Effect of IL-15 on APAP Hepatitis Figure 6. The induction of hepatic reactive nitrogen species (RNS) is greater in Il152/2 than WT mice with APAP challenge. (A) Immunohistochemistry of iNOS expression, (B) nitrotyrosine formation and (C) percentage of iNOS or nitrotyrosine-positive area at 0, 2, 4 and 8 hr after APAP challenge. *P,0.05; **P,0.01. Data are mean 6 SEM from 3 mice per group. doi:10.1371/journal.pone.0044880.g006 ALT levels at 8 hr post-APAP (Figure 10A). Similarly, vinblastine could not change the sensitivity to APAP hepatitis in WT mice (Figure 10A). The role of KCs in APAP hepatotoxicity still remained controversial [41], therefore we further evaluated the role of KCs in our model. A low dose of GdCl3 (7 mg/kg) was reported to inactivate KCs and modestly reduced APAP hepatitis [11], whereas the high dose of GdCl3 (30 mg/kg) has been reported to eliminate KCs in mice, thereby abrogating cadmium (Cd) induced hepatotoxicity [42]. Therefore, 30 mg/kg of GdCl3, a dose eliminating KCs by Indian ink uptake assay (data not shown) without liver damage, was used in our further studies. The KC-eliminated WT mice, by GdCl3, showed an increased susceptibility to APAP (Figure 10B,D), indicating a protective role of KCs in AILI and the accompanied inflammation (Figure 10E,F). This finding was compatible with previous protective role of KCs in AILI by Ju et al. in C57BL/6J WT mice [11]. Moreover, GdCl3 pre-treatment significantly reduced serum IL-15 elevation of WT mice during AILI (Figure 10C,D). Thus, KCs were probably the dominant IL-15 producer in APAP hepatitis. Since mice lack of KCs shared similar sensitivity to APAP hepatotoxicity with mice deficiency of IL-15 (Figure 10B), it implicated a regulatory correlation between IL-15 and KCs in AILI. Furthermore, elimination of KCs in Il152/2 mice did not affect the AILI severity (Figure 10B), hepatic TNFa and IL-1b (Figure 10E), as well as liver nitrotyrosine formation (Figure 10F), inferring a potential role of IL-15 in mediating KC effect on AILI. Further study is needed to clarify this assumption. Discussion Use of genetically knockout mice is a novel strategy to elucidate the role of IL-15 in AILI. However, a recent report demonstrated PLOS ONE | www.plosone.org 8 September 2012 | Volume 7 | Issue 9 | e44880