B cell maturation Flashcards
what kind of receptor do B cells express
B cell receptor (BCR)
how does BCR recognize antigen
via membrane Ig
T/F the BCR on each B cell clone is specific for a distinct antigen
True
what are the five Ig types
IgG, IgE, IgM, IgA, IgD
Ig isotype is based on what
heavy chain
which Ig(‘s) is/are monomeric with 2 binding sites
IgD, IgE, IgG
which Ig(‘s) is/are pentamers with 10 binding sites
IgM
which Ig(‘s) is/are dimers with 4 binding sites
IgA
Ig are Y shaped molecules formed by:
two heavy chains and two light chains
what does the light chain consist of
1 variable domain and 1 constant domain
what does the heavy chain consist of
1 variable domain and 3 or 4 constant domains
what are the two forms that Ig can exist in
membrane-bound or secreted
which region contains the antigen binding site
variable regions
which region mediates the effector function? and what are those funcitons?
constant region.
- determines isotype
- bind complement
- bind Fc receptors
how many bind sites are there per Y structue
2
does variable chain bind wide variety of antigen or a very specific type of antigen
wide variety (in contrast with T cells):
- proteins
- lipids
- polysaccharides
- nucleic acid
does variable chain recognize processed or non-processed antigen
native not processed antigen is recognized
(in contrast with T cell receptor which recognizes processed peptide)
what is the antigen part recognized by antibody
epitope
which is the first C region cluster
Cu (greek letter mu)
which is the first antibody to be produced
IgM
during recombination of Ig genes, is it randomly selected or precisely selected?
random
what is the random recombination mediated by
RAG specific for VDJ
- brings two segments close together
how else is diversity generated for Ig
exonucleases and Tdt
where does B cell positive selection occur
bone marrow
is positive selection for B cells antigen dependent or independent
antigen independent
what are the two checkpoints in B cell maturation
preBCR and IgM
T/F B cell needs either preBCR or IgM to promote survival
False. It needs both preBCR and IgM
what is negative selection for B cells
eliminate B cells that can bind with high affinity ubiquitous self antigens
what else can a B cell do instead of dying that results in change of the Ig specificity
Receptor editing
what do plasma cells produce
high affinity Ig
where do plasma cells migrate to and how long do they survive
Bone marrow or mucosal tissues
survive for years
do memory B cells secrete Ig
nope
how long do memory B cells survive and where
a lifetime in mucosal tissues and blood
compare secondary antibody response to primary antibody response in terms of
1. response time
2. response amount
3. antibody type
4. antibody affinity
Primary: slower, smaller, IgM > IgG, low affinity
Secondary: quicker, larger, IgG more abundant, high affinity
what are two to enhance B cell activation
- simultaneous engagement of antigen receptor (BCR) and CR2
- TLR
what delivers the CR2 activating signal
CD19 and CD81
what are the two types of antibody responses
T dependent response and T independent response
for the T dependent response, what kind of antigen, what Ig, and what kind of affinity?
- protein antigen (T cells only recognize protein antigens)
- isotype switching
- high affinity Ig
for the T independent response, what kind of antigen, what Ig, and what kind of affinity?
- nonprotein antigen
- IgM
- low affinity Ig
define a hapten
small molecule that cannot elicit an immune response by themselves but do so after bind to larger proteins or cells
what are the steps of T-B cell interaction and antibody responses?
- simultaneous activation of T and B cells by antigen in T cell zone and follicle, respectively
- migration towards each other
- B cells migrate back to follicles where germinal center rnx occurs
which chemokine is for T cells to go to T cell zone
CCR7
which chemokine is for B cells to go to B cell zone (follicle)
CXCR5
during antigen presentation by B cells to T helper cells, which cell processes the antigen
B cells
T/F B cells and T cells recognize different epitopes of the same protein
True
which protein epitope do B cells recognize
native conformational epitope
which protein epitope do T cells recognize
peptide fragments
when T cell recognizes peptide presented to it by the B cell, what does this induce
CD40L upregulation in T cells and production of cytokines
in the B and T cell interaction, where is CD40 present and where is CD40L present?
CD40 on B cells
CD40L on T cells
what does engagement of CD40 and cytokine receptor on B cells lead to
proliferation and differentiation in plasma cells
what 3 things happen in the germinal center
isotype switching
affinity maturation
selection of high-affinity B cells
what is isotype switching
change in the C region of the heavy chain with no change in specificity (recognition of antigen doesn’t change)
what does isotype switching require
CD40L signal from Tfh (T follicular helper cells)
the type of heavy chain isotype is determined by what
cytokines produced by Tfh cells (IgG and IgE) or tissues (IgA)
what happens during switch recombination
the VDJ exon is brought next to a different C gene
T/F during switch recombination the specificity of the Ig does not change, while the C region is different and reflected the function of the Ig
True
what is affinity maturation
point mutation in the V regions
- selection of B cells with high-affinity antigen receptors
during selection of high-affinity B cells, what interactions promote their survival
interactions with follicular DC that display antigen and Tfh cells
T/F B cells compete for antigen and those with low affinity for antigen will survive
False. those with high affinity will survive
