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Questions and Answers
What is the primary function of the humoral immune response?
What triggers the first signal needed for naïve B cell activation?
During clonal selection, what happens to B lymphocytes that carry receptors for self molecules?
Which immunoglobulin receptors do naive B cells commonly express?
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What is the role of activated helper T cells in B cell activation?
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What is a result of clonal selection in B lymphocytes?
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Which type of pathogens does the humoral immune response specifically target?
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What is the primary outcome after a B cell has been fully activated?
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What is the first step in B cell activation by helper T cells?
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What cytokines do activated helper T cells produce to stimulate B cells?
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Which antibody is initially secreted by activated B cells?
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What distinguishes thymus-independent antigens from thymus-dependent antigens?
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What is a significant feature of the response generated by thymus-independent antigens?
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Which factor is critical for the activation of naïve T cells by B cells?
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What is the main role of memory B cells formed after B cell activation?
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What is the nature of the antigens that typically activate B cells without T cell assistance?
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What type of antigen requires T cell help for B cell activation?
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Which type of B cell response is absent in Thymus-Independent Antigens?
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What is the main immunoglobulin produced in response to Thymus-Independent Antigens?
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What interaction is essential for immunoglobulin class switching?
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Which cytokine is known to enhance IgE production during class switching?
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What occurs during the primary immune response when encountering an antigen for the first time?
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After T cell activation, which immunoglobulin class is typically produced in high levels?
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What type of antigen typically consists of large non-peptide polymers with repeated epitopes?
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What is the main antibody produced during the primary immune response?
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How long does it typically take for antibodies to become detectable in the secondary immune response?
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What is the primary antibody produced during the secondary immune response?
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What type of B cell responds during the secondary immune response?
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What is the duration of antibody presence in the primary immune response?
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Which antibody is predominantly produced when antigens enter the body via mucosal routes?
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How does the antibody concentration in the secondary immune response compare to the primary response?
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Which immunogens typically induce the primary immune response?
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Study Notes
Humoral Immune Response
- The humoral immune response targets extracellular pathogens like bacteria and prevents the spread of intracellular pathogens.
- Antibodies produced by B lymphocytes are the key players in this response, reacting specifically to antigens that triggered their production.
Clonal Selection
- During embryonic development, a vast pool of B lymphocytes forms.
- Each naïve B lymphocyte carries a unique receptor (BCR) capable of recognizing and binding to a specific antigen.
- When an antigen enters the body, it selects the B lymphocyte with the matching receptor, binding to it and prompting proliferation.
- This leads to the creation of a clone (family) of B cells, specifically targeting that antigen.
- These selected B cells differentiate into plasma cells and secrete antibodies specific to the antigen.
- B lymphocytes that recognize self-molecules are eliminated at an early stage, preventing autoimmune reactions.
Steps of Naïve B Cell Activation
- Mature, naïve antigen-specific B cells migrate from bone marrow to peripheral lymphoid tissues like lymph nodes, where they encounter their specific antigens.
- Antigen binding to the B cell receptor (IgM and IgD) triggers the first activation signal.
- The second signal, known as the co-stimulatory signal, is provided by activated helper T cells (mainly Th2).
- To receive the second signal, the B cell engulfs the bound antigen, processes it, and presents it on its surface associated with class II MHC molecules.
- This peptide-MHC complex is recognized by antigen-specific helper T cells, leading to the release of:
- CD40L, which binds to CD40 on the B cell.
- Cytokines like IL-4, IL-5, IL-6, and IL-10, stimulating the B cell.
- Following receipt of both signals, the B cell undergoes activation, proliferates, and differentiates into effector plasma cells secreting antigen-specific antibodies.
- Initially, IgM is secreted, but the cell can switch to producing other antibody isotypes with the same antigen specificity.
- Some activated B lymphocytes become memory cells, providing a rapid response upon re-exposure to the antigen.
Thymus-Dependent and Thymus-Independent Antigens
- Thymus-Dependent (TD) Antigens:
- Require T cell help for B cell activation.
- Typically proteins, such as bacterial toxins.
- Can induce antibody class switching to IgG, IgA, and IgE.
- Generate strong memory B cell responses.
- Thymus-Independent (TI) Antigens: - Activate B cells directly without T cell cooperation. - Typically large polymers with repeating epitopes, like capsular polysaccharides. - Result in only IgM production and no class switching. - Do not generate memory B cell responses.
Immunoglobulin Class Switching (Isotype Switching)
- During an immune response, plasma cells switch from producing IgM to other immunoglobulin classes like IgG, IgA, or IgE.
- This switching involves DNA rearrangement and RNA splicing, altering the constant domains of the heavy chain (CH) without affecting the antigen specificity.
- Switching requires interaction between CD40 on B cells and CD40L on T cells.
- Cytokines released by T cells determine the antibody isotype produced.
Primary and Secondary Antibody Response
-
Primary Immune Response:
- Occurs during the initial encounter with an antigen.
- Has a lag of approximately 7-10 days for antibody production.
- Mainly produces IgM, which peaks in 1-2 weeks and rapidly declines.
-
Secondary Immune Response:
- Triggered by re-exposure to the same antigen.
- Rapid response due to memory cells generated during the primary response.
- Primarily produces IgG, with higher concentrations and longer persistence.
- Exhibits higher antibody affinity and a stronger response.
- Can be boosted by further antigen exposure.
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Description
Test your understanding of the humoral immune response, focusing on the role of B lymphocytes and antibodies. This quiz covers the concepts of clonal selection and activation of naïve B cells and their crucial function in targeting pathogens. Prepare to explore the intricate mechanisms of immune defense!
