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Questions and Answers
What is the role of memory cells in the immune response?
What is the role of memory cells in the immune response?
Which of the following best describes affinity in the context of antibodies?
Which of the following best describes affinity in the context of antibodies?
What type of antibodies are primarily secreted by plasma cells?
What type of antibodies are primarily secreted by plasma cells?
What distinguishes T-dependent antigens from T-independent antigens?
What distinguishes T-dependent antigens from T-independent antigens?
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Which process occurs after the activation of B lymphocytes?
Which process occurs after the activation of B lymphocytes?
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What role do T helper cells play in the B lymphocyte response to antigens?
What role do T helper cells play in the B lymphocyte response to antigens?
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Which type of B cell is primarily responsible for T-dependent immune responses?
Which type of B cell is primarily responsible for T-dependent immune responses?
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What happens when a B lymphocyte captures and processes peptide antigens?
What happens when a B lymphocyte captures and processes peptide antigens?
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What molecule enhances B cell activation through simultaneous engagement with C3D and antigen?
What molecule enhances B cell activation through simultaneous engagement with C3D and antigen?
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Which type of receptor does TLR represent in innate immunity?
Which type of receptor does TLR represent in innate immunity?
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What is a major difference between T-dependent and T-independent antigen responses?
What is a major difference between T-dependent and T-independent antigen responses?
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What is NOT one of the proteins expressed by B cells upon activation?
What is NOT one of the proteins expressed by B cells upon activation?
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Which type of antigens do subsets of B cells respond to preferentially?
Which type of antigens do subsets of B cells respond to preferentially?
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Where are naive B cells activated by protein antigens?
Where are naive B cells activated by protein antigens?
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What is the function of the MHC II molecule on B lymphocytes?
What is the function of the MHC II molecule on B lymphocytes?
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Which statement about the qualitative changes of B lymphocytes is true?
Which statement about the qualitative changes of B lymphocytes is true?
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What is the main function of helper T cells in relation to B cell activation?
What is the main function of helper T cells in relation to B cell activation?
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Why are T-independent responses considered less effective than T-dependent responses?
Why are T-independent responses considered less effective than T-dependent responses?
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What happens when an antigen binds to a B cell receptor?
What happens when an antigen binds to a B cell receptor?
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Which of the following best describes the relationship between B cells and T cells during activation?
Which of the following best describes the relationship between B cells and T cells during activation?
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Which cytokine receptor is involved in the signaling process of activated B lymphocytes?
Which cytokine receptor is involved in the signaling process of activated B lymphocytes?
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Where are marginal-zone B cells primarily located?
Where are marginal-zone B cells primarily located?
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Which type of antigens do B-1 cells primarily respond to?
Which type of antigens do B-1 cells primarily respond to?
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What triggers B cell activation in conjunction with the binding of antigens?
What triggers B cell activation in conjunction with the binding of antigens?
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What receptors do B lymphocytes express to facilitate their activation?
What receptors do B lymphocytes express to facilitate their activation?
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What is the composition of the B cell receptor (BCR) complex?
What is the composition of the B cell receptor (BCR) complex?
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How does innate immunity assist in B lymphocyte activation?
How does innate immunity assist in B lymphocyte activation?
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What type of antigens are predominantly recognized by polysaccharides and lipids?
What type of antigens are predominantly recognized by polysaccharides and lipids?
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What is the primary function of complement receptor type 2 on B lymphocytes?
What is the primary function of complement receptor type 2 on B lymphocytes?
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Where are B cells primarily located within the lymph node?
Where are B cells primarily located within the lymph node?
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What captures and processes the antigen for T lymphocytes in the lymph node?
What captures and processes the antigen for T lymphocytes in the lymph node?
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What is the role of CCR5 in B lymphocytes?
What is the role of CCR5 in B lymphocytes?
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How do T helper cells interact with B lymphocytes in the lymph node?
How do T helper cells interact with B lymphocytes in the lymph node?
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What facilitates the migration of B lymphocytes towards the paracortex?
What facilitates the migration of B lymphocytes towards the paracortex?
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What is necessary for a B lymphocyte to recognize an antigen?
What is necessary for a B lymphocyte to recognize an antigen?
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Where are T cells located within the lymph node?
Where are T cells located within the lymph node?
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What is the main function of the CCR7 receptor for T lymphocytes?
What is the main function of the CCR7 receptor for T lymphocytes?
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What is the primary function of cytokines produced by follicular helper T cells in isotype switching?
What is the primary function of cytokines produced by follicular helper T cells in isotype switching?
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What step initiates class switching in B lymphocytes?
What step initiates class switching in B lymphocytes?
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Which type of B lymphocyte is primarily responsible for producing IgA?
Which type of B lymphocyte is primarily responsible for producing IgA?
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What is the main role of activation-induced cytidine deaminase (AID) in isotype switching?
What is the main role of activation-induced cytidine deaminase (AID) in isotype switching?
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How does affinity maturation influence B cell response to antigens over time?
How does affinity maturation influence B cell response to antigens over time?
