B-IV B-cell function Flashcards
What is required for signaling into the nucleus of a B-cell?
Invariant chain ( consisting of Ig alpha, and beta)
Signaling is crucial for B-cell development and function.
What is the first step in B-cell development during the antigen-independent phase?
Heavy chain locus rearrangement
This occurs in the pro-B cell stage in the bone marrow.
What do pre-B cells express to check if the receptor works?
Surrogate light chain
The pre-B cell receptor includes a μ chain as an invariant surrogate chain.
What is the most common light chain in BCR?
κ chain
The light chain rearrangement is driven by the pre-BCR signaling.
What happens to a naive B-cell upon antigen stimulation?
Activation
This leads to differentiation into plasma cells.
What occurs during the antigen-dependent phase of B-cell development?
Activation and differentiation
If no antibodies bind, the cell undergoes apoptosis.
What is allelic exclusion in B-cell development?
Only one allele is expressed. The other is inhibited by a functional gene product
A productive locus inhibits the other allele to ensure a single functional receptor.
What are the two types of selection in B-cell development?
Positive and negative selection
These processes ensure B-cell tolerance and prevent autoimmunity.
What is the role of the germinal center in B-cell activation?
Formation of antibody-producing cells and affinity maturation
Activated T and B-cells interact here, leading to higher affinity antibodies.
What cytokines are involved in class switching of B-cells?
IFN-γ, IL-4, IL-5, TGF-β, IL-21
These cytokines help produce different antibody classes beyond IgM.
What is the function of plasma cells?
High Ig secretion, low/no BCR expression
Plasma cells are fully differentiated and do not proliferate in response to antigens.
What is the function of the FcγRIIB receptor on B-cells?
Inhibits BCR signaling
This downregulates immune responses.
What types of antigens require T-cell help for B-cell activation?
Thymus dependent antigens (TD Ag)
These include proteins and lead to memory cell formation.
What is the difference between thymus independent antigens (TI Ag) and thymus dependent antigens?
TI Ag do not require T-cell help and mainly induce IgM production
They do not undergo isotype switching or affinity maturation.
What is the hapten-carrier effect?
B-cell processes carrier protein and presents peptide to T-cell, enabling T-cell to activate the B-cell and recognize a different epitope than the B-cell
This enables the T-cell to activate the B-cell, recognizing different epitopes.
What is the unique marker for the B-1 subset of B-cells?
CD5
B-1 cells primarily produce IgM and are found in mucosal sites.
What are the functions of antibodies?
Neutralization, opsonization, cellular cytotoxicity, mast cell activation, complement activation
Each function is associated with specific antibody classes.
What is the difference between polyclonal and monoclonal antibodies?
Polyclonal: several B-cell clones; Monoclonal: one B-cell clone
Monoclonal antibodies are produced using hybridoma technology.
What happens to naive B-cells when there is no antigen present in the lymph node?
They undergo apoptosis
This process ensures that only activated B-cells persist.
What role does activation-induced deaminase (AID) play in B-cell function?
Causes somatic mutations in CDR regions
This enhances the affinity of antibodies produced.
What do bone-marrow stromal cells do?
Bind to pro-B-cells, secrete IL-7 which causes proliferation and development into pre-B-cells
What is the different between pro-B-cells and pre-B-cells?
pre-B-cells expresses pre-B receptor at surface; H-chain genes are rearrenged
What is the function of the pre-BCR
To test if the heavy chain is functional, and signal to the light chain locus to begin rearrangement if so
Which is the more common light chain?
Kappa
What is the difference between a immature and a naive B-cell?
An immature B cell expresses only IgM as a surface Ig, while a naive B cell expresses both IgM and IgD
What does negative selection mean?
If the BCR react strongly, it means it react towards self-antigens. This causes apoptosis of those B-cells
What does positive selection mean?
If they have weak self-antigen recognition, these are selected for proliferation
Which chemokine receptor causes movement towards the follicle?
CCR5
Which chemokine receptor causes movement towards the paracortex?
CCR7
How do the chemokine receptors change in the T and B-cells after activation?
T-cells: Less CCR7 and more CCR5
B-cells: More CCR7 and less CCR5
Using which receptor(s) do the T and B-cell communicate?
MHC Class II expressed on the B cell. CD40 receptor on B cell and CD40 ligand on T-cell, and cytokines secreted from T-cell
What causes affinity maturation?
Binding of the CD40R and CD40L
What is the function of follicular dendritic cells?
Presenting the antigen to mutated B-cells. After hypermutation of the CDR in the BCR, the B-cells can test the binding of the BCR to the antigen in question and see if the affinity is higher or lower. If higher, they go into differentiation
What causes isotype switching?
Cytokines secreted from T-cells
Which cytokine induces IgG (subclasses)?
IFN-γ, IL-21
Which cytokine induces IgE?
IL-4
What are the important activation markers for B-cells?
B7 - needed for T-cell to recognize them. Only expressed after activation
How does Fc-gamma-RIIB dampen the immune response?
Inhibits the signaling of BCR by dephosphorylation of the tyrosine residues
What is a thymus-dependent antigen?
An antigen for which the B-cell needs to be activated with a T-cell help. Here we have the isotype switching, affinity maturation, memory cells
What is a thymus-independent antigen?
T-cells cannot respond to these, so we only have a B-cell response. Only IgM
When is the B-1 subset of B-cells produced
Before birth in the fetal liver
