The laboratory has been focused during the last year on immune-mediated tumor cell destruction. Natural killer (NK) cells and cytotoxic T cells (CTL) have the ability to lyse virally-infected and tumor cells. There are two proposed major mechanisms whereby they accomplish this (1) the exocytosis of lytic granules and (2) the expression of cytotoxic molecules like tumor necrosis factor (TNF) or a related molecule known as Fas-ligand. The cytolytic granules contain a variety of unique proteins, including a pore-forming protein (perforin) and a family of serine protease enzymes (granzymes). We have previously identified, sequenced and cloned 2 novel members of the granzyme family which cleaves synthetic substrates after the amino acids arginine or lysine (tryptase-2) and methionine (met-ase). We have developed specific polyclonal antisera to the met-ase and are currently trying to determine its cellular distribution in a variety of leukocyte subsets. Preliminary evidence suggests that this enzyme may be restricted in its expression to NK cells. We are also trying to define the biological role of these enzymes. In addition, we have investigated immune-mediated destruction of a murine renal cancer Renca. We found that the proinflammatory cytokines interferon gamma and tumor necrosis factor enhance Fas expression on Renca cells. Furthermore, this increased surface expression correlates with a dramatic increase in the sensivity of these cells to Fas ligand mediated apoptosis. There is synergistic interaction between the cytokines for both increases in Fas expression and susceptibility to apoptosis. We are currently investigating whether such effects play an important role in immune-mediated rejection of Renca in vivo.
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