B Cell activation and development (Bowden) Flashcards
Where are the checkpoints in B cell maturation
Pre-B cell stage checking 3D arrangement of R
After replacing surrogate light chains
Then negative selection
positive selection
What markers do we use to detect B cells
CD19+ and CD20+
How do mature B cells enter tissue
HEV
What do resting mature B cells express
BCell R co-B cell R (CD19, CD81, CR2,) all make CD21 HLA-DR (class II) CD40 CD45 CD20
B cells that develop from fetal liver-derived stem cells differentiate into what
B-1 cells. respond to non-protein Ag in the mucosa (CD5+) GALT and MALT etc
B cells that develop from BM progenitors after both differentiate into what
B2 cells
Major subsets of B-2 cells
follicular B cells- majority (re-circulating)
Marginal B cells- in spleen and are blood-borne polysaccharide Ags
Antigen dependent overview steps
Initiated by Ag(epitope) recognized by B cell R (Idiotope)
Ag binds mIg on naive cells to activate
T dependent or independent manner
Where are naive B cells found
secondary lymphoid tissues: primary lymphoid follicles, spleen, and lymph nodes
What cells are found in primary lymphoid follicles
Follicular dendritic Cells- not APCs not hematopoietic
Describe the passage through secondary lymphoid tissues
enter thru HEV, no antigen yet. migrate to primary follicle, receive signal to survive from FDCs and exit thru lymphatic vessel
What is the bodies mechanism for maintaining concentration of B cells
too many B cells, not enough FDCs to provide survival signals
naive B cells die within weeks in absence of antigen
How are B cells “attracted or homing” to tissue location
express L-selectin, CCR7, LFA-1 and CXCR4
these bind PNAD, CXCL19, ICAM-1 and CXCR12
chemokine binding activates integrins and follicle migration is mediated by CXCL13
How many signals does B cell activation need
2
first signal of B cell activation
Ag recognized by mIgM or D- must cross link 2 or more BCR
signal thru Igalpha and beta tails
What is the other version of the first signal for B cell activation
Ag binds C3d which is recognized by mIg and CR2(provides the cross linking)
signal thru Ig alpha and beta tails as well as CR2 and CD19 tails
How does lymphocyte migrate after 1st signal of B cell activation
B cells down reg CXCR5 and upreg CCR7
T cells down reg CCR7 and upreg CXCR5
What is stimulated when Ag bings the epitope(Ab) in B cell activation
degraded, then presented on MHC which when in contact with TCR stimulates B7 expression on B cell
What is the second signal of B cell activation
Cd40 on B cell interacts with CD40L on T cell
How come CD40L and B7 expression are dependent on antigen stimulation?
only lymphocytes interacting with the antigen will be activated= specificity
2 general functions of cytokines released by Thelper cells
induce H chain class switching augment B cell differentiation and proliferation(clonal expansion)
Explain the effects of Th cytokines on H chain class switching
IL4 promotes IgE
IFNgamma induces IgG2a
TGF-beta and IL5 lead to IgA
What is required for HLA isoptope switching? How does this happen?
CD40-CD40L so T dependent Ag (proteins only)
Using downstream Constant region(cut out intervening sequences) dependent on cytokines
Key enzyme in the HLA isotope switching
activation-induced deaminase AID
expressed by CD40
What does a naive B cell DNA look like
activated VDJ and Cmu and Cdelta, still have all other downstream constant regions
Naive cell +LPS DNA
LPS is t independent no other constant regions are activated aka no class switching
Naive cell + LPS and IL4 and soluble CD40L DNA
switch area is at IgGgamma and IgE epsilom
Naive cell +LPS and TGF-beta DNA
IgGgamma2b and Igalpha
Class switching depends on how many cytokines
all- predominant one wins
Somatic hypermutation/affinity maturation
Cs–>Us point mutations by AID enzyme in variable region.
expansion or répertoire
want more high affinity Ag specific Ab
T antigen dependent
During what stage do Ab increase affinity
somatic hypermutation, in germinal centers because interacting with FDC
How do mutations change over primary-tertiary response
changes start to accumulate at end of primary response, then much more at secondary and tertiary.
Plasma cells
terminally differentiated B cells.
how do we identify plasma cells
CD29 secrete super amounts of Ab
Memory B cells
long periods of time without additional Ag stimulation. Rapid response for future exposure
T independent antigens
do not require T helper cells. these are mitogens
T dependent antigens
require T helper cells- contact dependent
Do T independent antigen immune responses provide memory cells
no
What happens in a T dependent Ag response compared to an independent
T dependent Ag: have isotope switching, affinity maturation and immunologic memory while TI antigens do not
Describe Ab feedback
secreted Ab has neg feedback. IgGonly
through Igalpha and beta tails
Natural antibodies
IgM- produced by B-1 and marginal zone B cells
Specific for local bacteria (limited repertoire)
cross-react with alloantigens
What increases when antigen binds naive B cell
survival and proliferation
expression of B7
expression of cytokine R like IL2 and IL4 R
expression of CCR7 and migration from follicle to T cell areas
When T cells interact with B cell what cascades follow
Ab secretion, Isotope switching, affinity maturation and memory B cell production
What are the two groups of T-independent antigens and describe
TI-1 act as polyclonal stimulators
TI-2 are polymers that activate by cross linking the BCR
Most important co stimulatory molecule on B cells
CD40- lowers threshold of Ag needed
Does class switching the Ig change the specificity of the Ab
no, only its isotope– function
