Mast Cell - Origin and Classification

Origin and Classification

Mast cells were first described by Paul Ehrlich in his 1878 doctoral thesis on the basis of their unique staining characteristics and large granules. These granules also led him to the mistaken belief that they existed to nourish the surrounding tissue, and he named them "Mastzellen" (from the German: Mast, "fattening" as of animals). They are now considered to be part of the immune system.

Mast cells are very similar to basophil granulocytes (a class of white blood cells) in blood. Both are granulated cells that contain histamine and heparin, an anticoagulant. Both cells also release histamine upon binding to immunoglobulin E. These similarities have led many to speculate that mast cells are basophils that have "homed in" on tissues. Furthermore they share a common precursor in bone marrow. Nevertheless, both mast cells and basophils are thought to originate from bone marrow precursors expressing the CD34 molecule. Basophils leave the bone marrow already mature, whereas the mast cell circulates in an immature form, only maturing once in a tissue site. The site an immature mast cell settles in probably determines its precise characteristics.

Two types of mast cells are recognized, those from connective tissue and a distinct set of mucosal mast cells. The activities of the latter are dependent on T-cells.

Mast cells are present in most tissues characteristically surrounding blood vessels and nerves, and are especially prominent near the boundaries between the outside world and the internal milieu, such as the skin, mucosa of the lungs and digestive tract, as well as in the mouth, conjunctiva and nose.