B cell development / differentiation upon activation (Exam III) Flashcards
B cell development / differentiation
T cell dependent interactions
What phases of B cell development are in the BM?
Repertoire assembly
Negative selection
What phases of B cell development are in the secondary lymphoid organs and circulation?
Positive selection
Searching for infection
Finding infections
Attacking infection
List the B cell development order
Repertoire assembly
Negative Selection
Positive selection
Searching for infection
Finding Infection
Attacking infection
Repertoire assembly
Generation of clonally expressed B cell receptors in the bone marrow
Negative selection
Alteration, elimination or inactivation of B cells receptors that bind to components of the human body
positive selection
promotion of a fraction of immature B cells to become mature B cells in the secondary lymphoid tissues
searching for infection
recirculation of mature B cells between lymph, blood, and secondary lymphoid tissues
finding infection
Activation and clonal expansion of B cells by pathogen derived antigens in secondary lymphoid tissues
attacking infection
Differentiation to antibody-secreting plasma cells and memory B cells in secondary lymphoid tissue
Pro B cell stages
- Early Pro B cell
- Heavy chain rearrangement
Pre B cell stages
- Check point
- Light chain rearrangement
- Second checkpoint
Immature B cell phase
- Immature B cell
Early pro B cell
commits to B cell lineage
Heavy chain rearrangement
Generates heavy chain gene diversity in pro-B cell population
First checkpoint (development of B cell)
Selects for functional heavy chains
Light chain rearrangement
Generates light chain gene diversity in pre- cell population
Second checkpoint (B cell development)
Selects for functional light chains
Immature B cell stage
Makes functional IgM
Pre-B cell receptor testing, would be considered to be in what phase of B cell activation?
First checkpoint
Second checkpoint
functional rearrangement of light chains
what which point is BTK required?
first checkpoint - testing of Pre - B cell receptor
Pre B cell receptor (intracellular expression)
- Signals from a properly assembled Pre B cell receptor, induces allelic exclusion at other heavy chain locus
- surrgoate light chain takes place of rearranged light chain
- allows for testing of the heavy chain
surrogate light chain composition (PRE-B cell receptor
- VpreB
- Labmbda 5
B cell receptor surface expression
Fully formed B cell receptor has both heavy and light chains
early pro B cell survival
H - chain rearrangement
- D-J rearrangement on both chromocomes
(if positive, moves on to late pro B cell phase)
Late pro B cell
Heavy chain rearrangement
- V-DJ rearrangement on first chromosome (if positive, signaled to survive and become Pre B cell)
- if ^ didn’t work, V-DJ rearrangement on second chromsome (if positive, signaled to survive and become Pre B cell)
- If neither worked, signaled to die by apoptosis: 50% of cells
Pre B cell light chain rearrangement order
- Rearrange K on first chromosome
- Rearrange K on second chromosome
- Rearrange Lambda on first chromosome
- Rearrange Lambda on second chromosome
If any of these worked, cell becomes immature B cells. If not - Apoptosis
As many as _ successive attempts can be made at successful rearrangement of the _ chain
5; kappa
between its V-J
Immature B cell selection:
Immature B cell undergoes Negative selection.
**Still bone marrow **
Receptor editing allows the immature B cell more chances to make a non-autoreactive BCR (editing only in light chain)
Immature B cell continues to rearrange light chain genes
**Immature B cell makes a new light chain and thus an IgM with a different specificity **
- if the new receptor is NOT self-reactive, the B cell leaves the bone marrow.
1. this cell moves into the blood and expresses IgM and IgD, and can search for antigens for activation.
- if the new receptor is self reative, light chain genes continue rearranging.
1. successive new receptors are self reactive. no further rearrangement are possible and the immature B cell undergoes apoptosis
Maturation of B cells
- Immature B cells leave the bone marrow and enter circulation, secondary lymphoid organs, and lymph
- to survive and mature, immature *B cells must enter lymphoid follicles *
- Interaction with Follicular dendritic cells (FD) provides the required maturation and survival signals - positive selection
- competition with other B cells is the limiting factor for space in the follicle
B cell interaction with Follicular dendritic cells
provides the required maturation and survival signals - positive selection.
