Reticuloendothelial system
 | It has been suggested that this article be merged into Mononuclear phagocyte system. (Discuss) Proposed since May 2019. |
The term “the reticuloendothelial system” (abbreviated RES) was originally launched in beginnings of the 20 century to denote a system of specialized cells that effectively clear colloidal stains (called “vital stains” because they stain living cells) from the blood circulation. The term is still used today, but its meaning has changed over the years, and is used in at least two different ways in the present literature, which causes confusion.[citation needed]
Structure
RES describe a network of cells and tissues that take up particles and vital dyes. The prefix “reticulo” (from Latin reticulum) meaning network. The most important RES cells are lining the sinusoids of the liver, spleen, and bone marrow, in addition to reticular cells of lymphatic tissue.
History
In the 1920s, the founder of the term RES, Ludwig Aschoff, reviewed the field of vital staining, and concluded that the cells lining the liver sinusoids, lymph sinuses, and the capillaries of the adrenals, pituitary and bone marrow comprised by far the most active part of the RES.[1] It should be noted that at the time when RES was launched, the understanding of concepts like endothelium, macrophages and phagocytosis were still under development, and during the centennium that followed there has been a considerable change in the way we understand these terms today.
The RES confusion
During the years that followed after Aschoff had launched the concept of RES, research on macrophages and their feature as professional phagocytes steadily increased, and in 1960 the concept of the mononuclear phagocyte system (MPS) was proposed to denote all kinds of macrophages. Functionally the cells of MPS share the function of clearing particles like bacteria, fungi, viruses, and dying cells from the circulation. Since blood clearance is also a signature function of cells of RES, scientists at the time implicated that RES is identical to MPS, and it was proposed that the term RES be replaced with MPS.[2]
During the 1980s and 1990s some laboratories noted that specialized endothelial cells (called scavenger endothelial cells), but not macrophages, were responsible for the avid clearance of macromolecules and nanoparticles from the blood circulation. This triggered a re-evaluation of the well-established notion that RES = MPS. In 1998 experiments were carried out to repeat the studies of Aschoff, following exactly the original methods description, and using modern ways of identifying the cells that were responsible for clearance of intravascularly injected colloidal litium carmine, the most commonly used vital stain. The studies showed that the cell system that Aschoff described as RES in the liver were in fact sinusoidal liver endothelial cells (LSECs), but not liver macrophages (Kupffer cells).[3]
In most contemporary text books and many articles that are still published the authors still use the term RES,[citation needed] implicating that it is synonymous with MPS. This is especially unfortunate when discussing e.g. blood clearance of nano formulations. Refraining from including the highly active scavenger endothelium when discussing blood clearance may lead to failure to understand the mechanisms of clearance of several substances from the circulation.[citation needed]
See also
References
- ^ Aschoff, L. (1924). "Das reticulo-endotheliale System". Ergebnisse der Inneren Medizin und Kinderheilkunde: Sechsundzwanzigster Band (in German). Springer Berlin Heidelberg: 1–118. doi:10.1007/978-3-642-90639-8_1.
- ^ van Furth, R; Cohn, ZA; Hirsch, JG; Humphrey, JH; Spector, WG; Langevoort, HL (1972). "The mononuclear phagocyte system: a new classification of macrophages, monocytes, and their precursor cells". Bulletin of the World Health Organization. 46 (6): 845–52. PMID 4538544.
- ^ Kawai, Y; Smedsrød, B; Elvevold, K; Wake, K (May 1998). "Uptake of lithium carmine by sinusoidal endothelial and Kupffer cells of the rat liver: new insights into the classical vital staining and the reticulo-endothelial system". Cell and tissue research. 292 (2): 395–410. PMID 9560481.
External links
- Liver Research at VBRG Liver Sinusoidal Endothelial Cell Biology