What Are Mast Cells?
In 1878, medical student Paul Ehrlich, who was later to be awarded the Nobel Prize, discovered numerous cells filled with granules under the light microscope using new staining methods. Because they looked well-fed to him, Ehrlich named these cells “Mastzellen” (from German ”Mast”– fattening, feeding).
It was not until a century later that scientists found out that mast cells in tissues arise from stem cells in the bone marrow and, therefore, are cells of the immune system.
Mast cells are found in lower invertebrates as well as vertebrates, suggesting that they serve a fundamental role within the immune system. We now believe these may have been some of our first lines of defense to evolve against the toxins in our environment.
Mast cells are ubiquitous throughout the tissues of the human body and play numerous roles, both beneficial and destructive. We know they are important in our army of immunity warrior cells, which defend us against viruses, bacteria and parasitic invaders.
They are also very well known for the havoc they wreak, causing uncomfortable symptoms due to their release of histamine and other mediators which cause the all too familiar itching, sneezing, urticaria and rhinorrhea of allergic responses.
Mast cell activities are diverse and include painful inflammatory reactions in autoimmune conditions such as rheumatoid arthritis. In the gastrointestinal system, mast cells are implicated in diverse actions such as increased gastric acid secretion, polyp formation and uncomfortable conditions such as Irritable Bowel Syndrome.
Mast cells have long been recognized for their participation in allergic disease, including asthma, rhinitis, conjunctivitis, atopic dermatitis, urticaria, and anaphylaxis. However, they also have a variety of protective and regenerative roles throughout the body
Mast cells have been noted for many years to be present within human atherosclerotic lesions although their function within these lesions is unclear .
Mast cells are white blood cells which originate in the bone marrow, where they only spend around 4 days. They comprise a very small proportion of the marrow cells. They leave the bone marrow in a relatively immature state. They circulate only briefly in the blood vessels. They rapidly leave the circulation and enter the peripheral tissues, where they mature. They are present in every peripheral tissue in the body, where they are relatively immobile and tend to live as long as the patient lives.
Mast cells are found in varying quantities in virtually all tissues of the human body and are stationed much like sentinel cells of the immune system at bodily portals of entry. The numbers of mast cells are highest at locations where they can respond to foreign organisms and antigens, thereby concentrating heavily in the skin, intestines, the inside of the eyelids, lungs and airways.
They are even present in the atrial appendage of the heart. Mast cells are also found in the brain, and in low numbers in the kidneys and bone marrow. They are often located closely to blood vessels, nerves and lymphatics.
A unique feature of mast cells is that they do not die after degranulation. In some circumstances, some of the cells withstand the exhaustive degranulation process, survive, are reloaded with new granules, and during the next few weeks can be activated again. These are long lived cells that are hard to kill.
Mast cell numbers increase significantly at multiple areas in mastocytosis.
From their vantage point surrounding blood vessels, their actions can influence the function of vascular structures, monitor blood for inflammatory and infectious changes and distribute mediators, which they release in response to a specific stimulus.
In addition, it has long been appreciated that there are tissue-specific differences in mast cells. Therefore, the specific contribution of a mast cell may depend on its location and the location of the nearby target cells, the type of the activating signals it receives, the intensity of the signals and the genetic background of the individual.