Biological complexity: immune cell stem cell cooperation (Introduction)

by David Turell , Friday, July 08, 2016, 15:21 (2846 days ago) @ David Turell

How the body is developed and maintained is slowly being understood. As the body cell population is turned over at a rather high rate stem cells and the various immune cells are programmed to work together"-http://www.the-scientist.com/?articles.view/articleNo/46377/title/Immune-Cell-Stem-Cell-Cooperation/-"We may perceive ourselves as static beings, but the cells of our bodies are in constant flux. The outer layers of our skin and intestinal tract are replaced every few weeks; red blood cells circulate in our bodies for about 100 days before they are replaced; cells in our liver and fat are longer lived—more than a year for a liver cell, 10 years on average for a fat cell—but still turn over repeatedly during our lifetimes. More slowly, up to half our heart cells may be replaced during a normal lifespan. And, of course, when healthy tissue is lost due to injury, new cells are made to patch up the damage. -***-"Stem cells self-renew to maintain their numbers and differentiate into the specialized cell types that make up our tissues and organs—a function that becomes especially important after stress or injury. -***-"One of the best-studied examples of mammalian stem cell environments is the intestinal stem cell (ISC) niche. The small intestine's epithelium is the fastest self-renewing tissue in the body due to ISCs' exceptionally rapid rates of cell division and the rapid migration of their differentiated progeny out of the stem cell niche. But the system would not work without the help of Paneth cells, one of four differentiated cell types produced by ISCs, which remain in the niche and secrete essential proteins that are critical for ISC survival. Indeed, the genetic inactivation of Paneth cells results in a near-total loss of ISCs.-***-"An integral part of homeostasis in diverse tissues is the continuous replacement of differentiated cell types. Research is now showing that the immune cells residing within the stem cell niche are essential to this process. For example, specialized macrophages in the bone marrow remain in direct contact with a red blood stem cell called an erythroblast.-***-"At the start of puberty, ovarian hormones trigger the bifurcation and elongation of the ductal structures towards the outer edges of the fat pad while diverse immune cells—mast cells, eosinophils, and macrophages—migrate to the region around the ducts' tips. Genetic or pharmacological disruption of mast cells and macrophages in mice has revealed that these immune cells are critical for rapid proliferation and normal duct branching during puberty. Mast cells secrete protein-degrading serine proteases, which are necessary for the breakdown and reorganization of collagen fibers surrounding the developing ducts, for example,3 while macrophages phagocytize apoptotic cell debris and directly act on mammary stem cells through an unknown mechanism.-***-"Perhaps the best-understood example of immune- and stem-cell cooperation is in skeletal muscle following an acute injury. Tissue repair begins with the removal of damaged muscle fibers by local and infiltrating immune cells. Rare, circulating immune cells called eosinophils instruct resident progenitor cells known as fibro/adipogenic progenitors (FAPs) to generate the fibroblasts and fat cells that deposit collagen and secrete growth factors to support muscle fiber regeneration.8 Concurrently, T cells secrete a protein called amphiregulin, which instructs resident muscle stem cells known as satellite cells to differentiate into new muscle cells and replace the lost muscle fibers.-***-"When researchers plucked hairs off the backs of mice, they found that damaged hair follicles beneath the skin's surface secrete, in unison, a protein called CCL2. In response to this distress signal, macrophages migrated up the CCL2 gradient and toward hair follicles, where they secreted a protein called tumor necrosis factor (TNF), which instructed hair follicle stem cells to produce new hair.-***-"Tissue-resident stem cells' remarkable ability to self-renew while also giving rise to diverse mature cell types is critical for our existence. In order to carry out their inherent roles in tissue maintenance and regeneration, these stem cells rely on signals provided by diverse cell types, including immune cells, within the local and systemic environments. We are at the dawn of understanding the complex and dynamic roles of the immune system's many cell types and their functional relationships with stem cells—a feat that will be critical to harnessing the power of stem cells to treat or cure disease."-Comment: The complex automated dance between cells to maintain the body is illustrated by the bits of tis article I've reproduced. I've skipped the part on uses in regenerative medicine. This complexity tells me only an intelligent mind could create these mechanisms. Each cell works with purpose, programmed purpose, exhibiting intelligent activity. It is programmed intelligence guiding each cell.