Mast cell

A mast cell is a type of white blood cell called a granulocyte. Mast cells are present in the conective tissues surrounding blood vessels and nerves, as well as at the barriers between the body's internal environment and the external one, including thelungs, digestive tract, nose, mouth and skin. They play an important role in the mucosal immune system and allergic response, as well as immune tolerance, defense against pathogens, and blood–brain barrier function.

When mast cells degranulate, they release histamine and heparin, an anticoagulant. Histamine causes endothelial cells lining blood vessels and lymphatic vessels to contract, weakening the junctions between these cells, and allowing proteins and cells from the plasma to leak through into the connective tissue. (CITE: http://histology.leeds.ac.uk/tissue_types/connective/connective_phagocytes.php)

Degranulation
Mast cells are activated by a transient rise in calcium in the cytosol.

Infection
In a mouse model of myocarditis, Coxsackievirus infection was found to upregulate Toll-like receptor 4 on mast cells and macrophages immediately following infection. It also increased numbers of mast cells.

Nervous system
Mast cells play an important role in the gut-brain axis of the peripheral nervous system. They are found throughout the gastrointestinal tract near sensory nerve fibers, such as the sensory vagus nerve. In the central nervous system, they are found on the blood-brain barrier, in the dural layer of the meninges, and in areas of the brain responsible for pain or neuroendocrine functions including the pituitary stalk, pineal gland, thalamus, and hypothalamus.

They are a primary type of effector cell though which intestinal pathogens can affect the brain.

Mast cell activation disorder
See full article: Mast cell activation disorder

Mast cell activation disorder (MCAD) is a disorder where mast cells are normal in number but over-responsive to dietary and environmental triggers. Cells release excess histamine and other signaling molecules, causing symptoms. It is often found in patients with Ehlers-Danlos syndrome (EDS) and postural orthostatic tachycardia syndrome (POTS), a form of orthostatic intolerance, two conditions commonly co-morbid with ME/CFS. The overlap between EDS, POTS, and MCAD is thought to be due to increased tryptase production owing to an extra copy of a gene called TPSAB1.

Chronic fatigue syndrome
One study found that moderate and severe ME/CFS patients had higher levels of naive mast cells than healthy controls. Clinicians increasingly believe that mast cells underly the dysfunction found in the disease. (cite: https://www.medscape.com/viewarticle/893858)

Mastocytosis
Mastocytosis is a genetic disorder of excessive populations of mast cells.

Notable studies

 * 2016, Novel characterisation of mast cell phenotypes from peripheral blood mononuclear cells in chronic fatigue syndrome/myalgic encephalomyelitis patients (Donald Staines, Sonya Marshall-Gradisnik)