ABSTRACT
Serglycin proteoglycans (PGs) are localized in the secretory granules of mast cells (MCs), natural killer cells, cytotoxic T lymphocytes, monocytes, macrophages, basophils, eosinophils, neutrophils, and platelets. These PGs are characterized by their uniquely protease-resistant, Ser and Gly rich protein cores and by their covalently attached, highly sulfated glycosaminoglycans (GAGs). The most negatively charged GAGs in the body are often bound to serglycin PGs, and these intracellular PGs appear to play an essential role in the packaging of positively charged proteases and other biologically active proteins in specific molar ratios in the granules of various immune cells. Because the gene that encodes the protein core of serglycin PGs is expressed early during the differentiation of hematopoietic cells and because serglycin PGs interact with so many granule constituents, the regulation of this particular gene and the modification of its translated protein core appear to be extremely important in cellular immunity.
