B7-H1Ig treatment diminished otherwise abundant hepatocellular necrosis and apoptosis in IR-injured livers (2.3 ± 0.6 versus 38.0 ± 2.0; P < 0.001) ( Fig. 4A,B). In parallel, western blot analysis revealed selectively decreased expression (AU) of cleaved caspase-3 and increased anti-necrotic/apoptotic Bcl-2/Bcl-xl proteins

in the B7-H1Ig group (control Ig versus B7-H1Ig: 1.84 ± 0.041 versus 0.07 ± 0.020 [cleaved caspase-3], 0.20 ± 0.081 versus 2.12 ± 0.086 [Bcl-2], 0.29 ± 0.064 versus 2.08 ± 0.120 [Bcl-xl]) (Fig. 4C). As liver inflammation response to IR in B7-H1Ig–treated mice was characterized by selectively increased IL-10 ( Fig. 3C), the question of whether IL-10 played a cytoprotective function was addressed by neutralizing IL-10. Indeed, significant increase in liver injury was observed after infusion of B7-H1Ig–treated mice with anti–IL-10 mAb, as shown by sALT levels GW-572016 purchase (1,656.7 ± 358 versus 163 ±

30 U/L after B7-H1Ig monotherapy, P < 0.001) (Fig. 5A) and liver histology (Fig. 5B). Livers in B7-H1Ig–treated see more mice in which IL-10 was neutralized were characterized by zonal/panlobular parenchyma necrosis (Suzuki score 3.88 ± 0.25), which was comparable with controls (Fig. 1B). Infusion of anti–IL-10 mAb triggered a significant (P < 0.01) increase in the inflammatory gene expression programs (CXCL-10, TNF-α, and IL-6). Thus, IL-10 neutralization re-created liver IRI, rendered B7-H1Ig–treated hosts susceptible mafosfamide to IR, and confirmed the pivotal cytoprotective role of IL-10 produced by B7-H1Ig engagement. We analyzed the immunomodulatory function of PD-1/B7-H1 signaling in a well-controlled cell culture system, designed to mimic liver IRI. First, we screened anti-CD3 mAb-mediated activation of T cells with control Ig/B7-H1Ig by enzyme-linked immunosorbent

assay ( Fig. 6A). Addition of B7-H1Ig decreased IFN-γ levels (88.3 ± 21 versus 1267.8 ± 30 pg/mL, P < 0.001) yet increased IL-10 levels (641.8 ± 42 versus 302.1 ± 72 pg/mL, P < 0.05) compared with control Ig cultures. These data confirm our in vivo finding (Fig. 3) that activation of the PD-1/B7-H1 pathway preferentially induces T cell–derived IL-10. The cross-talk between T lymphocytes and macrophages is essential for the progression of liver injury in the early phase of IRI.6, 15 To address the mechanism by which B7-H1 engagement may affect macrophage priming, we cultured mouse BMMs plus anti-CD3 mAb-stimulated T cells with control Ig, B7-H1Ig, or B7-H1Ig plus anti–IL-10 mAb ( Fig. 6B). Anti-CD3–activated T lymphocytes primed BMMs in this coculture system, as evidenced by increased TNF-α/IL-6 elaboration (P < 0.01). Interestingly, B7-H1Ig suppressed macrophage-induced TNF-α and IL-6 levels (62.0 ± 6 versus 174.6 ± 11 pg/mL [TNF-α], 129.2 ± 8 versus 653.4 ± 7 pg/mL [IL-6]; P < 0.01). However, concomitant anti–IL-10 mAb re-created BMM activation, as evidenced by augmented TNF-α (123.0 ± 3 pg/mL) and IL-6 (356.5 ± 9 pg/mL) expression.