Structure and Possible Functions of Lymphocyte Granzymes

The participation of cellular serine proteinases in many physiological processes has been widely documented. These enzymes are most active at neutral, i.e., physiological pH. A number of studies have suggested that they may be involved in cellular chemotaxis, protein turnover in tissues, endocytosis and exocytosis, peptide hormone processing, cellular invasiveness or tumorigenesis, and cell proliferation (for reviews, see Mullins and Rohrlich, 1983; Neurath, 1984). These suggestions were based on the interference of proteinase inhibitors with cellular function or proliferation and the detection of cell-associated esterolytic, amidolytic, or proteolytic activities, notably in hemopoietic cells of the immune defense system, including lymphocytes, natural killer (NK) cells, mast cells, and phagocytes. This review will focus on a subfamily of serine proteases expressed in granules of lymphocytes and NK cells.