B cells 2 ppt
Page 1: Introduction to B Cells
Title: Overview of B cells
Contact: Emily Gwyer Findlay - e.gwyerfindlay@soton.ac.uk
Page 2: Lecture Overview
Key Topics Covered:
Overview of B cells
Structure and diversity of B cell receptors and antibodies
B cell development and activation
Antibody subclasses and their functions
Plasma cells and memory cells
Page 3: B Cell Recombination
Heavy Chain Recombination:
Crucial for B cell development
Light Chain Recombination:
Follows heavy chain recombination
Key Terms:
BONE MARROW, STROMAL CELL, IL-7, KIT, PRE BCR, ANTIGEN-DEPENDENT, IMMATURE B CELL
Maturation Process:
Progenitor B cells develop in the bone marrow.
Page 4: Function of B Cells
Antibody Production:
B cells release antibodies responsive to specific antigens.
Model suggests production of up to one quintillion unique antibodies.
Production depends on the specific antigen exposure each B cell experiences.
Page 5: B Cell Activation and Proliferation
Antibody Selection:
Processes include Affinity selection, CSR (Class Switch Recombination).
B Cell Types:
Plasma Cells: Short-lived, produce IgM.
Memory B Cells: Long-lived, retain memory for future responses.
Page 6: T Cell Help and Activation
Activation Mechanisms:
Thymus-Dependent: Requires T helper cells for B cell activation.
Thymus-Independent: Activation occurs without T helper involvement.
Page 7: Thymus-Independent Antigens
Characteristics:
Typically polysaccharides with repeating sugar sequences.
Stimulate B cell activation via surface IgM and IgD binding.
Release mainly IgM antibodies.
Page 8: Antigen-Dependent Maturation
Requirement for T Cell Help:
Process known as Linked Recognition
T cell assistance is vital for full B cell activation and maturation.
Page 9: The Role of T Helper Cells
Interaction Steps:
BCR Binding: BCR binds to antigen.
Antigen Presentation: Antigen internalized and presented via MHC class II.
TCR Recognition: T cells recognize MHC/antigen complex.
Cytokine Release: T cells stimulate B cells to produce antibodies.
Page 10: Cytokine Signaling
Key Cytokines in B Cell Activation:
IL-4: Drives B cell proliferation.
IL-5 & IL-6: Stimulate plasma cell development.
Page 11: Germinal Center Reaction
Germinal Center Functionality:
Site for B cell proliferation and differentiation.
Includes processes of somatic hypermutation, affinity maturation, and class switching.
Page 12: Somatic Hypermutation
Processes Involved:
Introduces point mutations in the V region.
Enhances antigen binding affinity through natural selection of B cells with improved receptors.
Page 13: Mechanism of Somatic Hypermutation
Molecular Mechanism:
AID (Activation-Induced Cytidine Deaminase): Facilitates mutations and receptor refinement.
Page 14: Affinity Maturation
Selection Process:
Continual refinement of antibody affinity through selection of improved antigen binders.
Page 15: Vaccination Impact
Higher Affinity Antibodies:
Vaccination enhances production of high-affinity antibodies against specific pathogens.
Page 16: Class Switching
Mechanism of Class Switching:
Occurs through DNA recombination following T cell help.
Produces IgG, IgA, or IgE antibodies, changing effector functions.
Page 17: Mechanism of Class Switching
Functionality Remains:
Variable region (VDJ) unchanged but constant region altered to modify antibody function.
Page 18: Diversity Generation
Antigen-Independent vs. Dependent Mechanisms:
Independent: Involves pairing of heavy/light chains and junctional diversity.
Dependent: Involves somatic hypermutation, class switching, and affinity maturation in response to antigen exposure.
Page 19: Functions of Antibodies
Class Functions:
Neutralization: Inactivates toxins and viruses.
Opsonization: Marks pathogens for phagocytosis by immune cells.
Complement Activation: Enhances immune response.
Page 20: Fc Receptors
Characteristics:
Bind specifically to the Fc region of antibodies.
Distributed across various immune cell types including NK cells and macrophages.
Page 21: Roles of Fc Receptors
Functions:
Enable phagocytosis through antibody binding.
Facilitate ADCC (Antibody-dependent cell-mediated cytotoxicity) by NK cells.
Page 22: Cytokine Production by B Cells
Production Rate:
Slower than T cells; not a critical feature.
Role in T Cell Migration:
B cells secrete chemokines to recruit T cells, regulating immune responses.
Page 23: Antibody Subclasses
Types of Antibodies:
IgM: First antibody produced;
IgD: Surface receptor, expressed on activation;
IgG: Most abundant, crosses placenta;
IgA: Found in mucosal areas;
IgE: Associated with allergic responses.
Page 24: IgM & IgD Features
IgM: Pentameric structure with high avidity.
IgD: Not secreted, involved in B cell signaling.
Page 25: Role of IgG
Characteristics:
Most prevalent in sera; critical for placental immunity and cellular responses.
Subclasses: Different IgG subclasses have varied roles in immunity.
Page 26: IgA & IgE Functions
IgA: Primarily at mucosal surfaces; vital for gut defense.
IgE: Least common; primarily involved in allergy and parasite defense.
Page 27: Summary of Antibody Functions
Functional Activities:
Various Ig isotypes involved in neutralization, opsonization, and attack pathways against pathogens.
Page 28: Implications of CD40L Deletion
Effects on Antibody Production:
Lack of class switching affects the antibody profile.
Page 29: Memory B Cells
Differentiation Process:
Controlled by BLIMP1; memory B cells have high specificity for pathogens.
Page 30: Plasma Cells
Production Capacity:
Can produce 2000 antibodies/second but have a short lifespan.
Page 31: Memory B Cells in Response
Response Characteristics:
Rapid and higher affinity production of antibodies upon antigen re-exposure.
Page 32: Immune Response Dynamics
Primary vs. Secondary Response:
Distinct differences in antibody concentration and classes produced during infection phases.
Page 33: Dysregulated B Cell Responses
Systemic Lupus Erythematosus (SLE):
Condition where B cells produce antibodies against self-antigens due to survival of self-reactive B cells.
Page 34: SLE Statistics
Demographics & Impact:
Predominantly affects women; causes significant health issues including renal complications.
Page 35: Summary of B Cell Development
B Cell Receptor Structure:
Made of heavy and light chains; VDJ recombination leads to diversity.
Page 36: Summary of Key B Cell Processes
Key Processes:
Antigen presentation to T cells, engagement in somatic hypermutation and affinity maturation, resultant antibody functions in immune responses.