Correction: Comprehensive Analysis of Human Cytomegalovirus MicroRNA Expression during Lytic and Quiescent Infection.

[This corrects the article DOI: 10.1371/journal.pone.0088531.].

Aquaphilus dolomiae extract counteracts the effects of cutaneous S. aureus secretome isolated from atopic children on CD4+ T cell activation.

CONTEXT: Skin microbiota takes part in the control of cutaneous inflammation. In skin diseases such as atopic dermatitis (AD) cutaneous dysbiosis and the emergence of Staphylococcus aureus contribute to the pathophysiology of the disease. New therapeutic approaches consist in topical application of natural products able to counteract S. aureus effects through activation of resident immune cells producing anti-inflammatory cytokines such as IL-10. OBJECTIVE: This study investigates the potential immunosuppressive properties of Aquaphilus dolomiae (Neisseriaceae), a flagellated bacterium contained in Avène Thermal Spring Water used in hydrotherapy treatments of AD patients. MATERIALS AND METHODS: An aqueous protein extract of Aquaphilus dolomiae (ADE, 60 µg/mL) was added to human monocyte-derived dendritic cells (moDC) for 24 h. Expression of HLA-DR, CD86 and CD83 was evaluated by flow cytometry and released cytokines (IL-10, IL-12) by cytometry bead array assay. The proliferation of allogeneic CFSE-labelled CD4+ T cells stimulated with ADE-conditioned moDC and S. aureus secretome was analysed by flow cytometry. RESULTS: MoDC exposed to ADE expressed lower levels of HLA-DR and CD86 than untreated cells, no CD83 and secreted barely detectable IL-12 but high amounts of IL-10 (N = 12, p < 0.0002). The proliferative effect of S. aureus secretome on CD4+ T cells was reduced (p < 0.001) in the presence of ADE-moDC. CONCLUSION: ADE counteracted the mitogenic effect of a S. aureus secretome on CD4+T cells. Owing to the role of S. aureus colonization in driving inflammation in AD the immunosuppressive property of the ADE might be useful to reduce disease severity.

PPARγ Is Activated during Congenital Cytomegalovirus Infection and Inhibits Neuronogenesis from Human Neural Stem Cells.

Congenital infection by human cytomegalovirus (HCMV) is a leading cause of permanent sequelae of the central nervous system, including sensorineural deafness, cerebral palsies or devastating neurodevelopmental abnormalities (0.1% of all births). To gain insight on the impact of HCMV on neuronal development, we used both neural stem cells from human embryonic stem cells (NSC) and brain sections from infected fetuses and investigated the outcomes of infection on Peroxisome Proliferator-Activated Receptor gamma (PPARγ), a transcription factor critical in the developing brain. We observed that HCMV infection dramatically impaired the rate of neuronogenesis and strongly increased PPARγ levels and activity. Consistent with these findings, levels of 9-hydroxyoctadecadienoic acid (9-HODE), a known PPARγ agonist, were significantly increased in infected NSCs. Likewise, exposure of uninfected NSCs to 9-HODE recapitulated the effect of infection on PPARγ activity. It also increased the rate of cells expressing the IE antigen in HCMV-infected NSCs. Further, we demonstrated that (1) pharmacological activation of ectopically expressed PPARγ was sufficient to induce impaired neuronogenesis of uninfected NSCs, (2) treatment of uninfected NSCs with 9-HODE impaired NSC differentiation and (3) treatment of HCMV-infected NSCs with the PPARγ inhibitor T0070907 restored a normal rate of differentiation. The role of PPARγ in the disease phenotype was strongly supported by the immunodetection of nuclear PPARγ in brain germinative zones of congenitally infected fetuses (N = 20), but not in control samples. Altogether, our findings reveal a key role for PPARγ in neurogenesis and in the pathophysiology of HCMV congenital infection. They also pave the way to the identification of PPARγ gene targets in the infected brain.

Aminobisphosphonates Synergize with Human Cytomegalovirus To Activate the Antiviral Activity of Vγ9Vδ2 Cells.

