Follicular B Cells

The majority of mature B cells in the spleen express high levels of IgM, IgD, and CD23; lower C21; and no CD1 or CD5, readily distinguishing this FO B cell compartment from B1 B cells and MZ B cells. FO B cells organize into the primary follicles of B cell zones focused around follicular dendritic cells in the white pulp of the spleen and the cortical areas of peripheral lymph nodes. Multiphoton-based live imaging of lymph nodes indicate continuous movement of FO B cells within these follicular areas at velocites of ~6 µm per min. [Miller MJ, Wei SH, Parker I, et al. Two-photon imaging of lymphocyte motility and antigen response in intact lymph node. Science. 2002;296(5574):1869–1873.] Recent studies indicate movement along the processes of FDC as a guidance system for mature resting B cells in peripheral lymph nodes. [Bajenoff M, Egen JG, Koo LY, et al. Stromal cell networks regulate lymphocyte entry, migration, and territoriality in lymph nodes. Immunity. 2006;25(6):989–1001.] Unlike their MZ counterpart, FO B cells freely recirculate, comprising >95% of the B cells in peripheral lymph nodes.

The BCR repertoire of the FO B cell compartment also appears under positive selection pressures during final maturation in the spleen. However, diversity is substantially broader than B1 B and MZ B cell compartments. More importantly, FO B cells require CD40-CD40L dependent T cell help to promote effective primary immune responses and antibody isotype switch and to establish high-affinity B cell memory. [McHeyzer-Williams LJ, McHeyzer-Williams MG. Antigen-specific memory B cell development. Annu Rev Immunol. 2005;23:487–513.]

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