Memory B cell

In immunology, a memory B cell (MBC) is a type of B lymphocyte that forms part of the adaptive immune system.

[5] B cells may also be activated by binding foreign antigen in the periphery where they then move into the secondary lymphoid organs.

Within the secondary lymphoid organs, most of the B cells will enter B-cell follicles where a germinal center will form.

[7][8] Class switching allows memory B cells to secrete different types of antibodies in future immune responses.

The activated B cells that expressed the transcription factor Bcl-6 will enter B-cell follicles and undergo germinal center reactions.

[7] Once inside the germinal center, the B cells undergo proliferation, followed by mutation of the genetic coding region of their BCR, a process known as somatic hypermutation.

[6] These processes increase variability at the antigen binding sites such that every newly generated B cell has a unique receptor.

[11] After differentiation, memory B cells relocate to the periphery of the body where they will be more likely to encounter antigen in the event of a future exposure.

[6][2][3] Many of the circulating B cells become concentrated in areas of the body that have a high likelihood of coming into contact with antigen, such as the Peyer's patch.

[6][4] Other hypotheses propose that the transcription factor NF-κB and the cytokine IL-24 are involved in the process of differentiation into memory B cells.

[4] However, it is true that the lifespan of individual memory B cells remains poorly defined, although they have a critical role in long-term immunity.

In one study using a B cell receptor (BCR) transgenic system (it was a H chain transgenic mouse model which lacked secreted Ig, so it didn´t deposit Ag-containing immune complexes), it was shown that the number of memory B cells remain constant for a period of around 8–20 weeks after the immunization.

Moreover, the signal produce by TLR4 when it is stimulated by natterins (protein obtained from T. nattereri fish venom) accelerates the synthesis of the antibody IgE acting as an adjuvant, as it was shown in an in vivo experiment with mice.

Memory B cells may have this receptor to allow them to move out of the germinal center and into the tissues where they have a higher probability of encountering antigen.

T-bet B cells are also thought to be important in immune responses against intracellular bacterial and viral infections.

The preventative injection of a non-pathogenic antigen into the organism allows the body to generate a durable immunological memory.

These memory B cells are promptly reactivated upon infection with the antigen and can effectively protect the organism from disease.