We report here that the progression of pancreatic carcinomas in tumor patients is associated with increased serum levels of both the soluble forms of CD95 ligand (CD95L/FasL) and its receptor, CD95 (Fas). Shedding of proteolytically processed soluble CD95L was also observed in pancreatic carcinoma cells in vitro, thus identifying one possible source of CD95L in patients' sera. Because the secreted forms of both CD95 and CD95L have been implicated previously in protection of cells from CD95-mediated cell death, we assessed the effect of soluble CD95L in supernatants of pancreatic carcinoma cells on viability of Jurkat T lymphocytes. We describe that (a) supernatants derived from cultured pancreatic carcinoma cells caused apoptosis of Jurkat cells; (b) soluble tumor-derived CD95L contributed significantly to this effect; and (c) in comparison to Jurkat cells, pancreatic carcinoma cells themselves revealed increased resistance to apoptosis induction by autocrine soluble CD95L. These results are consistent with the notion that in the microenvironment of pancreatic tumors, tumor-derived shed CD95L exerts paracrine pro-apoptotic effects. In addition, because it is released at high levels into the bloodstream, soluble CD95L may have systemic effects in tumor patients that reach beyond the microenvironment of the tumor site.
