Triptolide impairs dendritic cell migration by inhibiting CCR7 and COX-2 expression through PI3-K/Akt and NF-kappaB pathways.

Inhibition of dendritic cell (DC) migration into tissues and secondary lymphoid organs is an efficient way to induce immunosuppression and tolerance. CCR7 and PGE(2) are critical for DC migration to secondary lymphoid organs where DC initiate immune response. Triptolide, an active component purified from the medicinal plant Tripterygium Wilfordii Hook F., is a potent immunosuppressive drug capable of prolonging allograft survival in organ transplantation by inhibiting T cell activation and proliferation. Considering the essential role in T cell tolerance of DC migration to secondary lymphoid organs, here we demonstrate that triptolide can significantly inhibit LPS-triggered upregulation of CCR7 expression and PGE(2) production by inhibiting cyclooxygenase-2 (COX-2) expression in DC, thus impairing DC migration towards CCR7 ligand CCL19/MIP-3betain vitro. Moreover, triptolide-treated DC display impaired migration into secondary lymphoid organs and in vivo administration of triptolide also inhibits DC migration. Further studies show that the triptolide-mediated inhibitory effects of LPS-induced activation of phosphatidylinositol-3 kinase (PI3-K)/Akt and nuclear NF-kappaB activation are involved in down-regulation of COX-2 and CCR7 expression resulting in impaired migration to secondary lymphoid organs of DC. Therefore, inhibition of DC migration through decreasing COX-2 and CCR7 expression via PI3-K/Akt and NF-kappaB signal pathways provides additional mechanistic explanation for triptolide's immunosuppressive effect.

Immunosuppressant triptolide inhibits dendritic cell-mediated chemoattraction of neutrophils and T cells through inhibiting Stat3 phosphorylation and NF-kappaB activation.

Triptolide, an active component purified from the medicinal plant Tripterygium wilfordii Hook F., is potent in anti-inflammation and immunosuppression. Dendritic cells (DC), one of important targets of immunosuppressants, play crucial roles in linking the innate immunity and adaptive immunity. However, the effects of triptolide on DC have not been fully elucidated. Chemoattraction of neutrophils and T cells by DC may favor their interactions and initiation of immune response. Here we demonstrate that triptolide significantly impairs DC-mediated chemoattraction of neutrophils and T cells both in vitro and in vivo by suppressing DC production of CC and CXC chemokines including MIP-1alpha, MIP-1beta, MCP-1, RANTES, TARC, and IP-10 in response to LPS. Furthermore, triptolide-mediated inhibition of NF-kappaB activation, Stat3 phosphorylation and increase of SOCS1 expression in DC may be involved in the inhibitory effect of triptolide. Our study provides a novel mechanistic explanation for the anti-inflammatory and immunosuppressive activities of triptolide.

Requirement for ERK activation in sinomenine-induced apoptosis of macrophages.

Sinomenine (SN), an immunnosuppressive compound derived from the Chinese medicinal plant Sinomenium acutum, has been used to treat autoimmune diseases effectively. Previous studies show SN can inhibit lymphocytes proliferation and macrophage production of pro-inflammatory factors. However, little is known about the mechanisms by which SN inhibits macrophage functions. In this study, we demonstrated that SN could inhibit the proliferation of murine macrophages RAW264.7 by inducing apoptosis in a dose- and time-dependent manner. We found activation of extracellular signal-regulated protein kinase (ERK) in SN-treated macrophages, and requirement for ERK activation in SN-induced apoptosis of macrophages. Contemporarily, the expression of p27/KIP1, proapoptotic factor Bax increased, and expression of Bcl-2 decreased, which might cooperate to induce apoptosis. Inhibiting ERK activation reduced the increased expression of p27 and Bax, but had no effect on the decreased expression of Bcl-2, suggesting the involvement of ERK activation in the SN-induced increased expression of p27 and Bax. These results demonstrated that SN could induce apoptosis of macrophages through activation of ERK, and ERK activation might partially involve in the increased expression of p27 and Bax in apoptotic macrophages. Therefore, induction of macrophage apoptosis through ERK activation may be one of mechanisms by which SN exhibits its immunosuppressive function.

Triptolide (PG-490) induces apoptosis of dendritic cells through sequential p38 MAP kinase phosphorylation and caspase 3 activation.

Dendritic cells (DCs) are the most potent antigen-presenting cells that play crucial roles in the regulation of immune response. Triptolide, an active component purified from the medicinal plant Tripterygium wilfordii Hook F., has been demonstrated to act as a potent immunosuppressive drug capable of inhibiting T cell activation and proliferation. However, little is known about the effects of triptolide on DCs. The present study shows that triptolide does not affect phenotypic differentiation and LPS-induced maturation of murine DCs. But triptolide can dramatically reduce cell recovery by inducing apoptosis of DCs at concentration as low as 10ng/ml, as demonstrated by phosphatidylserine exposure, mitochondria potential decrease, and nuclear DNA condensation. Triptolide induces activation of p38 in DCs, which precedes the activation of caspase 3. SB203580, a specific kinase inhibitor for p38, can block the activation of caspase 3 and inhibit the resultant apoptosis of DCs. Our results suggest that the anti-inflammatory and immunosuppressive activities of triptolide may be due, in part, to its apoptosis-inducing effects on DCs.