|Budget Amount *help
¥2,700,000 (Direct Cost : ¥2,700,000)
Fiscal Year 1998 : ¥900,000 (Direct Cost : ¥900,000)
Fiscal Year 1997 : ¥1,800,000 (Direct Cost : ¥1,800,000)
Sequential administration of Propionibacterium acnes (P.acnes) and LPS induces liver injury in C57/BL6, BALB/c and BALB/c nu/nu (nude) mice. This hepatic injury model consists of two phases, priming and effector. During the priming phase, P.acnes-elicited Kupffer cells produce IL-12, that shifts hepatic T cells to type 1 cells that produce IFN-gamma. IL-12 also activates hepatic NK cells. During effector phase, P.acnes-primed and LPS-elicited Kupffer cells promptly produce TNF-alpha, IL-12 and IL-18. IL-12 and IL-18 activate hepatic lymphocytes to produce IFN-gamma, which in turn additionally activate Kupffer cells to produce more amount of TNF-alpha, a potent death factor. IL-18 also induces expression of functional Fas ligand, a second death factor, on hepatic lymphocytes. Since hepatocytes constitutively express Fas, induction of functional Fas lignad on hepatic lymphocytes directly leads to death of hepatocytes. Thus, we assume that during the priming phase with P.acnes. IL-12 is a
key molecule that induces Th1 dominant condition and during the effector phase with LPS.IL-18 induces death factors to lead to liver injury.
Thus, we investigated whether IL-12 replaces P.acnes and IL-18 replaces LPS.When lL-12 was administered instead of P.acnes, a challenge with either LPS, IL-12, IL-18 or IL-12 plus IL-18 did not induce liver injury. In contrast, either treatment induced liver injury in the mice that had been primed with P.acnes.
Next, we identified the cell type that expresses FasL and characterized the role of FasL-expressing cells in induction of this liver injury in BALB/c nu/nu (nude) mice. In the hepatic lesion, apoptotic hepatocytes were closely apposed to NK cells. Hepatic lymphocytes from nude mice included NK cells and T cells. Only hepatic NK cells expressed FasL after LPS challenge. NK cell depletion rendered the mice resistant to this liver injury in association with impaired induction of FasL.We investigated whether cloned hepatic NK cells from P.acnes-primed nude mice increase FasL expression and show hepatotoxicity in response to IL-18. IL-18 enhanced surface FasL expression on cloned hepatic NK cells, which was responsible for apoptosis-inducing activity against hepatocytes in vitro. Furthermore, adoptive transfer of IL-18-stimulated cloned hepatic NK cells induced liver injury in the P.acnes-primed nude mice, whereas transfer of those additionally treated with anti-FasL mAb failed. These results suggest that the liver injury is caused by hepatic NK cells that express FasL in response to IL-18 after LPS challenge in nude mice. Less