Marginal zone

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Marginal zone
Illu spleen.jpg
Identifiers
FMA 15852
Anatomical terminology

The marginal zone is the region at the interface between the non-lymphoid red pulp and the lymphoid white-pulp of the spleen. (Some sources consider it to be the part of red pulp which borders on the white pulp, while other sources consider it to be neither red pulp nor white pulp.)

Contents

A marginal zone also exists in lymph nodes. [1]

Structure

Histology of a normal lymphoid follicle, with marginal zone annotated at bottom. Dark, light, mantle and marginal zones of a secondary follicle.png
Histology of a normal lymphoid follicle, with marginal zone annotated at bottom.

It is composed of cells derived primarily from the myeloid compartment of bone marrow differentiation. More recently, a population of neutrophil-killers has been described to populate peripheral areas of the marginal zone. [2] At least three distinct cellular markers can be used to identify cells of the marginal zone, MOMA-1, ERTR-9 and MARCO.

Blood flow

The marginal zone (MZ) is a highly transited area that receives large amounts of blood from the general circulation. Remarkably, the splenic microvasculature shows striking differences in mice and humans. In humans, the spleen receives blood from the splenic artery, which branches into central and penicillar arterioles. [3] Owing to the absence of a histologically defined marginal sinus, the blood flowing in penicillar arterioles directly drains into capillaries of the red pulp and perifollicular zone. The perifollicular zone is a well-defined area of decreased resistance that separates the MZ from the red pulp. Both the perifollicular zone and the red pulp consist of an open circulatory system of blood-filled spaces known as splenic cords, which have no defined endothelial delimitation and are in close contact with the venous sinusoidal vessels of the red pulp. [4]

Function

The major role of marginal zone is to trap particulate antigen from the circulation and present the antigen to the lymphocytes of the spleen.

Experiments have shown that inert latex beads as well as live bacteria such as Escherichia coli and Listeria monocytogenes are trapped by the marginal zone. However, only immunogenic substances, i.e. bacteria, are trafficked to the T and B cell zones of the white-pulp and are efficiently presented to elicit an immune response.

Lymphocytes

Marginal zone lymphocytes are a type of B cell (Marginal-zone B cell, abbreviated "MZ B cell") created there, capable of binding IgM-antigen complexes. They are notable for their ability to serve several different roles in the immune system. MZ B cells express polyreactive BCRs that bind to multiple microbial molecular patterns. [5]

Marginal zone macrophages

Within the marginal zone there exists two types of macrophages that are unique to this area: the marginal zone macrophages and the marginal metallophilic macrophages. These two macrophage sub-types are characterized by the expression of SIGN-R1 on the marginal zone macrophages and CD169 (siglec-1, sialoadhesin) on the marginal metallophilic macrophages.

In addition to the marginal zone B-cells that normally reside there, a number of other cell types that are present in the blood pass through the marginal zone e.g. lymphocytes and granulocytes. In addition, a large number of dendritic cells are thought to reside temporarily in the marginal zone before migrating into the white pulp following stimulation and antigen uptake, as well as a large number of lymphocytes remaining in the marginal zone for a period of time during the process of transmigration into the white pulp. It can be assumed that both of these cells will interact with the marginal zone macrophages.

Recent studies have shown that the marginal zone macrophages possess both important innate functions, as well as being able to promote adaptive immune responses, so these macrophages can bridge the innate and adaptive immunity.

The marginal zone macrophages have a variety of functions, one of which is the phagocytosis of blood-borne pathogens. Because of the anatomy of the marginal zone, the blood within it slows down and therefore the pathogens present in the systemic circulation are phagocytosed by both marginal zone macrophages. There is limited data regarding the specific roles of these two macrophage subsets in the uptake and eradication of pathogens. However there is evidence and reports that show there is a specific involvement of the various pathogen receptors on the marginal zone macrophages in recognising and eliminating certain pathogens, especially encapsulated bacteria. For example, the C-type lectin SIGN-R1 receptor (present on the marginal zone macrophages), mediates the recognition of pneumococcal saccharides and is necessary for Streptococcus pneumoniae clearance.

