Questions and Answers
Which types of antigens can B cells recognize?
What process describes the generation of antibodies with increasing affinity due to repeated exposure to an antigen?
What is the difference between T-dependent and T-independent antibody responses?
What is the function of complement proteins in B cell activation?
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What characterizes the primary immune response in humoral immunity?
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What is the result of clonal expansion during the humoral immune response?
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How do naïve B lymphocytes initially recognize antigens?
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What occurs during heavy chain class switching?
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What is the role of CD40L in B cell activation?
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Which antibody isotypes are expressed by B cells before class switching occurs?
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What type of CMI is primarily involved in the elimination of helminthic infections?
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What stimulates the production of IgE during a helminthic infection?
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What is the primary function of opsonizing antibodies like IgG?
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Which type of antigens cannot be recognized by CD4+ helper T cells?
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What directs class switching in activated B cells?
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What characterizes affinity maturation in antibody responses?
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What enhances the antigen-dependent activation of B cells?
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Which type of antigens can stimulate a strong response in B cells due to their ability to cross-link antigen receptors?
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What is the role of CD40 and B7 in B cell activation?
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Which process occurs when antigens bound by B cell receptors are internalized?
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How do helper T cells stimulate B cell proliferation?
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What happens to soluble protein antigens when presented to B cells?
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What is the consequence of engaging both Ig receptors and C3b on B cells?
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Which of the following describes the fate of antigen after being processed by B lymphocytes?
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Study Notes
Humoral Immune Responses
- Humoral immunity targets extracellular microbes and toxins through B cell activation.
- B cells recognize various antigens: polysaccharides, lipids, proteins, and nucleic acids.
Phases of Humoral Immune Response
- Naïve B lymphocytes express two types of membrane-bound immunoglobulins (Ig).
- Activation leads to clonal expansion, differentiation into plasma cells, and formation of memory cells.
- Secreted antibodies maintain the same specificity as the B cell receptor.
- Heavy chain class switching allows B cells to produce different antibody classes.
- Affinity maturation occurs with repeated exposure to protein antigens, resulting in higher affinity antibodies.
Types of Antibody Response
- Antibody responses can be:
- T-dependent (primarily against protein antigens).
- T-independent (against non-protein antigens, requiring less class switching).
- Primary immune response occurs after first antigen exposure; secondary response is triggered by subsequent exposures.
B Cell Activation Process
- Initiated by B cells recognizing antigens via membrane-bound Ig receptors (first signal).
- Second signal comes from interactions with complement proteins, particularly C3b binding to CR2 (CD21).
- Both signals enhance antigen-dependent B cell activation, leading to:
- Cell cycle entry and clone expansion.
- Production of IgM and preparation for interaction with T helper cells.
Role of Complement Proteins
- Complement proteins, specifically C3b, enhance B cell activation through increased antigen recognition.
Interaction with Helper T Cells
- B cells prepare for T cell interaction by expressing CD40 and B7, providing necessary co-stimulatory signals.
- Helper T cells stimulate B cell proliferation and differentiation in lymphoid organs.
Antigen Processing by B Lymphocytes
- Antigen internalized by BCR undergoes endocytosis, processed into peptides, and displayed via class II MHC to helper T cells.
Mechanism of Helper T Cell-Mediated Activation
- CD40L on activated T cells binds to CD40 on B cells, resulting in:
- Clonal expansion.
- Antibody production.
- Increased T cell cytokine receptor expression.
- Heavy chain class switching and affinity maturation.
Heavy Chain Class Switching
- Activated B cells initially express IgM and IgD; class switching allows for the production of IgG and IgE.
- IgG subclasses (IgG1 & IgG3) are optimal for opsonization due to high-affinity Fc receptors on phagocytes.
- Class switching is cytokine-directed and initiated by CD40L signals.
- IFN-γ from TH1 cells promotes switching to IgG, while IL-4 from TH2 cells promotes switching to IgE for helminthic infections.
Affinity Maturation
- Ongoing process during T-dependent responses increases the affinity of antibodies for specific antigens.
Responses to T-Independent Antigens
- T-independent (TI) antigens, such as polysaccharides and glycolipids, do not utilize CD4+ T helper cells for recognition.
- Most TI antigens are multivalent, possessing repeated identical epitopes, promoting B cell activation independently.
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Description
This quiz explores the key concepts of humoral immune responses, including the role of B cells in recognizing and responding to various antigens. It covers the phases of the humoral immune response and the types of antigens, such as proteins and lipids. Test your understanding of how humoral immunity neutralizes extracellular microbes and toxins.
