FasL-dependent elevation of serum IL-18 levels after induction of aGVHD.

(A) Elevation of IL-18 serum levels after induction of aGVHD. BDF1 mice were lethally irradiated and underwent transplantation with 5 × 10⁷ spleen cells from BDF1 (Syn, ■) or WT B6 (aGVHD, ●) mice. At the indicated day, the serum was sampled for measurement of IL-18 concentration by ELISA. Data represent the mean ± SD of 5 mice in each experimental group. *P < .0001 by Fisher PLSD test. Similar results were obtained in 3 independent experiments. (B) Lack of increase in serum levels of IL-18 in the recipients engrafted with gld/gldspleen cells. Lethally irradiated BDF1 mice had transplantation with 5 × 10⁷ spleen cells from BDF1 mice (Syn), WT B6 mice (aGVHD), or gld/gld B6 mice (gld/gld). At day 10, serum levels of IL-18 were measured by ELISA. Data represent the mean ± SD of 5 mice in each experimental group. Similar results were obtained in 3 independent experiments. (C) Fas/FasL-dependent IL-18 secretion in vitro by Kupffer cells from aGVHD hosts. Kupffer cells were prepared from BDF1 mice having transplantation with BDF1 spleen cells (Syn; ■ A,C,E,G) or WT B6 cells (aGVHD; ▪ B,D,F,H) at day 7, and were incubated with 1 μg/mL LPS or mFasL in the presence or absence of neutralizing anti–murine FasL (αFasL) mAb for 24 hours. The IL-18 concentration in each supernatant was measured by ELISA. Control hamster IgG did not down-regulate the secretion of IL-18 from Kupffer cells from hosts having transplantation with BDF1 or WT B6 cells upon stimulation with mFasL. Data are presented as mean ± SD of triplicate cultures. Similar results were obtained in 3 independent experiments. ND indicates not detectable; NS, not significant.