7. B cells II Flashcards
(21 cards)
Where do B cells initially develop?
Bone marrow
What are the possible developmental paths for mature B cells upon activation?
- Become short-lived plasma cells producing IgM
- Enter germinal centers for further development
- Undergo class switching to produce different antibody isotypes
- Develop into memory B cells for long-term protection
Define Thymus-Independent Antigens.
- Typically polysaccharides with repeating sugar units
- Activate B cells without T cell help
- Lead primarily to IgM production
- Cannot induce memory or efficient class switching
What is the role of T cells in Thymus-Dependent Antigens?
- Require T cell help for full B cell activation
- Involves linked recognition of the same antigen by both T and B cells
- T cells provide help through CD40L-CD40 interaction and cytokines
What occurs in germinal centers?
- Somatic hypermutation
- Affinity maturation
- Class switching
When do germinal centers form in lymph nodes after infection?
7-10 days
What is Somatic Hypermutation?
- Mutation rate in variable regions is 1 million times higher than normal cells
- Targets complementarity-determining regions (CDRs)
- Mediated by enzyme AID
- Introduces point mutations in variable regions of heavy and light chains
What is Affinity Maturation?
- Selection of B cells with mutations that increase antigen binding
- Higher-affinity B cells receive stronger survival signals
- Lower-affinity B cells undergo apoptosis
What is Class Switching?
- Changes antibody isotype without altering antigen specificity
- Requires T cell help via CD40-CD40L interaction
- Allows antibodies to perform different effector functions
List the major antibody functions.
- Neutralization
- Complement activation
- Opsonization
What is the function of Fc receptors?
- Bind constant (Fc) regions of antibodies
- Trigger different responses depending on cell type
What are the main characteristics of IgM?
- First antibody produced in primary response
- Pentameric structure
- Excellent at activating complement
- Primarily found in blood
What is the primary role of IgD?
Functions as B cell receptor
What distinguishes IgG?
- Most abundant antibody in blood
- Monomeric structure
- Only antibody that crosses placenta
- Excellent at opsonization
What is the main function of IgA?
Primarily functions in neutralization
What is the role of IgE?
- Binds to Fc receptors on mast cells
- Important for parasite defense
- Mediates allergic responses
Describe plasma cells.
- Terminal differentiation state
- Specialized antibody-secreting factories
- Short-lived (days to weeks)
- Cannot undergo further somatic mutation or class switching
What are memory B cells?
- Long-lived cells
- Respond more rapidly than naive B cells
- Already class-switched (mostly IgG)
- Higher affinity than primary response B cells
What pathology can B cells cause?
Autoimmune disease when self-reactivity is not properly regulated
What is systemic lupus erythematosus (SLE)?
A classic B cell-mediated autoimmune disease
What treatment is used for SLE?
B cell depletion (rituximab)
