Growth of FasL-bearing tumor cells in syngeneic murine host induces apoptosis and toxicity in Fas+ organs

Abstract

AbstractIn the current study, we investigated whether the growth of FasL-bearing tumor cells would induce apoptosis and toxicity in organs that express high level of Fas. Sera from C57BL/6 +/+(wild-type) mice injected with syngeneic FasL+ tumors, LSA, or EL-4, showed significantly higher levels of soluble FasL than that from the nontumor-bearing mice. Furthermore, the soluble FasL was functional inasmuch as the sera from tumor-bearing mice were able to induce apoptosis in Fas+ but not Fas−targets. Histopathologic studies and in situ TUNEL assay to detect apoptosis were carried out in C57BL/6 +/+(Fas+) or C57BL/6 lpr/lpr (Fas−) mice injected with syngeneic LSA and EL-4 tumor cells. The morphology of the liver and thymus from tumor bearing C57BL/6 +/+ mice showed marked damage and tissue destruction. In contrast, the liver and thymus from tumor-bearing C57BL/6 lpr/lpr mice showed minimal damage. Furthermore, the tumor-bearing C57BL/6 +/+, but not the C57BL/6 lpr/lpr, mice exhibited significant apoptosis in the liver and thymus. The FasL responsible for toxicity was tumor derived rather than host derived; tumor-bearing C57BL/6 gld/gld(FasL-defective) mice also exhibited significant apoptosis in the liver and thymus. Together, these data suggested that the in vivo growth of FasL-bearing tumor cells can induce significant apoptosis and toxicity in Fas+ tissues of the host. Such toxicity may be mediated by the soluble FasL produced by tumor cells.