Within the

immune system The immune system is a network of biological processes that protects an organism from diseases. It detects and responds to a wide variety of pathogens, from viruses to parasitic worms, as well as cancer cells and objects such as wood splinte ...

, Follicular B cells (FO B cells) are a type of

B cell B cells, also known as B lymphocytes, are a type of white blood cell of the lymphocyte subtype. They function in the humoral immunity component of the adaptive immune system. B cells produce antibody molecules which may be either secreted o ...

that reside in primary and secondary lymphoid follicles (containing germinal centers) of secondary and tertiary lymphoid organs, including

spleen The spleen is an organ found in almost all vertebrates. Similar in structure to a large lymph node, it acts primarily as a blood filter. The word spleen comes .

and

lymph node A lymph node, or lymph gland, is a kidney-shaped organ of the lymphatic system and the adaptive immune system. A large number of lymph nodes are linked throughout the body by the lymphatic vessels. They are major sites of lymphocytes that includ ...

s. Antibody responses against proteins are believed to involve follicular B cell pathways in secondary lymphoid organs. Mature B cells from the spleen can be divided into two main populations: FO B cells, which constitute the majority, and marginal zone B-cells, lining outside the marginal sinus and bordering the

red pulp The red pulp of the spleen is composed of connective tissue known also as the cords of Billroth and many splenic sinusoids that are engorged with blood, giving it a red color. Its primary function is to filter the blood of antigens, microorgan ...

. FO B cells express high levels of

IgD Immunoglobulin D (IgD) is an antibody isotype that makes up about 1% of proteins in the plasma membranes of immature B-lymphocytes where it is usually co-expressed with another cell surface antibody called IgM. IgD is also produced in a secreted ...

, and CD23; lower levels of CD21 and IgM; and no

CD1 CD1 (cluster of differentiation 1) is a family of glycoproteins expressed on the surface of various human antigen-presenting cells. They are related to the class I MHC molecules, and are involved in the presentation of lipid antigens to T ce ...

or CD5, 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 peripheral

lymph nodes A lymph node, or lymph gland, is a kidney-shaped organ of the lymphatic system and the adaptive immune system. A large number of lymph nodes are linked throughout the body by the lymphatic vessels. They are major sites of lymphocytes that includ ...

. 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. Recent studies indicate movement along the processes of FDC as a guidance system for mature resting B cells in peripheral lymph nodes. Unlike their MZ 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 dependent T_FH cell help to promote effective primary immune responses and antibody isotype switching 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.

References

{{Lymphocytes B cells Human cells Immune system Lymphocytes