The karyopherin CRM1 is required for dendritic cell maturation

Dendritic cells (DC) are the most potent antigen-presenting cells (APC) of the immune system and are specialized to activate T as well as B cell-dependent immune responses. Mature DC are characterized by expression of CD83, a surface molecule that has been postulated to be required for efficient DC activity. Here we show that Leptomycin B (LMB), a highly specific inhibitor of the nuclear export receptor CRM1, abrogates the ability of DC to stimulate T cells in an allogeneic mixed lymphocyte reaction. Interestingly, this effect correlates with down-regulation of CD83, CD80 and CD86 surface expression during DC maturation, whereas other investigated DC surface molecules, such as MHC class I and II molecules are not significantly affected. Analysis of RNA distribution reveals that particularly the stimulated expression of CD83 depended on a functional CRM1 export receptor. Taken together, the presented data show a critical involvement of the CRM1 transport receptor in DC maturation, most likely by enabling efficient nucleo-cytoplasmic translocation of specific mRNAs. Thus, interference with this pathway may provide new strategies to modulate DC function and, subsequently, DC-mediated immune responses.

Hypoxia and hypoxia-inducible factor-1 alpha modulate lipopolysaccharide-induced dendritic cell activation and function

Dendritic cells (DC) play a key role in linking innate and adaptive immunity. In inflamed tissues, where DC become activated, oxygen tensions are usually low. Although hypoxia is increasingly recognized as an important determinant of cellular functions, the consequences of hypoxia and the role of one of the key players in hypoxic gene regulation, the transcription factor hypoxia inducible factor 1alpha (HIF-1alpha), are largely unknown. Thus, we investigated the effects of hypoxia and HIF-1alpha on murine DC activation and function in the presence or absence of an exogenous inflammatory stimulus. Hypoxia alone did not activate murine DC, but hypoxia combined with LPS led to marked increases in expression of costimulatory molecules, proinflammatory cytokine synthesis, and induction of allogeneic lymphocyte proliferation compared with LPS alone. This DC activation was accompanied by accumulation of HIF-1alpha protein levels, induction of glycolytic HIF target genes, and enhanced glycolytic activity. Using RNA interference techniques, knockdown of HIF-1alpha significantly reduced glucose use in DC, inhibited maturation, and led to an impaired capability to stimulate allogeneic T cells. Alltogether, our data indicate that HIF-1alpha and hypoxia play a crucial role for DC activation in inflammatory states, which is highly dependent on glycolysis even in the presence of oxygen.

Small interfering RNA (siRNA) delivery into murine bone marrow-derived dendritic cells by electroporation

Selective gene silencing by RNA interference (RNAi) has been shown to be an efficient method for the targeted manipulation of cellular functions. In this study we describe for the first time electroporation as a suitable and efficient method for the delivery of small interfering RNA (siRNA) into murine bone marrow-derived dendritic cells (BM-DC). Using a fluorescein-labeled non-silencing siRNA duplex, we established an electroporation protocol yielding routinely >90% positive cells. We investigated the effects of siRNA electroporation on BM-DC viability, phenotype and ability to induce allogeneic T cell proliferation. Finally, using siRNAs directed against MAPK1 and the transcription factor HIF-1alpha we were able to demonstrate an efficient knock down of cellular mRNA- and protein level in electroporated BM-DC. Furthermore, knocking down the transcription factor HIF-1alpha impeded hypoxic induction of HIF-1alpha target genes. We therefore propose siRNA electroporation into murine BM-DC as an efficient method to manipulate BM-DC function without the use of chemical transfection reagents. This new approach is superior to lipofection regarding detrimental effects of lipid-based transfection agents on BM-DC immunobiology.

MCS-18, a novel natural product isolated from Helleborus purpurascens, inhibits dendritic cell activation and prevents autoimmunity as shown in vivo using the EAE model