Furthermore, both types of marginal zone macrophages in the clearance and degradation of viruses e.g. cowpox virus and adenovirus serotype 5. Evidence has shown that the clearance of lymphocytic choriomeningitis virus by marginal zone macrophages is crucial to prevent the spreading of viral infections to peripheral organs. [6]

See also

Related Research Articles

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<span class="mw-page-title-main">Immunology</span> Branch of medicine studying the immune system

Immunology is a branch of medicine and biology that covers the medical study of immune systems in all organisms. In such we can see there is a difference of human immunology and comparative immunology in veterinary medicine and animal biosciences.

<span class="mw-page-title-main">Spleen</span> Internal organ in all vertebrates

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 from Ancient Greek σπλήν (splḗn).

<span class="mw-page-title-main">Lymphatic system</span> Organ system in vertebrates

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An immune response is a physiological reaction which occurs within an organism in the context of inflammation for the purpose of defending against exogenous factors. These include a wide variety of different toxins, viruses, intra- and extracellular bacteria, parasites, and fungi which could cause serious problems to the health of the host organism if not cleared from the body.

<span class="mw-page-title-main">B cell</span> Type of white blood 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 or inserted into the plasma membrane where they serve as a part of B-cell receptors. When a naïve or memory B cell is activated by an antigen, it proliferates and differentiates into an antibody-secreting effector cell, known as a plasmablast or plasma cell. Additionally, B cells present antigens and secrete cytokines. In mammals, B cells mature in the bone marrow, which is at the core of most bones. In birds, B cells mature in the bursa of Fabricius, a lymphoid organ where they were first discovered by Chang and Glick, which is why the 'B' stands for bursa and not bone marrow as commonly believed.

<span class="mw-page-title-main">Lymphocyte</span> Subtype of white blood cell

A lymphocyte is a type of white blood cell (leukocyte) in the immune system of most vertebrates. Lymphocytes include natural killer cells, T cells, and B cells. They are the main type of cell found in lymph, which prompted the name "lymphocyte". Lymphocytes make up between 18% and 42% of circulating white blood cells.High lymphocyte denotes that our system is dealing with an infection or other inflammatory condition.

<span class="mw-page-title-main">Cell-mediated immunity</span> Immune response that does not involve antibodies

Cell-mediated immunity or cellular immunity is an immune response that does not involve antibodies. Rather, cell-mediated immunity is the activation of phagocytes, antigen-specific cytotoxic T-lymphocytes, and the release of various cytokines in response to an antigen.

In immunology, the mononuclear phagocyte system or mononuclear phagocytic system (MPS) also known as the reticuloendothelial system or macrophage system is a part of the immune system that consists of the phagocytic cells located in reticular connective tissue. The cells are primarily monocytes and macrophages, and they accumulate in lymph nodes and the spleen. The Kupffer cells of the liver and tissue histiocytes are also part of the MPS. The mononuclear phagocyte system and the monocyte macrophage system refer to two different entities, often mistakenly understood as one.

<span class="mw-page-title-main">Adaptive immune system</span> Subsystem of the immune system that is composed of specialized, systemic cells and processes

The adaptive immune system, also known as the acquired immune system, or specific immune system is a subsystem of the immune system that is composed of specialized, systemic cells and processes that eliminate pathogens or prevent their growth. The acquired immune system is one of the two main immunity strategies found in vertebrates.

Gut-associated lymphoid tissue (GALT) is a component of the mucosa-associated lymphoid tissue (MALT) which works in the immune system to protect the body from invasion in the gut.

<span class="mw-page-title-main">Innate immune system</span> One of the two main immunity strategies

The innate, or nonspecific, immune system is one of the two main immunity strategies in vertebrates. The innate immune system is an alternate defense strategy and is the dominant immune system response found in plants, fungi, insects, and primitive multicellular organisms.

<span class="mw-page-title-main">White pulp</span> Type of tissue in the spleen

White pulp is a histological designation for regions of the spleen, that encompasses approximately 25% of splenic tissue. White pulp consists entirely of lymphoid tissue.

<span class="mw-page-title-main">Red pulp</span> Type of tissue in the spleen

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, microorganisms, and defective or worn-out red blood cells.