Human Vγ9Vδ2 T cells are activated through their TCR by neighboring cells producing phosphoantigens. Zoledronate (ZOL) treatment induces intracellular accumulation of the phosphoantigens isopentenyl pyrophosphate and ApppI. Few attempts have been made to use immunomanipulation of Vγ9Vδ2 lymphocytes in chronic viral infections. Although Vγ9Vδ2 T cells seem to ignore human CMV (HCMV)-infected cells, we examined whether they can sense HCMV when a TCR stimulus is provided with ZOL. Fibroblasts treated with ZOL activate Vγ9Vδ2 T cells to produce IFN-γ but not TNF. Following the same treatment, HCMV-infected fibroblasts stimulate TNF secretion and an increased production of IFN-γ, indicating that Vγ9Vδ2 cells can sense HCMV infection. Increased lymphokine production was observed with most clinical isolates and laboratory HCMV strains, HCMV-permissive astrocytoma, or dendritic cells, as well as "naive" and activated Vγ9Vδ2 cells. Quantification of intracellular isopentenyl pyrophosphate/ApppI following ZOL treatment showed that HCMV infection boosts their accumulation. This was explained by an increased capture of ZOL and by upregulation of HMG-CoA synthase and reductase transcription. Using an experimental setting where infected fibroblasts were cocultured with γδ cells in submicromolar concentrations of ZOL, we show that Vγ9Vδ2 cells suppressed substantially the release of infectious particles while preserving uninfected cells. Vγ9Vδ2 cytotoxicity was decreased by HCMV infection of targets whereas anti-IFN-γ and anti-TNF Abs significantly blocked the antiviral effect. Our experiments indicate that cytokines produced by Vγ9Vδ2 T cells have an antiviral potential in HCMV infection. This should lead to in vivo studies to explore the possible antiviral effect of immunostimulation with ZOL in this context.

Effects of the Staphylococcus aureus and Staphylococcus epidermidis Secretomes Isolated from the Skin Microbiota of Atopic Children on CD4+ T Cell Activation.

Interactions between the immune system and skin bacteria are of major importance in the pathophysiology of atopic dermatitis (AD), yet our understanding of them is limited. From a cohort of very young AD children (1 to 3 years old), sensitized to Dermatophagoides pteronyssinus allergens (Der p), we conducted culturomic analysis of skin microbiota, cutaneous transcript profiling and quantification of anti-Der p CD4+ T cells. This showed that the presence of S. aureus in inflamed skin of AD patients was associated with a high IgE response, increased expression of inflammatory and Th2/Th22 transcripts and the prevalence of a peripheral Th2 anti-Der p response. Monocyte-derived dendritic cells (moDC) exposed to the S. aureus and S. epidermidis secretomes were found to release pro-inflammatory IFN-γ and anti-inflammatory IL-10, respectively. Allogeneic moDC exposed to the S. aureus secretome also induced the proliferation of CD4+ T cells and this effect was counteracted by concurrent exposure to the S. epidermidis secretome. In addition, whereas the S. epidermidis secretome promoted the activity of regulatory T cells (Treg) in suppressing the proliferation of conventional CD4+ T cells, the Treg lost this ability in the presence of the S. aureus secretome. We therefore conclude that S. aureus may cause and promote inflammation in the skin of AD children through concomitant Th2 activation and the silencing of resident Treg cells. Commensals such as S. epidermidis may counteract these effects by inducing the release of IL-10 by skin dendritic cells.

Cytomegalovirus Infection Triggers the Secretion of the PPARγ Agonists 15-Hydroxyeicosatetraenoic Acid (15-HETE) and 13-Hydroxyoctadecadienoic Acid (13-HODE) in Human Cytotrophoblasts and Placental Cultures.