Here we report for the first time that MCS-18, a novel natural product isolated from Helleborus purpurascens, is able to inhibit the expression of typical molecules of mature dendritic cells (DC) such as CD80, CD86, and especially of CD83 subsequently leading to a clear and dose-dependent inhibition of the DC-mediated T-cell stimulation. Furthermore, MCS-18 impeded the formation of the typical DC/T-cell clusters, which are essential to induce potent immune responses. Interestingly, MCS-18 also inhibited CCR7 expression on DC which subsequently lead to a dose-dependent block of the CCL19-mediated DC migration. MCS-18 not only inhibited the DC-mediated T-cell stimulation but also the anti-CD3/anti-CD28-mediated T-cell stimulation. Strikingly, MCS-18 also strongly reduced the paralysis associated with the experimental autoimmune encephalomyelitis (EAE), which is a murine model for human multiple sclerosis, in a prophylactic as well as in a "real" therapeutic setting. Even when the EAE was induced for a second time, the MCS-18-treated animals were still protected, suggesting that MCS-18 induces a long-lasting suppressive effect. In addition, and very important for the potential practical application in humans, MCS-18 was also active when administered orally. MCS-18 treatment almost completely reduced leukocyte infiltration in the brain and in the spinal cord. In conclusion, using in vitro as well in vivo assays we were able to show that MCS-18 exerts a strong immunosuppressive activity with remarkable potential for the therapy of diseases characterized by a pathologically over-activated immune system.

DC-SIGN and DC-SIGNR interact with the glycoprotein of Marburg virus and the S protein of severe acute respiratory syndrome coronavirus

The lectins DC-SIGN and DC-SIGNR can augment viral infection; however, the range of pathogens interacting with these attachment factors is incompletely defined. Here we show that DC-SIGN and DC-SIGNR enhance infection mediated by the glycoprotein (GP) of Marburg virus (MARV) and the S protein of severe acute respiratory syndrome coronavirus and might promote viral dissemination. SIGNR1, a murine DC-SIGN homologue, also enhanced infection driven by MARV and Ebola virus GP and could be targeted to assess the role of attachment factors in filovirus infection in vivo.

CNI-1493 mediated suppression of dendritic cell activation in vitro and in vivo

The tetravalent guanylhydrazone CNI-1493 (CNI-1493) has been shown to inhibit macrophage activation, reduce systemic inflammation as well as proinflammatory cytokine production. Here we report for the first time that CNI-1493 also influences the biology of dendritic cells (DC). In order to become potent T cell stimulators of DC have to mature. Interestingly, when CNI-1493 was added to the maturation stimulus the expression of a typical DC-maturation marker i.e. CD83 was reduced. Subsequent functional in vitro analyses showed that DC-mediated T-cell stimulation was clearly reduced in CNI-1493-treated DC, underlining the functional impact that CNI-1493 on DC biology. Furthermore, the effect of CNI-1493 was analyzed in vivo using the experimental autoimmune encephalomyelitis (EAE) model in C57BL/6 mice. Interestingly, in a prophylactic treatment regimen CNI-1493 prevented the paralysis associated with EAE almost completely. In addition, when applied in an early therapeutic setting CNI-1493 also reduced the clinical EAE symptoms. In summary, we show for the first time, that in addition to the earlier reported effects on macrophages, CNI-1493 also influences the function and biology of DC. Since DC are the only antigen-presenting cells (APC) known today to be able to prime naive T cells, the findings reported herein are highly relevant for the therapeutic application of CNI-1493.

Histologic and immunophenotypic evaluation of pretreatment renal biopsies in OKT3-treated allograft rejections

The histologic features immunophenotype of intragraft mononuclear populations, and HLA-Dr expression in pretreatment formalin-fixed renal allograft biopsies were correlated with outcome of OKT3 therapy in 35 steroid resistant renal transplant rejections. Therapeutic response (63% overall) was better in pure acute cellular rejections (ACR) (13/15, 87%) than ACR with interstitial fibrosis (4/12, 33%) or with vascular injury (5/8, 62%). Intragraft T lymphocytes were more numerous in vascular rejection (mean 566/mm2) compared with pure ACR (mean 265/mm2, P = .049), and macrophages were greater in pure ACR (203/mm2) compared with ACR with interstitial fibrosis (83/mm2, P = .051). Distribution of T cells, B cells, plasma cells, and macrophages among various histologic categories was otherwise statistically similar. There was no correlation between therapeutic response to OKT3 and intragraft concentrations of individual mononuclear cell subsets. Vascular and/or epithelial HLA-Dr expression was present in 17/25 (68%) cases and was not associated with histologic features or treatment response. Follow-up graft function (median 7 months) correlated significantly with therapeutic response to OKT3 (P = .0004) and histologic presence of interstitial fibrosis (P = .031), but was not related to concentration of individual mononuclear subsets or HLA-Dr expression. We conclude that intragraft concentrations of major mononuclear cell types may relate to histology, but that these do not predict treatment response or graft outcome, and thus poorly reflect intensity or possible heterogeneity of host immunologic rejection mechanisms.