Mononuclear phagocyte system
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.
Cell types and locations
The spleen is the largest unit of the mononuclear phagocyte system. The monocyte is formed in the bone marrow and transported by the blood; it migrates into the tissues, where it transforms into a histiocyte or a macrophage.
Macrophages are diffusely scattered in the connective tissue and in liver (Kupffer cells), spleen and lymph nodes (sinus histiocytes), lungs (alveolar macrophages), and central nervous system (microglia). The half-life of blood monocytes is about 1 day, whereas the life span of tissue macrophages is several months or years. The mononuclear phagocyte system is part of both humoral and cell-mediated immunity. The mononuclear phagocyte system has an important role in defense against microorganisms, including mycobacteria, fungi, bacteria, protozoa, and viruses. Macrophages remove senescent erythrocytes, leukocytes, and megakaryocytes by phagocytosis and digestion.
|Adipose tissue macrophages||Adipose tissue|
|Sinus histiocytes||Lymph node|
|Alveolar macrophage(dust cell)||Pulmonary alveolus of Lungs|
|Tissue macrophages (Histiocyte) leading to Giant cells||Connective Tissues|
|Langerhans cell||Skin and Mucosa|
|Microglia||Central Nervous System|
|Intraglomerular mesangial cell||Kidney|
|Red Pulp Macrophage (Sinusoidal lining cells)||Red pulp of Spleen|
|Peritoneal macrophages||Peritoneal cavity|
- Formation of new red blood cells (RBCs) and white blood cells (WBCs).
- Destruction of old RBCs and WBCs
- Formation of plasma proteins.
- Formation of bile pigments.
- Storage of iron. In the liver, Kupffer cells store excess iron from catabolism of heme from the breakdown of red blood cells. In bone marrow and spleen, iron is stored in MPS cells mostly as ferritin; in iron overload states, most of the iron is stored as hemosiderin.
- Clearance of Heparin via Heparinases