INTRODUCTION: Congenital infection by human cytomegalovirus (HCMV) is a leading cause of congenital abnormalities of the central nervous system. Placenta infection by HCMV allows for viral spread to fetus and may result in intrauterine growth restriction, preeclampsia-like symptoms, or miscarriages. We previously reported that HCMV activates peroxisome proliferator-activated receptor gamma (PPARγ) for its own replication in cytotrophoblasts. Here, we investigated the molecular bases of PPARγ activation in infected cytotrophoblasts. RESULTS: We show that onboarded cPLA2 carried by HCMV particles is required for effective PPARγ activation in infected HIPEC cytotrophoblasts, and for the resulting inhibition of cell migration. Natural PPARγ agonists are generated by PLA2 driven oxidization of linoleic and arachidonic acids. Therefore, using HPLC coupled with mass spectrometry, we disclosed that cellular and secreted levels of 13-hydroxyoctadecadienoic acid (13-HODE) and 15-hydroxyeicosatetraenoic acid (15-HETE) were significantly increased in and from HIPEC cytotrophoblasts at soon as 6 hours post infection. 13-HODE treatment of uninfected HIPEC recapitulated the effect of infection (PPARγ activation, migration impairment). We found that infection of histocultures of normal, first-term, human placental explants resulted in significantly increased levels of secreted 15-HETE and 13-HODE. CONCLUSION: Our findings reveal that 15-HETE and 13-HODE could be new pathogenic effectors of HCMV congenital infection They provide a new insight about the pathogenesis of congenital infection by HCMV.

MicroRNA miR-21 attenuates human cytomegalovirus replication in neural cells by targeting Cdc25a.

UNLABELLED: Congenital human cytomegalovirus (HCMV) infection is a leading cause of birth defects, primarily manifesting as neurological disorders. HCMV infection alters expression of cellular microRNAs (miRs) and induces cell cycle arrest, which in turn modifies the cellular environment to favor virus replication. Previous observations found that HCMV infection reduces miR-21 expression in neural progenitor/stem cells (NPCs). Here, we show that infection of NPCs and U-251MG cells represses miR-21 while increasing the levels of Cdc25a, a cell cycle regulator and known target of miR-21. These opposing responses to infection prompted an investigation of the relationship between miR-21, Cdc25a, and viral replication. Overexpression of miR-21 in NPCs and U-251MG cells inhibited viral gene expression, genome replication, and production of infectious progeny, while shRNA-knockdown of miR-21 in U-251MG cells increased viral gene expression. In contrast, overexpression of Cdc25a in U-251MG cells increased viral gene expression and production of infectious progeny and overcame the inhibitory effects of miR-21 overexpression. Three viral gene products-IE1, pp71, and UL26-were shown to inhibit miR-21 expression at the transcriptional level. These results suggest that Cdc25a promotes HCMV replication and elevation of Cdc25a levels after HCMV infection are due in part to HCMV-mediated repression of miR-21. Thus, miR-21 is an intrinsic antiviral factor that is modulated by HCMV infection. This suggests a role for miR-21 downregulation in the neuropathogenesis of HCMV infection of the developing CNS. IMPORTANCE: Human cytomegalovirus (HCMV) is a ubiquitous pathogen and has very high prevalence among population, especially in China, and congenital HCMV infection is a major cause for birth defects. Elucidating virus-host interactions that govern HCMV replication in neuronal cells is critical to understanding the neuropathogenesis of birth defects resulting from congenital infection. In this study, we confirm that HCMV infection downregulates miR-21 but upregulates Cdc25a. Further determined the negative effects of cellular miRNA miR-21 on HCMV replication in neural progenitor/stem cells and U-251MG glioblastoma/astrocytoma cells. More importantly, our results provide the first evidence that miR-21 negatively regulates HCMV replication by targeting Cdc25a, a vital cell cycle regulator. We further found that viral gene products of IE1, pp71, and UL26 play roles in inhibiting miR-21 expression, which in turn causes increases in Cdc25a and benefits HCMV replication. Thus, miR-21 appears to be an intrinsic antiviral factor that represents a potential target for therapeutic intervention.

Comprehensive analysis of human cytomegalovirus microRNA expression during lytic and quiescent infection.

