There are two types of lymphocytes namely B-cells and T-cells, which are critical for the immune system. In addition, several accessory cells and effector cells also participate. The site of development and maturation of B-cells occurs in bursa fabricius in birds, and bone marrow in mammals. During the course of immune response. B-cells mature into plasma cells and secrete antibodies (immunoglobulins). The B-cells possess the capability to specifically recognize each antigen and produce antibodies (i.e. immunoglobulins) against it.

1. B lymphocytes-
Maturation and
Development
Bhanu Krishan

2. Table of Contents
Introduction to B cells
Development of B cells in Bone Marrow
Pre B cells and Pro B cells
Maturation of B cells
References

3. B Lymphocytes
 There are two types of lymphocytes namely B-cells and T-cells, which are critical for the
immune system.
 In addition, several accessory cells and effector cells also participate.
 The site of development and maturation of B-cells occurs in bursa fabricius in birds, and
bone marrow in mammals. During the course of immune response. B-cells mature into
plasma cells and secrete antibodies (immunoglobulins).
 The B-cells possess the capability to specifically recognize each antigen and produce
antibodies (i.e. immunoglobulins) against it.
Fig 1 – Blood film
showing a
multinucleated
plasma cell

4. Figure 1: B cell development stages from Hematopoietic Stem Cells
Source: British Society for Immunology

5. Development of B lymphocytes
 The development of B lymphocyte takes place in the bone marrow in humans and mice
 The development takes place in the fetal liver before birth and in the bone marrow
afterward (Hardy and Hayakawa, 2001).
 B cell development is a highly regulated process in which functional peripheral subsets are
produced from hematopoietic stem cells
 It takes around 1-2 weeks to develop from hematopoietic stem cells to mature B cells.
 Thus, Cellular homeostasis in the B cell compartment is strictly imposed to balance cell
production and cell loss ( Sahaf, et.al, 2016). Figure 2: B cell SEM Image
Source: Science Photo Library

6.  B-cell development begins in the bone marrow with the asymmetric division of an HSC
and continues through a series of progressively more differentiated progenitor stages to the
production of common lymphoid progenitors.
 Developmental progression is guided by sequential events leading to assembly, expression
and signalling of the B cell antigen receptor (BCR). Heavy (H) and light (L) chain
immunoglobulin genes are rearranged at the pro-B and pre-B stages (respectively), and
complete surface IgM is expressed at the immature stage.
 Further developmental progression and maturation in the periphery are limited by positive
and negative selection, mediated by BCR signalling and aiming to construct a non-self-
reactive and immune-competent repertoire of naïve B cells.

7. Figure 3: BCR signaling pathways important for transitional B cell development.
Source: doi:10.1016/j.cellimm.2006.04.007

8. B cell Development in Bone Marrow
 During B-cell development, bone marrow stromal cells fulfill two functions.
1. By interacting with adhesion molecules on the surfaces of HSCs and progenitor
cells, stromal cells retain the developing cell populations in the specific bone
marrow niches where they can receive the appropriate molecular signals required
for their further differentiation.
2. Diverse populations of stromal cells express different cytokines. At various points
in their development, progenitor and precursor B cells must interact with stromal
cells secreting particular cytokines, and thus the developing B cells move in an
orderly progression from location to location within the bone marrow.
 This progression is guided by chemokines secreted by particular stromal cell
populations.

9. Figure 4: Stages of development of B cells
Source: http://doi.org/10.1038/nri2133

10. Pre Pro B cells
 Pre Pro B cells expresses CD45R, a B-cell lineage-specific marker. hence they increase expression
of EBF-1 transcription factor.
 EBF-1 and E2A bind the Ig gene, promoting accessibility of D-JH locus, preparing for the 1st step
in Ig gene recombination. EBF-1 also important for expression of other B cell proteins, including
CD79α/β and genes encoding the pre-B cell receptor.
 When D-JH recombination is complete it requires IL-3, IL-7, insulin-like growth factor 1, stem cell
factor. Pax5 expression (target of EBF-1) – Master transcription factor (essential for all subsequent
stages of B cell development) that promotes VH to D recombination.
 RAG1 and RAG2 expression catalyzes the D-JH rearrangements within the Ig heavy chain gene
loci.
 Surface expression of CD19 – Component of multimolecular surface complex involved in
signalling in response to antigen and T cell help expression of HLA-DR and CD34 • By late pro-B
cell stage, most cells have initiated VH to DJH Ig gene segment recombination.

