B Cell Immunity Flashcards
What are the three different kinds of B cells?
B1, conventional B2, marginal B3 (MZ)
What is the V-region repertoire of B1 cells?
Restricted
What are the primary locations of the three kinds of B cells
B1: body cavities (peritoneal, pleural)
B2: secondary lymphoid organs
B3: spleen
Which of the B cell populations does not need T cell help?
B1 - They respond to carbohydrate Ag, which doesn’t require T cell help
Which of the B cell populations has no memory?
B1
Which B cells are produced in the fetal liver?
B1
What is the mode of renewal of the different B cells?
B1: Self renewing
B2: replaced from bone marrow
B3: Long lived
Do B1 cells undergo somatic hypermutation or isotype switching?
No!
Where are B3 cells found?
Marginal zone of the spleen: at the junction of the white and red pulp - the interface of circulation of lymphoid tissue
Do B3 cells require T cell help?
Sometimes…
What cells are innate-like?
B1 and B3
What are most adaptive immune responses mediated by?
B2
Rank the route of immunization by immunogenic response
subcutaneous > intraperitoneal > intravenous or intragastric
what do adjuvants do?
typically delays antigen release and makes particulate immunogen readily ingestible by APCs
makes Ag particulate and large enough to stimulate a response
What dose of immunogen will result in increased immunogenicity?
Intermediate amount - both low and high doses will not give the same response
How does size affect the immunogenicity?
the larger the Ag, the more immunogenic
What are the two signals B cells require to be activated?
T-dependent:
- interaction of B cell with Ag and
- interaction of TCR with peptide/MHC complex and interaction with co-stimulatory molecules CD40 (B cell) and CD40L (T cell)
T-independent: For T-independent Ag, such as polysaccharide, the second signal can be provided by the Ag (no T cell is needed)
What do activated Th cells secrete/express to stimulate B cell proliferation?
Interaction of TCR with Ag/MHC triggers the Th cell to secrete cytokines IL4, IL5, IL6 and to express CD40L
B and T cells can recognize the same Ag. What is different about what they recognize?
They recognize the same Ag, but not the same epitope
What is different about primary vs secondary Ab response in regards to speed and Ig produced?
Primary is slow and primarily IgM
Secondary is fast and is primarily IgG
What will increase at the end of the primary response?
affinity, due to somatic hypermutation, and Ab titer
What are the major Igs of the secondary immune response?
IgG, and to a lesser extent IgE and IgA
When does isotype switching occur and what is it regulated by?
during T-dependent response, regulated by T-cell cytokines
What gene is rearranged by isotype switching
C heavy
What enzyme is required for switch recombination?
AID
What does AID recognize to mediate switch recombination?
switch sites upstream of the different Ig genes (except for delta)
What are three types of differentiation that occur in germinal centers?
isotype switching, somatic hypermutation of Ig genes, development of memory B cells/plasmablasts
What happens after an activated B cell presents Ag to a helper T cell?
somatic hypermutation in Ig V regions in rapidly proliferating germinal center B cells
What happens if a mutated B cell develops low affinity surface Ig?
It will be unable to cross link receptors and will die by apoptosis
What happens if a mutated B cell develops high affinity surface Ig?
BCR and Thelper cross linking sustain B cell maturation and proliferation, and the B cell can develop into a memory B cell or a plasmablast
What happens if a patient has an AID deficiency?
Only has IgM and the Ig genes are not somatically diversified
What is the maturation, differentiation, and isotype switching dependent upon?
Thelper cells
Discuss how Thelper cells enhance B cell function
APC presents Ag via MHCII to Thelper cell which becomes activated
The TCR then recognizes Ag/MHCII on the B cell and the Thelper secretes cytokines which stimulates proliferation and differentiation
What are the differences in Ig produced by B cells stimulated by T-independent Ag?
Ab produced is generally IgM and they are not somatically mutated, and are thus lower affinity
List some T-independent Ag
bacterial lipopolysaccharide polymerized flagellin pneumococcal polysaccharide natural polysaccharide dextrans levans hyaluronic acid
do T-independent Ags result in the formation of B memory cells?
No
