Triptolide, a constituent of immunosuppressive Chinese herbal medicine, is a potent suppressor of dendritic-cell maturation and trafficking

Increased intracellular, cell surface, and secreted inducible heat shock protein 70 responses are triggered during the monocyte to dendritic cell (DC) transition by cytokines independently of heat stress and infection and may positively regulate DC growth

Physiologic triggers and functional consequences of endogenous heat shock protein (HSP) responses in dendritic cells (DC) are poorly defined. In this study, we show that even in the absence of heat stress and infection, a specific cohort of DC/proinflammatory cytokines (IL-4-IL-13/IL-6/GM-CSF) institutes an enhanced inducible (i)HSP70 intracellular and extracellular response in human monocyte-derived DC, especially during the monocyte to DC transition. Interestingly, whereas heat stress alone initiated an intracellular iHSP70 response in monocyte DC precursors, it did not promote cell surface or secreted iHSP70 responses, both of which were induced by cytokines independently of heat. The cytokine-induced iHSP70 response, which did not occur in lymphocytes, or monocytes-macrophages generated with M-CSF, was instituted within 48 h of cytokine exposure, and peaked upon commitment to DC growth at 72 h. Although a return to baseline levels was noted after this period, a distinct rise in iHSP70 occurred again during terminal DC maturation. Chemical inhibition of the iHSP70 response with either triptolide or KNK-437 was coupled with inhibition of DC differentiation and yielded cells displaying features of monocytes-macrophages. Exogenously supplied riHSP70 amplified events associated with cytokine-advanced DC differentiation/maturation, most notably the up-regulation of antiapoptotic proteins (Bcl-x(L)). Engaging the HSP receptor CD40 with CD40L produced identical results as extracellular riHSP70, and, moreover, an enhanced iHSP70 response. Thus, distinct iHSP70 and HSP receptor-mediated responses are triggered by cytokines irrespective of heat stress and infection in monocyte-derived DC and may function to positively regulate monocyte-derived DC, especially during critical periods of their growth.

Triptolide promotes generation of FoxP3+ T regulatory cells in rats

ETHNOPHARMACOLOGICAL RELEVANCE

Triptolide (TPT), a component of the Chinese herb Triptergium wilfordii, has potent immunosuppressive and anti-inflammatory activity and is used clinically in recipients of kidney transplantation.

AIM OF THE STUDY

This work aimed to investigate the effect of TPT on the differentiation of regulatory T lymphocytes (Tregs) from CD4+ cells in rats.

MATERIALS AND METHODS

MACS-purified rat CD4+ cells were costimulated with anti-CD3 and anti-CD28 in the presence of TGF-beta to induce the expression of FoxP3, which was detected by flow cytometry. TPT and cyclosporine A (CsA) were separately added into the cultures to observe the effect on the expression of FoxP3. Kidney transplantation was performed in rats that either received no treatment or were treated with TPT after transplantation.

RESULTS

TPT treatment enhanced the expression of FoxP3 in CD4+ cells, whereas CsA inhibited the FoxP3 expression. In the rat kidney transplantation model, the recipient rats treated with TPT survived longer than the control rats (18-19.83 vs 6.83 days, P<0.05). Meanwhile, the FoxP3+ T cells in the spleens of treated rats were higher than those from the untreated rats (12.4% vs 4.7%, P<0.05).

CONCLUSIONS

These data suggest that TPT may promote the differentiation of CD4+ cells to FoxP3+ Tregs. This would be at least one of the pathways responsible for the immunosuppressive activity of TPT.

Triptolide induces anti-inflammatory cellular responses

Tripterygium wilfordii Hook F. has been used for centuries in traditional Chinese medicine to treat rheumatoid arthritis, an autoimmune disease associated with increased production of the pro-inflammatory cytokine, tumor necrosis factor (TNF)-alpha. Triptolide is a compound originally purified from T. wilfordii Hook F. and has potent anti-inflammatory and immunosuppressant activities. In this study, we investigated the effect of triptolide on the global gene expression patterns of macrophages treated with lipopolysaccharide (LPS). We found that LPS stimulation resulted in >5-fold increase in expression of 117 genes, and triptolide caused a >50% inhibition in 47 of the LPS-inducible 117 genes. A large portion of the genes that were strongly induced by LPS and significantly inhibited by triptolide were pro-inflammatory cytokine and chemokine genes, including TNF-alpha, IL-1beta, and IL-6. Interestingly, LPS also induced the expression of micro-RNA-155 (miR-155) precursor, BIC, which was inhibited by triptolide. Confirming the cDNA array results, we demonstrated that triptolide blocked the induction of these pro-inflammatory cytokines as well as miR-155 in a dose-dependent manner. Profound inhibition of pro-inflammatory cytokine expression was observed at concentrations as low as 10-50 nM. However, triptolide neither inhibited the phosphorylation or degradation of IkappaBalpha after LPS stimulation, nor affected the DNA-binding activity of NF-kappaB. Surprisingly, we found that triptolide not only inhibited NF-kappaB-regulated reporter transcription, but also dramatically blocked the activity of other transcription factors. Our study offers a plausible explanation of the therapeutic mechanism of T. wilfordii Hook F.