Splenic marginal zone lymphoma (SMZL) is a type of cancer made up of B-cells that replace the normal architecture of the white pulp of the spleen. The neoplastic cells are both small lymphocytes and larger, transformed lymphoblasts, and they invade the mantle zone of splenic follicles and erode the marginal zone, ultimately invading the red pulp of the spleen. Frequently, the bone marrow and splenic hilar lymph nodes are involved along with the peripheral blood. The neoplastic cells circulating in the peripheral blood are termed villous lymphocytes due to their characteristic appearance.

A non-specific immune cell is an immune cell that responds to many antigens, not just one antigen. Non-specific immune cells function in the first line of defense against infection or injury. The innate immune system is always present at the site of infection and ready to fight the bacteria; it can also be referred to as the "natural" immune system. The cells of the innate immune system do not have specific responses and respond to each foreign invader using the same mechanism.

The following outline is provided as an overview of and topical guide to immunology:

<span class="mw-page-title-main">Marginal zone B-cell</span>

Marginal zone B cells are noncirculating mature B cells that in humans segregate anatomically into the marginal zone (MZ) of the spleen and certain other types of lymphoid tissue. The MZ B cells within this region typically express low-affinity polyreactive B-cell receptors (BCR), high levels of IgM, Toll-like receptors (TLRs), CD21, CD1, CD9, CD27 with low to negligible levels of secreted-IgD, CD23, CD5, and CD11b that help to distinguish them phenotypically from follicular (FO) B cells and B1 B cells.

Within the immune system, Follicular B cells are a type of B cell that reside in primary and secondary lymphoid follicles of secondary and tertiary lymphoid organs, including spleen and lymph nodes. Antibody responses against proteins are believed to involve follicular B cell pathways in secondary lymphoid organs.

B10 cells are a sub-class of regulatory B-cells that are involved in inhibiting immune responses in both humans and mice. B10 cells are named for their ability to produce inhibitory interleukin: Interleukin-10 (IL-10). One of their unique abilities is that they suppress the innate and adaptive immune signals, making them important for regulating the inflammatory response. Like the B cell, the B10 cell requires antigen specific binding to the surface of CD5 receptor to illicit a response from the T-cell. Once an antigen binds to the CD19 receptor, immediate downregulation in B-cell receptor (BCR) signal expression occurs and mediates the release of IL-10 cytokines. In mice and humans, B10 cells are distinguishable in their expression of measurable IL-10 due to the lack of unique cell surface markers expressed by regulatory B cells. However, IL-10 competence is not limited to any one subset of B cells. B10 cells do not possess unique phenotypic markers or transcription factors for further identification. B10 cells predominantly localize in the spleen, though they are also found in the blood, lymph nodes, Peyer's patches, intestinal tissues, central nervous system, and peritoneal cavity. B10 cells proliferate during inflammatory and disease responses.

References

  1. ↑ "Lymph nodes & spleen, nonlymphoma".
  2. ↑ Puga, Irene; Cols, Montserrat; Barra, Carolina M; He, Bing; Cassis, Linda; Gentile, Maurizio; Chen, Kang; Cerutti, Andrea (December 2011). "B cell–helper neutrophils stimulate the diversification and production of immunoglobulin in the marginal zone of the spleen". Nature Immunology. 13 (2): 170–80. doi:10.1038/ni.2194. PMC   3262910 . PMID   22197976.
  3. ↑ Mebius, Reina E.; Kraal, Georg (August 2005). "Structure and function of the spleen". Nature Reviews Immunology. 5 (1): 606–616. doi:10.1038/nri1669. PMID   16056254. S2CID   3258595.
  4. ↑ Steiniger, Birte; Timphus, Eva Maria; Barth, Peter J. (December 2006). "The splenic marginal zone in humans and rodents: an enigmatic compartment and its inhabitants". Histochemistry and Cell Biology. 126 (6): 641–648. doi:10.1007/s00418-006-0210-5. PMID   16816939. S2CID   31943597.
  5. ↑ Martin, Flavius; Kearney, John F. (May 2002). "Marginal-zone B cells". Nature Reviews Immunology. 2 (5): 323–35. doi:10.1038/nri799. PMID   12033738. S2CID   22573840.
  6. ↑ den Haan, Joke M.M.; Kraal, Georg (2012). "Innate Immune Functions of Macrophage Subpopulations in the Spleen". Journal of Innate Immunity. 4 (5–6): 437–445. doi:10.1159/000335216. ISSN   1662-8128. PMC   6741446 . PMID   22327291.
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