Selectively inducing apoptosis of activated T cells is essential for the clearance of pathogenic injurious cells and subsequent efficient resolution of inflammation. However, few chemicals have been reported to trigger apoptosis of activated T cells in the treatment of hepatitis without affecting quiescent T cells. In the present study, we found that fraxinellone, a small natural compound isolated from the root bark of Dictamnus dasycarpus, selectively facilitated apoptosis of concanavalin A (Con A)-activated CD4+ T cells rather than those non-activated, by disrupting the mitochondrial transmembrane potential, decreasing the ratio of Bcl-2/Bax, and increasing cytochrome c release from the mitochondria to the cytosol. The enhancement in Fas expression and caspase-8 activity, truncation of Bid, and down-regulation of antiapoptotic cellular FLICE-inhibitory protein expression by fraxinellone also suggested the participation of an extrinsic apoptosis pathway. Furthermore, fraxinellone significantly alleviated Con A-induced T-celldependent hepatitis in mice, which was closely associated with reduced serum transaminases, proinflammatory cytokines, and pathologic parameters. Consistent with the in vitro results, fraxinellone dramatically induced apoptosis of activated peripheral CD4+ T cells in vivo, consequently resulting in less CD4+ T-cell activation and infiltration to the liver. These results strongly suggest fraxinellone might be a potential leading compound useful in treating T-cell-mediated liver disorders in humans.

Aims: The roles of specific active ingredients in Chinese medicinal formulas have not been clearly elucidated. In this study, we selectively deleted and replenished paeoniflorin from Si-Ni-San, a traditional Chinese prescription, and aimed to identify the molecular basis of how paeoniflorin exerted its effect in Si-Ni-San. Main methods: Contact dermatitis was induced in mice with picryl chloride. Paeoniflorin was selectively deleted from Si-Ni-San by an immunoaffinity column. Quantitative real-time PCR, western blot, and enzymelinked immunosorbent assay were used in this study. Key findings: Both Si-Ni-San and paeoniflorin significantly reduced ear swelling in mice while the paeoniflorindeleted Si-Ni-San (Si-Ni-SanPF-) showed little ameliorative effect. In lipopolysaccharide-evokedmacrophages, Si-Ni-San and paeoniflorinmarkedly inhibited tumor necrosis factor-αproduction, cyclooxygenase-2 activity, aswell as extracellular signal-regulated kinase 1/2 phosphorylation while Si-Ni-SanPF-exhibited no or slight inhibitory effect. Furthermore, the inhibitory effect on the production of tumor necrosis factor-α reappeared when different proportions of paeoniflorinwere replenished in Si-Ni-SanPF-. In addition, the expression ofmacrophagemigration inhibitory factor in T cells, rather thanmacrophages,was significantly inhibited by Si-Ni-San, but not Si-Ni-SanPF-.Ourdata indicate paeoniflorin is the principal component of Si-Ni-San, exertingnegative regulationon the function of macrophages in contact dermatitis. Significance: The present study suggests that dissecting the role of specific constituents in medicinal formulas through selective deletion and replenishment may be a useful strategy in recognizing and validating an active ingredient in traditional Chinese medicine.

Regulation of signal transducer and activator of transcription (STAT) 1 signaling is being explored as a new approach to the treatment of inflammatory bowel diseases. However, few chemicals have been reported to inhibit IFN-g/STAT1 signaling for Crohn's disease therapy. In the present study, we found that cirsilineol, a small natural compound isolated from Artemisia vestita, significantly ameliorated trinitro-benzene sulfonic acid (TNBS)-induced T-cell-mediated experimental colitis in mice, which was closely associated with reduced autoreactive T-cell proliferation and activation. Moreover, the regulatory action of pro-inflammatory and anti-inflammatory cytokine by cirsilineol treatment was found to decrease the activity of effector Th1 cells but increase the activity of regulatory T cells as characterized by down-regulation of IFN-g and corresponding up-regulation of IL-10 and TGF-b. The therapeutic effect of cirsilineol was attributable to a novel regulatory mechanism with selective inhibiting IFN-g signaling in colonic lamina propria CD4+ T cells, which was mediated through downregulating STAT1 activation and T-bet expression. Furthermore, cirsilineol was found to down-regulate the activation of JAK2, a critical kinase for IFN-g/STAT1 signaling, and abrogate the expression of T-bet, resulting in markedly decreased proliferation and activation of T cells in vitro. Importantly, the inhibition of IFN-g/STAT1 signaling by cirsilineol was reversible in the presence of high level of IFN-g. These results strongly suggest that cirsilineol might be potentially useful for treating T-cell-mediated human inflammatory bowel diseases.

In the present study, we aimed at examining the immunosuppressive activity of saikosaponin a, a triterpene saponin derived from Bupleurum falcatum L. (Umbelliferae), and the underlying mechanisms. Saikosaponin a significantly inhibited the proliferation and activation of T cells activated by concanavalin A (Con A) in a concentration-dependent manner. Additionally, it potently suppressed Con A-stimulated IL-2, IFN-γ and TNF-α production inmouse Tcells. Saikosaponin a also causedG0/G1 arrest of activated Tcells through down-regulating the protein levels of CDK6 and Cyclin D3 and up-regulating the protein level of p27kip. Furthermore, the compound dose-dependently induced apoptosis of Con A-activated T cells rather than those non-activated, as determined by Annexin V/PI staining. Besides, it induced a remarkable collapse of mitochondrial membrane potential and caused significant release of cytochrome c from mitochondria to cytosol. In summary, these results suggest that the G0/G1 arrest aswell as the induction of apoptosis viamitochondrial pathway are involved in the immunosuppressive activity of saikosaponin a against activated T cells. This may herald a novel approach for further studies of saikosaponin a as a candidate for the treatment of inflammatory and autoimmune diseases.