Marginal-zone B cell

Marginal-zone B cells are noncirculating mature B cells that segregate anatomically into the marginal zone (MZ) of the spleen. [Martin F, Kearney JF. Marginal-zone B cells. Nat Rev Immunol. 2002;2(5):323–335.] This region contains multiple subtypes of macrophages, dendritic cells, and the MZ B cells; it is not fully formed until 2 to 3 weeks after birth in rodents and 1 to 2 years in humans. [MacLennan IC, Bazin H, Chassoux D, et al. Comparative analysis of the development of B cells in marginal zones and follicles. Adv Exp Med Biol. 1985;186:139–144.] The MZ B cells within this region typically express high levels of sIgM, CD21, CD1, CD9 with low to negative levels of sIgD, CD23, CD5, and CD11b that help to distinguish them phenotypically from FO B cells and B1 B cells.

Similar to B1 B cells, MZ B cells can be rapidly recruited into the early adaptive immune responses in a T cell independent manner. The MZ B cells are especially well positioned as a first line of defense against systemic blood-borne antigens that enter the circulation and become trapped in the spleen. [ Balazs M, Martin F, Zhou T, et al. Blood dendritic cells interact with splenic marginal zone B cells to initiate T-independent immune responses. Immunity. 2002;17(3):341–352.] MZ B cells also display a lower activation threshold than their FO B cell counterparts with heightened propensity for PC differentiation that contributes further to the accelerated primary antibody response. [Lopes-Carvalho T, Foote J, Kearney JF. Marginal zone B cells in lymphocyte activation and regulation. Curr Opin Immunol. 2005; 17(3):244–250]

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