2021 Volume 33 Issue 192 Pages E27-E32
Mast cells are characterized by large, intracellular secretory granules that accumulate large amounts of glycosaminoglycans, heparin and highly sulfated chondroitin depending on the mast cell type. The granular complex, a kind of protein-polyelectrolyte complex, is composed of these glycosaminoglycans, proteases, biogenic amines, and other mediator molecules. Recent findings suggest that, after the granular complex is released, it may undergo various fates, i.e., components of the complex are either transferred into the blood flow; or they may be retained in the connective tissues near the mast cells; or ingested by epithelial, interstitial or immune cells to trigger the adaptive immune responses or to maintain tissue homeostasis; or they may be transferred to the draining lymph nodes through lymph flow. The choice of fate is greatly influenced by carbohydrates in the granular complex, especially by processed heparin via heparanase-mediated cleavage. The present review focuses on recent developments on the formation of granular complex, especially on the processing of the granular heparin, the fates and roles of the complex after being released, its potential role as an immunomodulator, and a recent attempt to mimic the complex as an artificial delivery system. The involvement of carbohydrates in these functions is also discussed.
