germinal center select centrocytes with high-affinity BCRs.

    Somatic Hypermutation

    • AID (activation-induced cytidine deaminase) is crucial for introducing point mutations in V-region genes of B cells during germinal center reactions.
    • Increases affinity of BCRs for antigen.

    Affinity Maturation

    • Generating B cell clones exhibiting progressively higher antigen-binding affinities through somatic hypermutation.
    • High-affinity BCRs are selected, while low-affinity B cells die via apoptosis.

    Isotype Switching

    • Recombination of variable (V) and constant (C) regions of the immunoglobulin heavy chain gene to switch antibody isotype.
    • Enables production of antibodies with different effector functions based on the needs of the immune system.

    High-Affinity BCR Centrocytes

    • Generated through somatic hypermutation and selected by interactions with TFH cells and FDCs.
    • High-affinity BCRs are critical for mounting a strong and effective antibody response.

    Low-Affinity BCR Centrocytes

    • Centrocytes with low-affinity BCRs frequently undergo apoptosis.
    • The process ensures a shift towards higher antibody affinity.

    Plasma Cells/Memory B Cells

    • Plasma cells produce antibodies and have a function related to "fighting the current infection".
    • Memory B cells are crucial for a rapid response during future exposures to the same antigen (useful for future infections).

    B-1 Cells

    • A subset of B cells that are mostly produced during fetal development.
    • Respond to T-independent antigens, generating low-affinity IgM antibodies.
    • Do not undergo affinity maturation or isotype switching.

    Hyper-IgM Syndrome

    • A genetic deficiency characterized by the inability to perform somatic hypermutation and isotype switching.
    • Results in a production of low affinity IgM antibodies, and increased susceptibility to infections.

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    B-Cell Mediated Immunity II PDF

    Description

    Dive into the intricacies of B-cell mediated immunity with this quiz covering their development, selection, and activation. Explore how B cells interact with helper T cells and differentiate into plasma and memory cells, emphasizing processes like isotype switching and affinity maturation. Test your understanding of this vital aspect of the immune system.

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