Questions and Answers
Where do B cells get activated?
In the periphery, where they have antibodies on their surface to bind to antigens.
How do B cells get activated?
1st signal by the antigen, 2nd signal by the T cell, 3rd signal by cytokines from the T cell.
What type of interaction with T cells is required for T cell dependent B cell activation?
Cognate interaction.
What interaction is necessary with the T cell co-stimulatory molecule?
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What are on B cell surfaces that help it become activated?
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How does the MHC molecule display an antigen to the T cell?
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T cells can ONLY see an antigen from a B cell if?
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Explain the role of T cells in B cell activation in T dependent B-cell activation.
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What activates T cells and can be found on the surface of B cells when it has been bound with an antigen?
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What is the first step in B cell activation?
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What delivers the signals of the antigen crosslinking with antibodies/BCRs?
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What are the 3 major intracellular signaling pathways ending in transcription factors that get triggered upon B cell activation?
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Describe the NF-AT ending intracellular signaling pathways triggered upon B cell activation.
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Describe the NF-KB ending intracellular signaling pathways triggered upon B cell activation.
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Describe the AP-1 ending intracellular signaling pathways triggered upon B cell activation.
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What is in the B cell coreceptor?
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How do B cell coreceptors amplify activation?
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Activation of resting B cells by T helper cells depends directly upon costimulatory interaction between?
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What is negative signaling?
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Which B cell types actually secrete antibodies?
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CD19 is usually a marker found on ALL types of B cells.
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What is special about CD81, an aspect of the B cell coreceptor?
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Describe T (independent antigen) T1 vs T2.
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Study Notes
B Cell Activation Overview
- B cells become activated in the periphery, utilizing surface antibodies to bind to specific antigens.
Activation Signals
- Initial activation requires two signals:
- First signal from the antigen binding to B cell receptors.
- Second signal from T cells, with potential cytokine assistance as a third signal.
Cognate Interaction
- A cognate interaction between B cells and T cells is essential for T cell-dependent B cell activation.
Costimulatory Molecules
- Activation interaction involves CD40L on T cells interacting with CD40 receptors on B cells.
Surface Markers and Activation
- Key components on B cell surfaces aiding activation include:
- Antibodies for antigen binding.
- MHC molecules that present antigen peptides to T cells.
- CD40 receptors which receive signals from T cell CD40L.
- Complement receptors facilitating the immune response.
MHC Function
- B cells endocytose antigens, process them, and present peptide fragments on MHC molecules for T cell recognition.
T Cell Interaction Requirement
- T cells can only recognize antigens presented by B cells through their MHC molecules.
Role of T Cells
- T cells activate B cells via MHC recognition, provide necessary signals for B cell activation, and secrete cytokines to further stimulate B cell function.
MHC Activation Post-Antigen Binding
- MHC molecules on B cells express antigenic peptides only after binding with an antigen.
Initial B Cell Activation Step
- The first step involves cross-linking of B cell receptors (BCRs) by antigens, leading to B cell activation.
Signal Transduction
- Signals from antigen cross-linking are conveyed through an Ig-alpha and Ig-beta heterodimer, activating a cascade resulting in B cell proliferation and differentiation.
Intracellular Signaling Pathways
- Major intracellular signaling pathways initiated in B cell activation include:
- NF-AT pathway.
- NF-KB pathway.
- AP-1 pathway.
NF-AT Pathway
- Involves PIP2 conversion to IP3 leading to Ca2+ and calmodulin activation, with subsequent dephosphorylation of NF-AT and its migration to the nucleus for cytokine production.
NF-KB Pathway
- Involves PIP2 to DAG and activation of PKC which phosphorylates IKB, releasing active NF-KB to enter the nucleus and promote cytokine production.
AP-1 Pathway
- Activated by Ras and Rac G proteins, leading to AP-1 transcription factor activation which enters the nucleus to stimulate cytokine expression.
B Cell Coreceptor Components
- Coreceptor includes:
- CD19
- CD21 (CR2)
- CD81 (TAPA-1)
Coreceptor Amplification
- Coreceptor binds to bacteria/antigens and delivers a strong activation signal when complement fragments interact with CR2/CD21.
T Helper Cell Interaction
- Activation of resting B cells by T helper cells relies on CD40-CD40L costimulatory interaction.
Negative Signaling Mechanism
- B cell activation needs to be regulated; Fc receptors (CD32) can inhibit signaling by phosphorylating ITIMs to downregulate Ig synthesis and B cell effectiveness.
Antibody-Secreting B Cell Type
- Plasma cells, or effector B cells, are responsible for antibody secretion.
CD19 Marker Specificity
- CD19 is generally present on all B cells except for plasma cells.
Unique Feature of CD81
- CD81 spans the transmembrane domain four times, denoting its distinctive structure among B cell coreceptor components.
T-Independent Antigens
- TI-1 antigens activate B cells via BCRs and Toll-like receptors, highlighting the complexity of B cell activation stimuli.
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Explore the key concepts of B cell activation through this comprehensive flashcard quiz. Learn about the mechanisms of activation, including the roles of T cells and cytokines in this essential immune response. Ideal for students of immunology or anyone interested in the adaptive immune system.