Mast cell

A mast cell is a type of white blood cell that exerts pro-inflammatory functions and serves immunoregulatory roles. Mast cells are present in all tissues and are most commonly known for their role in the mucosal immune system; however, they are necessary in maintaining physiological homeostasis and preventing pathogenesis throughout the body.

When a mast cell encounters an antigen or perceived immune threat, anti-inflammatory mediators are released through a process known as degranulation. Some anti-inflammatory mediators may include histamine, cytokines, proteases, or heparin.

Degranulation
Mast cells can become activated when their associated antibody receptors come in direct contact with an antigen. A cascade response allows for degranulation to begin and a subsequent release of anti-inflammatroy granules into the bloodstream.

Sunshine
Ultraviolet B light induced histamine release from mast cells in rats in a dose-dependent manner, and was inhibited by Vitamin C.

Inhibition
Vitamin C reduces blood histamine levels, potentially through several mechanisms: by inhibiting mast cell production; by increasing diamine oxidase (an enzyme that breaks down histamine); by inhibiting mast cell degranulation (and the release of histamine in the first place), and by inhibiting histidine decarboxylase (the enzyme that forms histamine). Vitamin B6 is also a diamine oxidase cofactor.

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.

MCAD should be distinguished from mastocytosis, a genetic disorder of excessive populations of mast cells.

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.

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)