B Cells Flashcards
Development of B cells occur in which structures
During gestation —> embryo— fetal liver,spleen and BM
After birth—> only in BM
How B cells exits BM
Immature ones at Endosteal niche
As they mature migration toward the vascular niche
Fully differentiated cells exit BM via BV
Phases of B cell development
1- Maturation phase — Foreign Ag Independent = Stem cell to mature-naive B cell
2-Differentiation phase— Foreign Ag dependent = Activated B- ab secreting Plasma or Memory B
Steps of maturation phase of B cell development
Stem cell—> Pro-B—> Pre-B—>Immature B—>Mature B
Which B cell type express enzyme RAG1/2 and TdT
Pro-B cell
DJ rearrangement starts in which phase
Latest stage of pro-B cell
Role of Surrogate Light chain in Pre-B cells
SLC binds to Cytosolic IgH and transfer IgH to membrane
Allelic Exclusion
Expression of a gene on one chromosome prevents expression of the allele on the second chromosome
Causes homogenous B cell receptors
Check points of B cells in BM
First check point caused by no pre-B cell receptor which results with apoptosis — Selects for functional heavy chains
Second checkpoint caused by no B-cell receptor which resulted with apoptosis — Selects functional light chains
Who makes the functional IgM
Immature B cell
If Immature B cells are auto reactive :
Undergo apoptosis — Negative selection, Clonal deletion
Receptor editing — avoiding negative selection
After positive selection B cell expresses
IgM
IgD
What happens when negative selection occurs
Immature B cell is retained in BM
Transition of Type 1 to Type 2 immature B cells derived by
BAFF
B Lymphocyte Activating Factor
What happens in the Early ProB part of the Maturation phase
DJ H chain recombination
Start of VDJ H chain recombination
What happens in the ProB or PreB part of Maturation phase
Complete VDJ H chain recombination
Clonal expansion
VJ L chain recombination
What happens in the Immature B part of the Maturation phase
Negative selection — Deletion, Receptor editing
T dependent type of B cell antigens
Needs presentation
Must contain a protein component
Before presentation it is active but no Clonal expansion
After presentation Clonal expansion and differentiation both occurs
T-independent type of B antigen
Does not presentation
Can make Clonal expansion, differentiation
Multivalent
After B cells leave BM and enter circulation they migrate through ;
Secondary Lymphoid organs and survey for ag
How does T cells help to B cells
B cells present ag with a MHC molecule to activated CD4 T cell
CD4 T cell express CD40L on its cell surface
CD40L binds to CD40 on the surface of the B cell
B cell express cytokine receptors
T cell secrete cytokines
With cytokines T cells instruct B cells on type of ab to produce
Cytokine types that T cell secrets to help B cells
IL-4
IL-5
IL-6
IFN-gamma
TGF-beta
If T cell secretes IL-4 and IL-5 which isotope of Ig will be secreted
IgE
If T cells secrete IFN-gamma which isotope of Ig will be secreted
IgG
