B cells are lymphocytes that play a large role in the humoral immune response (as opposed to the cell-mediated immune response, which is governed by T cells). The principal function of B cells is to make antibodies against soluble antigens.
how many and where ?
T and B
After reaching the IgM+ immature stage in the bone marrow, these transitional B cells migrate to the spleen where they mature into B lymphocytes.
B cell development occurs through several stages, each stage representing a change in the genome content at the antibody loci.
An antibody is composed of two light (L) and two heavy (H) chains, and the genes specifying them are found in the 'H' chain locus and the 'L' chain locus. In the H chain loci there are three regions, V, D and J, which recombine randomly, in a process called VDJ recombination, to produce a unique variable domain in the immunoglobulin of each individual B cell. Similar rearrangements occur for L chain locus except there are only two regions, namely V and J. The list below describes the process of immunoglobulin formation at the different stages of B cell development.
- Progenitor B cells - Contains Germline H genes, Germline L genes
- Early Pro-B cells - undergoes D-J rearrangement on the H chains
- Late Pro-B cells - undergoes V-DJ rearrangement on the H chains
- Large Pre-B cells - the H chain is VDJ rearranged, Germline L genes
- Small Pre-B cells - undergoes V-J rearrangement on the L chains
- Immature B cells - VJ rearranged on L chains, VDJ rearranged on H chains. There is start of expression of IgM receptors.
- Mature B cells - There is start of expression of IgD
B cells maturation
interesting project on B-cells development
When the B cell fails in any step of the maturation process, it will die by a mechanism called apoptosis.
If it recognizes self-antigen during the maturation process, the B cell will become suppressed (known as anergy) or undergo apoptosis (a process called negative selection).
B cells are continuously produced in the bone marrow, but only a small portion of newly made B cells survive to participate in the long-lived peripheral B cell pool.
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B cells images