Lymphatic Endothelium
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The lymphatic endothelium refers to a specialized subset of
endothelial cells The endothelium (: endothelia) is a single layer of squamous endothelial cells that line the interior surface of blood vessels and lymphatic vessels. The endothelium forms an interface between circulating blood or lymph in the lumen and the res ...
located in the sinus systems of draining
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 ...
. Specifically, these endothelial cells line the branched sinus systems formed by afferent lymphatic vessels, forming a single-cell layer which functions in a variety of critical physiological processes. These lymphatic endothelial cells contribute directly to immune function and response modulation, provide transport selectivity, and demonstrate orchestration of bidirectional signaling cascades. Additionally, lymphatic endothelial cells may be implicated in downstream immune cell development as well as lymphatic organogenesis. (Jalkanen, S., Salmi, M. 2020) Until recently, lymphatic endothelial cells have not been characterized to their optimal potential. This system is very important in the function of continuous removal of
interstitial fluid In cell biology, extracellular fluid (ECF) denotes all body fluid outside the Cell (biology), cells of any multicellular organism. Body water, Total body water in healthy adults is about 50–60% (range 45 to 75%) of total body weight; women ...
and proteins, while also having a significant function of entry for
leukocytes White blood cells (scientific name leukocytes), also called immune cells or immunocytes, are cells of the immune system that are involved in protecting the body against both infectious disease and foreign entities. White blood cells are genera ...
and tumor cells. This leads to further research that is being developed on the relationship between lymphatic endothelium and metastasis of tumor cells (Pepper, M. S., & Skobe, M. 27 October 2003). The lymphatic capillaries are described to be blind ended vessels (closed on one end), and they are made up of a single non-fenestrated layer of endothelial cells; The lymph capillaries function to aid in the uptake of fluids, macromolecules, and cells. Although they are generally similar to blood capillaries, the lymph capillaries have distinct structural differences. Lymph capillaries consist of a more wide and irregular lumen, and the endothelium in lymph capillaries is much thinner as well (S. Pepper, Skobe 2003). Their origin has been speculated to vary based on them being dependent on specific tissue environments, and powered by organ-specific signals.(L. Gutierrez-Miranda, K. Yaniv, 2020). A
lymph Lymph () is the fluid that flows through the lymphatic system, a system composed of lymph vessels (channels) and intervening lymph nodes whose function, like the venous system, is to return fluid from the tissues to be recirculated. At the ori ...
capillary endothelial cell is distinct from other endothelial cells in that
collagen fiber Type I collagen is the most abundant collagen of the human body, consisting of around 90% of the body's total collagen in vertebrates. Due to this, it is also the most abundant protein type found in all vertebrates. Type I forms large, eosinop ...
s are directly attached to its
plasma membrane The cell membrane (also known as the plasma membrane or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the interior of a cell from the outside environment (the extr ...
. Although lymphatics were first described by
Hippocrates Hippocrates of Kos (; ; ), also known as Hippocrates II, was a Greek physician and philosopher of the Classical Greece, classical period who is considered one of the most outstanding figures in the history of medicine. He is traditionally referr ...
in 400 BC and rediscovered as "milky veins in the gut of a well fed dog" in the 17th century by Gasparo Aselli, they were ignored for centuries until in 1937
Howard Florey Howard Walter Florey, Baron Florey, (; 24 September 1898 – 21 February 1968) was an Australian pharmacologist and pathologist who shared the Nobel Prize in Physiology or Medicine in 1945 with Ernst Chain and Sir Alexander Fleming for his ro ...
showed that lymphatics enlarge in inflammation. At this stage vascular and lymphatic endothelia were seen to be morphologically distinct and lymphatic vessels considered less important. Later it was discovered that VEGF-R3 and
VEGF-C Vascular endothelial growth factor C (VEGF-C) is a protein that is a member of the platelet-derived growth factor / vascular endothelial growth factor (PDGF/VEGF) family. It is encoded in humans by the ''VEGFC'' gene, which is located on chromosom ...
/
VEGF-D C-fos-induced growth factor (FIGF) (or vascular endothelial growth factor D, VEGF-D) is a vascular endothelial growth factor that in humans is encoded by the ''FIGF'' gene In biology, the word gene has two meanings. The Mendelian gene is a ...
were the key growth factors controlling lymphatic endothelial proliferation. Markers of lymphatic endolthelium were not discovered until relatively recently. These being LYVE-1 (Jackson et al., 1999) and
podoplanin PDPN, i.e., podoplanin is a small glycoprotein located on the surface membranes of various cell types. While termed PDPN in humans, it is often named: a) OTS-8, gp38, aggrus, antigen PA2.26, or RANDAM-2 (i.e., retinoic acid-induced neuronal diff ...
(Kerjaschki, 1999).


See also

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Lymphatic system The lymphatic system, or lymphoid system, is an organ system in vertebrates that is part of the immune system and complementary to the circulatory system. It consists of a large network of lymphatic vessels, lymph nodes, lymphoid organs, lympha ...
*
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 ...


References


Further reading

* * * * * * * * * * * * * * * * {{refend Lymphatic system Lymphatic tissue