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Study Notes
Humoral Immune Response I
- Humoral immunity is mediated by antibodies (IgM, IgG, IgA, IgE, IgD)
- Antibodies neutralize and eliminate extracellular microbes and microbial toxins
- Secreted antibodies circulate and enter mucosal fluids
- The primary defense mechanism is against microbes with capsules rich in polysaccharides and lipids, which T cells cannot respond to
- B lymphocytes mature in the bone marrow, and T lymphocytes mature in the thymus.
Phases of B Lymphocytes
- B lymphocytes mature in bone marrow; T lymphocytes in thymus
- Mature lymphocytes (naïve) leave the generative lymphoid organs and enter the circulation and peripheral lymphoid organs (lymph nodes, spleen, mucosal lymphoid tissues)
- Naïve B cells encounter antigen, expressing specific receptors.
- B cell activation followed by proliferation and differentiation into plasma cells (antibody-secreting cells) and memory cells (primary response).
- Memory cells survive for extended periods; responding rapidly upon secondary antigen encounter (secondary response).
- B cell activation involves antigen-recognition, then activation and proliferation.
T-dependent and T-independent antigens
- T-dependent antigens: proteins
- T-independent antigens: polymeric antigens, specifically polysaccharides, and glycolipids, nucleic acids.
- T-helper cells play a significant role in T-dependent antigen responses
- T-independent responses produce mainly IgM, characterized by short-lived plasma cells.
- T-dependent antigens produce more qualitatively diverse antibodies, including IgG, IgE, and IgA, and exhibit a longer lifespan
Subsets of B Cells
- Follicular B cells reside in and circulate through lymphoid organ follicles. They produce the bulk of T-dependent, class-switched, and high-affinity antibody responses against protein antigens, resulting in long-lived plasma cells.
- Marginal-zone B cells are found in the splenic white pulp and primarily respond to blood-borne polysaccharide and lipid antigens.
- B-1 cells are located in mucosal tissues and the peritoneum, and primarily respond to non-protein antigens.
B cell Recognition, Activation, and Response to Antigens
- Humoral immune responses are initiated when antigen-specific B lymphocytes in the spleen and lymph nodes recognize antigens using membrane-bound immunoglobulins (IgM and IgD).
- These naïve B lymphocytes have membrane bound IgM and IgD, the antigen receptors with highly variable antigen-binding regions.
- Immunoglobulins (Igs) bind to antigen and activate B cells
- B cell receptor (BCR) complex: Ig + two proteins (Igα and Igβ).
Antigen-Induced Signaling in B cells
- Polysaccharides, lipids, and other non-protein antigens contain multiple identical epitopes, allowing them to cross-link multiple Ig receptors simultaneously.
- Even protein antigens can be expressed on microbes in an array format, enabling cross-linking of Ig receptors on a B cell.
Role of Innate Immune Signals in B Cell Activation
- B lymphocytes express a receptor for C3d (complement receptor type 2), a fragment of complement protein C3.
- Complement activation facilitates B lymphocyte activation.
Microbial products directly activate B cells
- B cells express Toll-like receptor (TLR) on their surface.
- TLR engagement by microbial products triggers activating signals, stimulating B cell proliferation, differentiation.
Activated B Lymphocytes Interaction with T Lymphocytes
- Naive CD4+ T cells are activated in the T-cell zone, differentiating into helper T cells.
- Naive B cells are activated in follicles of the same lymphoid organ.
- Antigen-activated helper T cells and B cells migrate toward each other, interacting at the edges of follicles, where initial antibody response formation occurs.
- Some B cells migrate into follicles to form germinal centers.
Follicular Dendritic cells (FDC)
- FDCs reside in the light zones of germinal centers in peripheral lymphoid organs.
- FDCs display antigens stimulating B cell differentiation.
- They don't present antigens to T cells
Activated B Lymphocyte Development & Germinal Center Reaction
- Activation of B cells leads to migration to germinal centers.
- Somatic mutation and affinity maturation occur, including isotype switching.
- High-affinity antibody-secreting cells and memory B cells are generated and leave the germinal center.
Class Switching
- Helper T cells stimulate progeny B lymphocytes to produce antibodies with different heavy-chain isotypes (IgG, IgA, IgE)
- Class switching, involving a combination of CD40/CD40L signals and cytokines, is determined by the cytokines produced by follicular helper T cells
Affinity Maturation
- Antibody affinity increases due to exposure to prolonged or repeated protein antigen stimulation.
- This occurs in germinal centers of lymphoid follicles
- Somatic mutations in Ig V genes lead to the selection of high-affinity B cells.
Memory Cells
- High-affinity isotype-switched B cells; do not secrete antibodies but circulate in blood.
- They reside in mucosal and other tissues.
- They survive for months or years and respond quickly to reintroduced antigens.
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Description
Explore the intricacies of the humoral immune response, focusing on the roles of antibodies and the maturation of B lymphocytes. This quiz covers antibody types, their functions, and the phases of B lymphocyte activation. Understand how these immune cells interact with antigens to provide defense against pathogens.