11. Pre B cells
 Ig heavy chain genes with complete V-D-J recombination – Allows surface expression of Ig heavy chain and
surrogate light chains complex called pre-B cell receptor
 CD79a and CD79b (Ig-α and Ig-β) associate non-covalently with surface Ig – signal
transducing components of the pre-B cell receptor – also components of the Ig receptors on the
surface of mature B cells.
 Signalling through the pre-B cell receptor induces a few rounds of proliferation;
at the end of this the pre-B cell receptor is lost from the surface late pre B cell stage.
 If pre B cell receptor cannot be displayed on cell surface because of non productive.
VHDJH gene rearrangement, then B cell development stops and the cell undergoes apoptosis,
Pre-B cell receptor signalling causes transient decrease in RAG1/2 and loss of Tdt.
 Light chain rearrangement is initiated following re-expression of RAG1/2. Figure 5: Pro B cell and Pre B cells development
Source: Boster Bio

12. Figure 6,7 : Generation of B cell with an overview of Gene arrangement and recombination
Source: British Society for Immunology

13. Figure 8: Bone Marrow B cells
Source: Dunn- Walters’ lab

14. B cell Maturation
 B cells complete maturation after migrating to the periphery, where they transit several
intermediate developmental stages prior to recruitment into the long-lived primary pool (
Cancro and Micheal, 2004).
 Mature B cells express antibodies on their surface, which are specific for a particular
antigen.
 The antibodies are expressed on the cell surface and are primarily IgM with some IgD.
 These cells circulate in the blood or home to sites of infection or inflammation. However,
until they are activated by T-cells, they do not proliferate or differentiate to form antibody
producing Plasma Cells (Micheal, 2014).

15. Mature B cells
 Mature B cells are the complete IgM molecule on cell surface.
 Mature resting B cells express HLA-DR, CD19, CD20, CD40 but no longer
express CD10, CD34, RAG1, RAG2, or Tdt.
 Pre- B cell Exit bone marrow, migrate to secondary lymphoid organs, then
express both surface IgM and IgD as well as other molecules that mediate cell-
cell and cell-ECM adhesive interactions.
 •These recirculate between blood and lymphoid organs, entering B cell follicles in
lymph nodes and spleen, responding to antigen encounter with T cell help, leading
to antibody production based upon the antigen.

16. Figure 9: Stages of B cell maturation
Source: (Edwards et.al, 2006) http://doi.org/10.1038/nri1838

17. References
 Hardy, Richard R., and Kyoko Hayakawa. "B cell development pathways." Annual review of immunology 19.1 (2001): 595-621.
 Thomas, Matthew D., Bhaskar Srivastava, and David Allman. "Regulation of peripheral B cell maturation." Cellular
immunology 239.2 (2006): 92-102.
 Cancro, Michael P. "Peripheral B‐cell maturation: the intersection of selection and homeostasis." Immunological reviews 197.1
(2004): 89-101.
 M, Mills. “Immunological and Inflammatory Aspects of Periodontal Disease.” Dental Care (2004).
 Cambier, John & Gauld, Stephen & Merrell, Kevin & Vilen, Barbara. (2007). B-cell anergy: From transgenic models to naturally
occurring anergic B cells?. Nature reviews. Immunology. 7. 633-43. 10.1038/nri2133
 Edwards, Jonathan & Cambridge, Geraldine. (2006). Edwards JC, Cambridge GB-cell targeting in rheumatoid arthritis and other
autoimmune diseases. Nat Rev Immunol 6:394-403. Nature reviews. Immunology. 6. 394-403. 10.1038/nri1838..
 Punt, Jenni, Sharon A. Stranford, Patricia P. Jones, and Judith A. Owen. Kuby Immunology. , 2019. 8th Edition