B cell precursors rearrange its immunoglobin genes
Generation of B cells receptors in the bone marrow
immature B cell bound to self cell surface antigen is removed from the repertoire
negative selection in the bone marrow
mature B cell bound to foreign antigen is activated
migration of B cells to peripheral lymphoid organs and activation (for positive selection)
Activated B cells give rise to plasma cells and memory cells
antibody secretion and memory cells in bone marrow and lymphoid tissue
Plasma cell - IgM
antibody secretion
IgG Expressing B cell
Isotype switching
High affinity Ig-Expressing B cell
Affinity Maturation
+
Memory B cell
from naive to activated to differentitated
- Antigen recognition
- naive (IgM, IgD) B cell + antigen - Helpter T cells, other stimuli
- Activated B cells - B cell and proliferation and differentiation
**- proliferation - antibody secretion
- isotype switching (AID)
- affinity maturation (AID)
- memory B cell
Memory B cell vs B plasma cell
Plasma cell - secretes antibodies off the surface
memory cell - antibody remains on the surface of the cell
how does antigen get noticed by B cells
- Antigen arrives from tissues via affarent lymphatics into lymphoid organs (follicle)
1. small antigens delivered to follicles via conduits - May be picked up by (conventional) denritic cells in medulla and migrate to lymphoid organs (follicle)
- Larger antigen taken up by macrophages in subscapular sinus and denritic cells in medulla and travel to follicle
follicular dendritic cells display
intact antigens on their cell surface so that B cells receptors can bind to them and become activated
enigmatic dendritic cells
storage vessels for antigens.
Ready for B cell stimulation.
follicular dendritic cells express:
2 types of different complement receptors that bind to intact antigens or pathogens that are coated with complement opsinins.
- CR1
- CR2
two types of antigens activate B cells
- T dependent antigens - Require T cell help for production of antibodies
- T independent antigens - no requirement for T cell help
antigen binding site of the BCR
consists of the heavy and light chain in the variable region
BCR signaling requires the assistance of
the signaling machine IgA+IgB
B cells become activated when their receptors are cross linked by antigens
antigen binding site binds with high affinity to a given antigen. if that antigen is repeated on the surface of the bacteria/pathogen, then the erceptors of the B cells may express cross linkage.
Cross linkage - the receptors are brought together, so that the signal can be amplified by the fact that many B cell receptors are being triggered at the same time.
Clustering of antigen receptors allows receptor associated kinases to phosphorylate the ITAMS
Syk binds to doubly phospjorylated ITAMs and is activated on binding
Much like T cell activation, B cell activation requires cross linking (clustering) and association with signaling with signaling adapters
The signaling cascade is initiated from the ITAM domains in IgA, and IgB
b cell receptors perform crosslinkage through antigens which leads to
change in gene expression in nucleus
BTK
necessary for activation of the signaling cascade
downstream of the signaling cascade, these trancsription factors are activated
- NFAT
- NFkB
- AP-1
move to the nucleus where they initiate changes in gene expressions
the signaling thorugh of BCR through IgA and IgA requires
BTK
BCR triggering is greatly enhanced by
- B cell co-receptor
- CD40/CD40 ligand
B cell co-receptor
- CDR19/CR2/CD81 (complex)
- increase BCR signal by up to 10,000 fold
- work best with complement labeled antigens bringing together complement receptors and BCR
CD40/CD40 lignad
Interaction with T cells
- essential for T cell help
- required for isotype switching and affinity maturation
B- Cell complex (CR2, CD19, CD81)
if an antigen is bound by complement, it will bind to CR2 and then reqruit the rest of the complex to enhance signaling
B cell activation
Any complement labeled item (pathogen or protein) can bind to B cell receptor
CD40: CD40L
B cells need two signals for full activation by T dependent antigens
???????
B cell receptor binds an antigen. leads to signal 1 indicating B cell receotri had bound annd recognized the antigen its specific for.
Taken up bymediated endocytosis. antigen presented as MHCII
T dependent antigens
require T cell help for production of antibodies
- typically protein antigens
T independent antigens
TI - 1
- a combination of BCR and TLR signals activate B cell
TI-2
- Repetitive carbohydrate antigens present at high density on a pathogen surface, leads to extensive BCR cross linking
TI - antigens require contribution from TLR signaling
- B cell receptor
- TLR4
TI- 2 antigens
All about cross-linking
High density on pathogen surface
- recruit B cell receptors together
- Many repeated antigens close together
what antibody isotype can be generated from T independent reactions?
IgM only
Differentation of activated B cells in secondayr lymphoid organs
- upon antigen encounter in lymphoid organs, B cells are detained in the T cel areas where they recieve signals to proliferate and differentiate
- some become plasma cells and migrate to medullary cords or to the bone marrow
- plasma cells have no cell surface immunoglobin or MHC class II, no furhter division, specialized for antibody secretion
plasma cells are devoted to
antibody production
Germinal centers
- Other activated B cells migrate to a nearby follicle which becomes a secondary follicle, containing a germinal center
- these sites, are where somatic hypermutation, affinity maturation and isotype switching occurs
- memory B cells are maintained and circulate through the body, ready to rapidly respond upon re-exposure to pathogen.
true / false
Plasma cells undergo affinity maturation?
False
B cells are prolferating and getting T cell help in this location
Germinal center.
- activation of B cells and migration into germinal center
- B cell proliferation
- Somatic mutation and affinity maturation; isotype switchong
- exit of high affinity antibody secreting cells and B cells
Somatic hypermutation
AID makes point mutations in the variable region, leading to high affinity binding to the antigen