List of abbreviations
of micros-
specialist terms
explained in
English +

Every attempt was made to provide correct information and labelling, however any liability for eventual errors or incompleteness is rejected!

dieser Seite

Dr. med.
H. Jastrow

of use
Overview mast cells (Mastocyti):
Pages with explanations are linked to the text below the images if available!
human mast cell (type 1)
from subcutis
left detail thereof 1 right detail thereof 2 human mast cell
(type 1)
human mast cell (type 1) from the sclera of
the eye-bulb (4 hrs post mortem fixed)
human mast cell
vesicles 1
human mast cell
(Type 1)
human mast cell
vesicles 2
human mast cell
vesicles 3
human mast cell
vesicles 4
human mast cell
vesicles 5
human mast cell
(type 1)
human mast cell vesicles some of
which are in state of regeneration
human mast cell
(type 2)
detail: human mast
cell vesicles 6
detail: human mast
cell vesicles 7
human mast cell vesicles 8
from a further mast cell
rat mast cell 1
anterior detail thereof posterior detail thereof rat mast cell vesicles 1 rat mast cell vesicles 2
rat mast cell vesicles 3 and an
undamaged extracellular vesicle
rat mast cell
vesicles 4
univacuolar fat cell
+ rat mast cell 2
previous mast cell of the rat in detail mast cells of rat 3
A mast cell (Mastocyte; Termionologia histologica: Mastocytus) is a free cell of the connective tissue. According to their location mast cells on their most frequent places have a special terminology: either as mucosa related mast cells (Termionologia histologica: Mastocyti mucosales) or as perivascular mast cells (Termionologia histologica: Mastocyti perivasculares). Mast cells are actively mobile, i.e. they are able to migrate through surrounding extracellular matrix using their pseudopods (or filopods) which are several micrometers long and motile. The mast cell cytoplasm contains several hundred vesicles (NO  granules!). Stimulation by Immunglobulin E (IgE) effects on one hand an exocytosis: vesicle fusion with the cell membrane and release of vesicle content on the other hand some intact vesicles (with membrane) leave the cell (image on the lower left). Fast release of vesicle content is of major imoprtance in allergic reaction of the immediate type (Type 1 allergy). After a necessary first contact with the antigen specific IgE antibodies are produced by plasma cells, these IgEs bind on mast cells that then begin to produce an FceRI receptor which is expressed on the cell membrane. In case of new presence of the antigene the latter binds to the FceRI receptor of the sensitized mast cell and causes the allergic reaction proviously mentioned. This immediate release of mast cell vesicle content has been calledcompound exocytosis. The expression mast cell degranulation meaning the same is based on early light microscopy and is not correct since infact it is a fast exocytosis of vesicles characterized by a surrounding membrane. Accordingly, the established term mast cell granule is not correct since a true granule like e.g., a Glycogen granule is not surrounded by a membrane. As can be seen in the images, mast cell vesicles of the rat are very electron-dense and homogenous. In Man different kinds of vesicles are encountered. The maximal diameter of the vesicles is about 1 µm. They are basophilic, water soluble and metachromatic in some light microscopic stains. Chemically the vesicles contain water, histamin, heparin and glykosaminoglycans (consisting of glucoronic acid, glucosamin and sulphuric acid, explaining metachromasy), chemotactic factors, tryptase and/or chymase. In rodents like rat further serotonin. Further, mast cells release mediators, of which in vesicles are stored: tumor-necrosis faktor alpha (TNFa), interleukin 4,5,6 and 8 (IL4, IL5, IL6,IL8) as well as eosinophil chemotactic factor stimulating immigration of eosinophilic granulocytes which then bloc histamine effects and help in limiting an inflammation. In addition the mast cell vesicles contain bFGF, stem cell factor, endothelial permeability factor and vascular endothelial growth factor. Further mediators are newly synthetised in mast cells only when stimulated and immediately released. Therefore they are probably not stored in the vesicles: prostaglandin GD2 (PGD2), Leukotrien C4 (LTC4), Leukotrien D4 (LTD4), platelet activating factor (PAF).
Electron microscopic aspect of mast cell vesicles: there are different components in human cylindrical membrane scrolls (see image of mast cell vesicles 6), crystals (notable on the regular striping; see image of mast cell vesicles 2,3,5,7). Some authors even clain the presence of ribosomes inside mast cell vesicles.
Usually 7,000 to 10,000 mast cells are present in 1 mm³ of the skin mostly close to capillaries, lymph vessels and nerves. Human mast cells are usually elongated cells about 5 x 15 µm in size. They derive from a multipotent stem cell in bone marrow that expresses on its surface, i.e. on the cell membrane a CD34 receptor. These stem cells may also develop into basophilic granulocytes. The direct precursors of the mast cells have no vesicles and look like monocytes. They are distributed by the blood and emerge into connective tissue on any location. Some hours later they develop fist vesicles and become mature mast cells. Basing on morphology and immunhistochemistry 3 types of mast cells are distinguished:
Type 1 most common, predominant in skin, mainly contain vesicles with amorphic electron dense content. In some cases scroll-like electron dense structures are located at the side of a partly cristalloid vesicle core (detail images 1-5). This type of mast cells synthetises tryptase and chymase.
Type 2 less common, predominant in lung, show mainly vesicles with scroll-like content and osmiophilic lipid droplets of varying electron density (detail images 6-8). The lipid bodies contain cyclooxygenase. The mast cells of type 2 only contain tryptase.
Type 3 these postulated rare type only synthetises chymase. It shall be present in axillary lymph nodes, the lung and in intestinal connective tissue.
Mast cells show only small amounts of rough endoplasmic reticulum and small Golgi fields. Besides the vesicles their cytoplasm contains some free ribosomes, microtubules, actin- and intermediate filaments. Lipid bodies are only present in type 2 mast cells. Besides the fast IgE stimulated exocytosis of vesicles, those may also be released much slower by other substances; this procedure is termed peacemeal degranulation. Mast cells are involved in allergy, acute and chronic inflammation processes, T-cell activation and tissue defense of parasites. Their function is improper in many deseases of the skin e.g., psoriasis, chronic eczema, sclerodermia, lichen simplex and - planus.

--> connective tissue, free cells in connective tissue, plasma cells, lymphocytes, blood cells, basophilic granulocytes, bone marrow
--> Electron microscopic atlas Overview
--> Homepage of the workshop

Images, page & copyright H. Jastrow.