Incorporation of CD40 ligand into the envelope of pseudotyped single-cycle Simian immunodeficiency viruses enhances immunogenicity

A vaccine for the prevention of human immunodeficiency virus (HIV) infection is desperately needed to control the AIDS pandemic. To address this problem, we developed vesicular stomatitis virus glycoprotein-pseudotyped replication-defective simian immunodeficiency viruses (dSIVs) as an AIDS vaccine strategy. The dSIVs retain characteristics of a live attenuated virus without the drawbacks of potential virulence caused by replicating virus. To improve vaccine immunogenicity, we incorporated CD40 ligand (CD40L) into the dSIV envelope. CD40L is one of the most potent stimuli for dendritic cell (DC) maturation and activation. Binding of CD40L to its receptor upregulates expression of major histocompatibility complex class I, class II, and costimulatory molecules on DCs and increases production of proinflammatory cytokines and chemokines, especially interleukin 12 (IL-12). This cytokine polarizes CD4(+) T cells to Th1-type immune responses. DC activation and mixed lymphocyte reaction (MLR) studies were performed to evaluate the immunogenicity of CD40L-dSIV in vitro. Expression levels of CD80, CD86, HLA-DR, and CD54 on DCs transduced with the dSIV incorporating CD40L (CD40L-dSIV) were significantly higher than on those transduced with dSIV. Moreover, CD40L-dSIV-transduced DCs expressed up to 10-fold more IL-12 than dSIV-transduced DCs. CD40L-dSIV-transduced DCs enhanced proliferation and gamma interferon secretion by naive T cells in an MLR. In addition, CD40L-dSIV-immunized mice exhibited stronger humoral and cell-mediated immune responses than dSIV-vaccinated animals. The results show that incorporating CD40L into the dSIV envelope significantly enhances immunogenicity. As a result, CD40L-dSIVs can be strong candidates for development of a safe and highly immunogenic AIDS vaccine.

Combined treatment with triptolide and rapamycin prolongs graft survival in a mouse model of cardiac transplantation

Current immunosuppressive strategies for transplantation have failed to achieve long-term graft survival. In this study, we investigate the effects of combined treatment with triptolide (TPT) and rapamycin (Rapa) on graft survival as well as changes in pathology and immunological responses. Heterotopic heart transplantation was performed. TPT and Rapa were administered either alone or in combination. The mean survival time (MST) for the cardiac allografts in animals receiving the combination of TPT and Rapa was 93.5 +/- 6.7 days compared to treatment with TPT (MST: 23.5 +/- 5.3 days), Rapa (22 +/- 1.3 days) alone or no treatment (7.66 +/- 0.8 days). Histopathological evaluation showed that inflammatory cell infiltration was markedly reduced in grafts with combined treatment groups. Down-regulation of CCL19, CCR5, CCR7, interferon gamma and interleukin (IL)-12 in the combination treatment was accompanied by increased expression of IL-4, IL-10 and CD4(+)CD25(+)Foxp3(+) regulatory T (Tr) cells in spleen. Finally, dendritic cell (DC) maturation was impaired by treatment with TPT/Rapa. Our results demonstrate that combination therapy with TPT and Rapa markedly prolongs cardiac allograft survival. This effect is accompanied by inhibition of DCs maturation, conditioning DCs to adopt tolerogenic phenotype, and the expansion of Tr cells. These results add weight to the application of combination therapy in transplantation.

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.

Regulatory T cells, a potent immunoregulatory target for CAM researchers: modulating tumor immunity, autoimmunity and alloreactive immunity (III)

Regulatory T (T(reg)) cells are the major arbiter of immune responses, mediating actions through the suppression of inflammatory and destructive immune reactions. Inappropriate T(reg) cell frequency or functionality potentiates the pathogenesis of myriad diseases with ranging magnitudes of severity. Lack of suppressive capability hinders restraint on immune responses involved in autoimmunity and alloreactivity, while excessive suppressive capacity effectively blocks processes necessary for tumor destruction. Although the etiology of dysfunctional T(reg) cell populations is under debate, the ramifications, and their mechanisms, are increasingly brought to light in the medical community. Methods that compensate for aberrant immune regulation may not address the underlying complications; however, they hold promise for the alleviation of debilitating immune system-related disorders. The dominant immunoregulatory nature of T(reg) cells, coupled with recent mechanistic knowledge of natural immunomodulatory compounds, highlights the importance of T(reg) cells to practitioners and researchers of complementary and alternative medicine (CAM).

Permanent Survival of Fully MHC-Mismatched Islet Allografts by Targeting a Single Chemokine Receptor Pathway

Chemokine receptor blockade can diminish the recruitment of host effector cells and prolong allograft survival, but little is known of the role of chemokine receptors in promoting host sensitization. We engrafted fully allogeneic islets into streptozotocin-treated normal mice or mice with the autosomal recessive paucity of lymph node T cell (plt) mutation; the latter lack secondary lymphoid expression of the CCR7 ligands, secondary lymphoid organ chemokine (CCL21) and EBV-induced molecule-1 ligand chemokine (CCL19). plt mice showed permanent survival of islets engrafted under the kidney capsule, whereas controls rejected islet allografts in 12 days (p < 0.001), and consistent with this, plt mice had normal allogeneic T cell responses, but deficient migration of donor dendritic cell to draining lymph nodes. Peritransplant i.v. injection of donor splenocytes caused plt recipients to reject their allografts by 12 days, and sensitization at 60 days posttransplant of plt mice with well-functioning allografts restored acute rejection. Finally, islet allografts transplanted intrahepatically in plt mice were rejected approximately 12 days posttransplant, like controls, as were primarily revascularized cardiac allografts. These data show that the chemokine-directed homing of donor dendritic cell to secondary lymphoid tissues is essential for host sensitization and allograft rejection. Interruption of such homing can prevent T cell priming and islet allograft rejection despite normal T and B cell functions of the recipient, with potential clinical implications.