Within theimmune system,follicular B cells (FO B cells) are a type ofB cell that reside in primary and secondary lymphoid follicles (containinggerminal centers) of secondary and tertiary lymphoid organs, includingspleen andlymph nodes. Antibody responses against proteins are believed to involve follicular B cell pathways in secondary lymphoid organs.[1]
Mature B cells from the spleen can be divided into two main populations: FO B cells, which constitute the majority, andmarginal zone B-cells, lining outside themarginal sinus and bordering thered pulp. FO B cells express high levels ofIgD, andCD23; lower levels ofCD21 andIgM; and noCD1 orCD5, readily distinguishing this compartment from B1 B cells and marginal zone 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 peripherallymph nodes. Multiphoton-based live imaging of lymph nodes indicate continuous movement of FO B cells within these follicular areas at velocities of ~6 μm per min.[2] Recent studies indicate movement along the processes ofFDC as a guidance system for mature resting B cells in peripheral lymph nodes.[3] Unlike theirMZ counterpart, FO B cells freely recirculate, comprising >95% of the B cells in peripheral lymph nodes.
The BCR repertoire of the follicular 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 dependentTFH cell help to promote effective primary immune responses and antibody isotype switching and to establish high-affinity B cell memory.[4]