Marginal zone B cells are noncirculating mature B cell

B cell

B cells are lymphocytes that play a large role in the humoral immune response . The principal functions of B cells are to make antibodies against antigens, perform the role of antigen-presenting cells and eventually develop into memory B cells after activation by antigen interaction...

s that segregate anatomically into the marginal zone

Marginal zone

The marginal zone is the region at the interface between the non-lymphoid red pulp and the lymphoid white-pulp of the spleen. A marginal zone also exists in lymph nodes.-Composition and markers:It is composed of cells derived...

 (MZ) of the spleen

Spleen

The spleen is an organ found in virtually all vertebrate animals with important roles in regard to red blood cells and the immune system. In humans, it is located in the left upper quadrant of the abdomen. It removes old red blood cells and holds a reserve of blood in case of hemorrhagic shock...

. This region contains multiple subtypes of macrophage

Macrophage

Macrophages are cells produced by the differentiation of monocytes in tissues. Human macrophages are about in diameter. Monocytes and macrophages are phagocytes. Macrophages function in both non-specific defense as well as help initiate specific defense mechanisms of vertebrate animals...

s, dendritic cell

Dendritic cell

Dendritic cells are immune cells forming part of the mammalian immune system. Their main function is to process antigen material and present it on the surface to other cells of the immune system. That is, dendritic cells function as antigen-presenting cells...

s, 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. The MZ B cells within this region typically express high levels of sIgM

IGM

IGM as an acronym or abbreviation can refer to:* Immunoglobulin M , the primary antibody against A and B antigens on red blood cells* International Grandmaster, a chess ranking* intergalactic medium* Intragroup medium - see: Intracluster medium...

, CD21, CD1

CD1

For the album by Throbbing Gristle, see CD1 CD1 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 cells...

, CD9

CD9

CD9 antigen is a protein that in humans is encoded by the CD9 gene.-Interactions:CD9 has been shown to interact with TSPAN4, PTGFRN, CD81, CD117, CD46, CD29 and CD49c.-Further reading:...

 with low to negligible levels of sIgD

IGD

IGD can refer to:*Internet Gateway Device as defined in UPnP.*İGD, İlerici Gençler Derneği, Progressive Young Association of Turkey*Immunoglobulin D, an antibody protein involved in the maturation of B cells....

, CD23

CD23

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

, CD5

CD5

CD5 or CD-5 may be:* Child development-5, for five-year old children, a more developmentally appropriate acronym for kindergarten* cluster of differentiation 5 molecule, type I transmembrane protein* compact disc, 5-inch CD, usually music CD...

, 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

T cell

T cells or T lymphocytes belong to a group of white blood cells known as lymphocytes, and play a central role in cell-mediated immunity. They can be distinguished from other lymphocytes, such as B cells and natural killer cells , by the presence of a T cell receptor on the cell surface. They are...

 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. It is believed they are especially reactive to bacterial cell wall components and self-antigens which are the products of aging. 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.

In specimens where the tyrosine kinase for Pyk-2

PTK2B

Protein tyrosine kinase 2 beta is an enzyme that in humans is encoded by the PTK2B gene.-Protein:-Interactions:PTK2B has been shown to interact with PTPN11, PTPN6, PITPNM1, Gelsolin, Src, GRIN2A, Ewing sarcoma breakpoint region 1, RB1CC1, TGFB1I1, NPHP1, BCAR1, FYN, DLG4, DLG3, DDEF2, Cbl gene, RAS...

 has been knocked-out, marginal zone B-cells will fail to develop while B-1 cell

B-1 cell

B-1 cells are a sub-class of B cell lymphocytes that are involved in the humoral immune response. They are not part of the adaptive immune system,as they have no memory, but otherwise, B-1 cells perform many of the same roles as other B cells: making antibodies against antigens and acting as...

s will still be present.

MZ B-cells are the only B-cells dependent on NOTCH2

NOTCH2

Neurogenic locus notch homolog protein 2 also known as notch 2 is a protein that in humans is encoded by the NOTCH2 gene.NOTCH2 is associated with Alagille syndrome and Hajdu–Cheney syndrome.- Function :Notch 2 a member of the notch family...

signaling for proliferation.