slides on B-lymphocytes

2. GROUP NO. 2
• DUR-E-NAYAB(036)
• UMBER NOOR(023)
• MARIA ASGHAR(019)
• ATTA-UL-MUSTAFA(031)
• SHAHZAIB MAQSOOD(015)
• ASIM SHEHZAD(020)

3. B- LYMPHOCYTES
-GENERATION
-DIFFERENCIATION
-MATURATION
-ACTIVATION

4. B-LYMPHOCYTES
• They comprises 30% of lumphicytes circulating in blood.
• About 1 billion B-cell are produced daily.
• They are majorly present in spleen.
• Their life span is days to weeks unless exposed by any antigen.

5. B-CELL GENERATION
• B-cell development starts in bone marrow by totipotent
hematologic stem cell.
• Two genes are involved:RAG1 and RAG2.

6. B cell development in the bone marrow
B Regulates construction of an antigen receptor
Bone Marrow provides a
MATURATION & DIFFERENTIATION MICROENVIRONMENT
for B cell development
Ensures each cell has only one specificityB
Checks and disposes of self-reactive B cellsB
Exports useful cells to the peripheryB
Provides a site for antibody productionB

7. Peripheral
Stages of B cell development
Stem Cell Early pro-B cell Late pro-B cell Large pre-B cell
Small pre-B cell Immature B cell Mature B cell
Each stage of development is defined by rearrangements of IgH chain
genes, IgL chain genes, expression of surface Ig, expression of
adhesion molecules and cytokine receptors

8. Early pro-
B
Kit
Receptor Tyrosine
kinase
Stem cell factor
Cell-bound
growth
factor
VLA-4
(Integrin)
Stem
Cytokines and cell-cell contacts at each stage of
differentiation are different
Stromal cell
Cell adhesion
molecules
VCAM-1
(Ig superfamily)

9. Early pro-
B
Interleukin-7
receptor
Stromal cell
Late pro-
B Pre-B
Interleukin-7
Growth factor
Cytokines and cell-cell contacts at each stage of
differentiation are different

10. Stages of differentiation in the bone marrow are
defined by Ig gene rearrangement
B CELL STAGE
IgH GENE
CONFIGURATION
Stem cell Early pro-B Late pro-B Large pre-B
Germ line DH to JH VH to DHJH VHDHJH
Pre-B cell
receptor
expressed
Ig light chain gene has not yet rearranged

11. GENE ARRANGEMENT
Heavy chain gene rearrangement
• Light chain gene rearrangement

12. Large
Pre-B
Large
Pre-B
Large
Pre-B
Large
Pre-B Large
Pre-B
Large
Pre-B Large
Pre-B
Large
Pre-B Large
Pre-B
Large
Pre-B
Proliferation
Y
Immature
B cell
Light chain expressed
IgM displayed on surface
IgM
Ligation of the pre-B cell receptor triggers entry
into the cell cycle
Large
pre-B
Many large pre-B cells
with identical pre-B
receptors
Large
pre-B
Intracellular VDJCH chain
VL-JL rearranges
Proliferation
stops
Pre-receptor
not displayed
Small
pre-B

13. B cell recognises
non-self antigen
in periphery
Ig-secreting plasma cell
Differentiation in the periphery
YY
YY
YY
B
Y YB
Y YB
Mature peripheral
B cell

15. B-CELL MATURATION
• Activation,poliferation and differentiation of b-cell occur in
bone marrow and require antigen.
• Antigen dependent activation and clonal selection leads to
naïve B-cell leads to generation of plasma cells and memory B-
cells.
• Ag independent activation-naïve B-cells inn periphery have a
short life span.

17. ANTIGEN INDEPENDENT
MATURATION
• Pro B-cell differentiate into pre B-cell by several interactions
with stromal cell.
• Interactions are:
1. VCAM-1 ligand of stromal cell and VLA-4of pro B-cell.
2. Binding of C-kit of pro B-cell and SCF of stromal cell , that
triggers a signal mediated by tyrosine kinase activity of C-kit.
3. ILR-7 is exposed by pro B-cell that binds with IL-7 released by
stromal cell.
after that pro B-cellpre B-cell ,detach from stromal
cell.

19. ANTIGEN DEPENDENGT
MATURATION
• Pre B-cell naïve cell
• Naïve cell(express IgM and IgD) receive competence and
progression signal from antigen and T helper cell(IL4:B-cell
growth factor,IL5:B-cell expansion factor) and enter cell cycle
and then differentiate into plasma cells ,memory cells.
• class switching

20. Clonal selection and expansion

21. B-cell activation
• They are activated by two different routes depending on thymus
dependent and independent Ag.
thymus dependent Ag
Direct interaction with T
helper cells
Ag(soluble proteins)
Exhibit immunological
memory and strong response
High level of Ig isotypes
switching
thymus independent Ag
Need cytokine sometimes(no
direct interaction)
Ag (bacterial cell wall
components)
Weak response no
immunological memory
Low level of class switching

23. T helper cell activation

24. Thymus independent Ag activation
Type 1
Polyclonal b-cell activation with the Ag
specificity(when Ag are in high
concentration)
Antigens are: bacterial cell wall
components -LPS
Type 2
Ag specific activation and need cytokines
too
Antigens are :repetitive molecules-
bacterial polysaccrides,
Bacterial flagella(protein)

25. B-CELL DIFFERENTIATION
• High affinity centroblast will survive due to improved affinity
maturation via beneficial mutation.
• Centrocytes will successfully make contact with antigen and
switch class(IgD/IgmIgE/IgG/IgA) followed by cell
differentiation into plasma cells and memory B-cells.

26. How can B cells express
IgM and IgD simultaneously?
Ca2CeCg4Cg2Ca1Cg1Cg3CdCm
Cm
Cd
Cg3VDJ
Sg3
Cm
Cd
Cg3
VDJ
Cg1
Sg1
Ca1
Cg3
VDJ Ca1
Cg3VDJ
IgG3 produced.
Switch from IgM
VDJ Ca1
IgA1 produced.
Switch from IgG3
VDJ Ca1
IgA1 produced.
Switch from IgM
N.B. Remember Molecular Genetics of Immunoglobulins lecture – No Cd switch region
Consider similarities with mechanism allowing secreted and membrane Ig by the same cell

27. Class switching

28. OVER VIEW

29. OVER VIEW

30. Uth Jao…….:-@
Lecture muck Gaya hay……… :-p