Mast cell

Mast cells (mastocytes) are cells of the body's own defence system that have stored messenger substances, including histamine and heparin. They are 20-30 µm in size.

Paul Ehrlich discovered them and called them "mast cells", probably because he wrongly assumed that the cells had the ability to phagocytose. However, the granules stored in it are produced by the cell itself. Another version says that Ehrlich assumed that these cells use their fatty granules to feed or "fatten" surrounding cells.

The basophilic granulocytes, sometimes also called blood mast cells, differ from the actual mast cells. The latter are found throughout the body in the interstitial connective tissue, but most frequently in the submucosa of the intestine and respiratory tract and in the dermis (corium), near vessels and nerves.

The mast cell plays an important role in type 1 allergy (IgE-mediated allergies such as asthma, allergic rhinitis, systemic anaphylaxis): Upon first contact with an allergen, the affected person initially remains completely asymptomatic, but the production of specific IgE antibodies is triggered by plasma cells directed against the specific allergen. The mass-produced IgE antibodies attach themselves with the foot part (Fc part = fragment crystallizable) to the surface of mast cells, which are found everywhere in the body, especially in the mucous membranes, and sensitize them to the reaction to the allergen. The allergic reaction does not occur until the second contact with the allergen, when the allergens bind to each of two adjacent IgE antibodies on the mast cells, causing them to cross-link. This stimulates the mast cells to empty their granules in the process of exocytosis and to release the histamine contained therein (degranulation). Histamine is a messenger substance that binds to receptors of the surrounding tissue cells and causes violent effects within a few seconds. This process is called an immediate allergic reaction (immune response) because allergic symptoms occur within seconds to minutes. The rapid onset of symptoms is due to the immediate reaction of the surrounding tissue to the secreted substances: Vessels dilate, fluid is deposited (wheal formation), etc. The numerous mast cells positioned near the vessels are actively waiting for IgE.

There is also a non-immunological degranulation of mast cells. This means that a release reaction (as described in the above paragraph) also takes place, i.e. histamine, heparin and other mediators are released by mast cells, but this without the involvement of antibodies. Certain molecular structures, e.g. of drugs, are able to trigger the non-immunological mast cell degranulation.

With age, the number of mast cells increases, it is therefore assumed that mast cells and their constituents contribute to the aging process. In addition to the above-mentioned role in triggering allergic symptoms, the mast cell is also of central importance in other diseases such as urticaria and mastocytosis. The physiological functions of mast cells are mainly in the defense against bacteria and parasites as well as in the protection against animal toxins.