Within the

immune system The immune system is a network of biological systems that protects an organism from diseases. It detects and responds to a wide variety of pathogens, from viruses to bacteria, as well as Tumor immunology, cancer cells, Parasitic worm, parasitic ...

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

B cell B cells, also known as B lymphocytes, are a type 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 or inserted into the plasm ...

that reside in primary and secondary lymphoid follicles (containing

germinal center Germinal centers or germinal centres (GCs) are transiently formed structures within B cell zone (follicles) in secondary lymphoid organs – lymph nodes, ileal Peyer's patches, and the spleen – where mature B cells are activated, prolifera ...

s) of secondary and tertiary lymphoid organs, including

spleen The spleen (, from Ancient Greek '' σπλήν'', splḗn) is an organ (biology), organ found in almost all vertebrates. Similar in structure to a large lymph node, it acts primarily as a blood filter. The spleen plays important roles in reg ...

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 The marginal sinus is a dural venous sinus surrounding the margin of the foramen magnum inside the skull, accommodated by the groove for marginal sinus. It usually drains into either the sigmoid sinus, or the jugular bulb. It communicates with th ...

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, microorganis ...

. FO B cells express high levels of IgD, and

CD23 CD23, also known as Fc epsilon RII, or FcεRII, is the "low-affinity" biochemistry, receptor for IgE, an antibody isotype involved in allergy and resistance to parasitism, parasites, and is important in regulation of IgE levels. Unlike many of the ...

; lower levels of

CD21 Complement receptor type 2 (CR2), also known as complement C3d receptor, Epstein–Barr virus receptor, and CD21 (cluster of differentiation 21), is a protein that in humans is encoded by the CR2 gene. CR2 is involved in the complement system. I ...

and

IgM Immunoglobulin M (IgM) is the largest of several isotypes of antibodies (also known as immunoglobulin) that are produced by vertebrates. IgM is the first antibody to appear in the response to initial exposure to an antigen; causing it to also ...

; and no

CD1 CD1 (cluster of differentiation 1) is a family of glycoproteins expressed on the surface of various human antigen-presenting cells. CD1 glycoproteins are structurally related to the class I MHC molecules, however, in contrast to MHC class ...

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 (anatomy), 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 lymphoc ...

. 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.

References

{{Lymphocytes B cells Human cells Immune system Lymphocytes