BACKGROUND: Human cytomegalovirus (HCMV) encodes microRNAs (miRNAs) that function as post-transcriptional regulators of gene expression during lytic infection in permissive cells. Some miRNAs have been shown to suppress virus replication, which could help HCMV to establish or maintain latent infection. However, HCMV miRNA expression has not been comprehensively examined and compared using cell culture systems representing permissive (lytic) and semi-permissive vs. non-permissive (latent-like) infection. METHODS: Viral miRNAs levels and expression kinetics during HCMV infection were determined by miRNA-specific stem-loop RT-PCR. HCMV infected THP-1 (non-permissive), differentiated THP-1 (d-THP-1, semi-permissive) and human embryo lung fibroblasts (HELs, fully-permissive) were examined. The impact of selected miRNAs on HCMV infection (gene expression, genome replication and virus release) was determined by Western blotting, RT-PCR, qPCR, and plaque assay. RESULTS: Abundant expression of 15 HCMV miRNAs was observed during lytic infection in HELs; highest peak inductions (11- to 1502-fold) occurred at 48 hpi. In d-THP-1s, fourteen mRNAs were detected with moderate induction (3- to 288-fold), but kinetics of expression was generally delayed for 24 h relative to HELs. In contrast, only three miRNAs were induced to low levels (3- to 4-fold) during quiescent infection in THP-1s. Interestingly, miR-UL70-3p was poorly induced in HEL (1.5-fold), moderately in THP-1s (4-fold), and strongly (58-fold) in d-THP-1s, suggesting a potentially specific role for miR-UL70-3p in THP-1s and d-THP-1s. MiR-US33, -UL22A and -UL70 were further evaluated for their impact on HCMV replication in HELs. Ectopic expression of miR-UL22A and miR-UL70 did not affect HCMV replication in HELs, whereas miR-US33 inhibited HCMV replication and reduced levels of HCMV US29 mRNA, confirming that US29 is a target of miR-US33. CONCLUSIONS: Viral miRNA expression kinetics differs between permissive, semi-permissive and quiescent infections, and miR-US33 down-regulates HCMV replication. These results suggest that miR-US33 may function to impair entry into lytic replication and hence promote establishment of latency.

Maintenance of large numbers of virus genomes in human cytomegalovirus-infected T98G glioblastoma cells.

UNLABELLED: After infection, human cytomegalovirus (HCMV) persists for life. Primary infections and reactivation of latent virus can both result in congenital infection, a leading cause of central nervous system birth defects. We previously reported long-term HCMV infection in the T98G glioblastoma cell line (1). HCMV infection has been further characterized in T98Gs, emphasizing the presence of HCMV DNA over an extended time frame. T98Gs were infected with either HCMV Towne or AD169-IE2-enhanced green fluorescent protein (eGFP) strains. Towne infections yielded mixed IE1 antigen-positive and -negative (Ag(+)/Ag(-)) populations. AD169-IE2-eGFP infections also yielded mixed populations, which were sorted to obtain an IE2(-) (Ag(-)) population. Viral gene expression over the course of infection was determined by immunofluorescent analysis (IFA) and reverse transcription-PCR (RT-PCR). The presence of HCMV genomes was determined by PCR, nested PCR (n-PCR), and fluorescence in situ hybridization (FISH). Compared to the HCMV latency model, THP-1, Towne-infected T98Gs expressed IE1 and latency-associated transcripts for longer periods, contained many more HCMV genomes during early passages, and carried genomes for a greatly extended period of passaging. Large numbers of HCMV genomes were also found in purified Ag(-) AD169-infected cells for the first several passages. Interestingly, latency transcripts were observed from very early times in the Towne-infected cells, even when IE1 was expressed at low levels. Although AD169-infected Ag(-) cells expressed no detectable levels of either IE1 or latency transcripts, they also maintained large numbers of genomes within the cell nuclei for several passages. These results identify HCMV-infected T98Gs as an attractive new model in the study of the long-term maintenance of virus genomes in the context of neural cell types. IMPORTANCE: Our previous work showed that T98G glioblastoma cells were semipermissive to HCMV infection; virus trafficked to the nucleus, and yet only a proportion of cells stained positive for viral antigens, thus allowing continual subculturing and passaging. The cells eventually transitioned to a state where viral genomes were maintained without viral antigen expression or virion production. Here we report that during long-term T98G infection, large numbers of genomes were maintained within all of the cells' nuclei for the first several passages (through passage 4 [P4]), even in the presence of continual cellular division. Surprisingly, genomes were maintained, albeit at a lower level, through day 41. This is decidedly longer than in any other latency model system that has been described to date. We believe that this system offers a useful model to aid in unraveling the cellular components involved in viral genome maintenance (and presumably replication) in cells carrying long-term latent genomes in a neural context.

Paracrine inhibition of GM-CSF signaling by human cytomegalovirus in monocytes differentiating to dendritic cells.

A primary HCMV infection or virus reactivation may cause severe disease in hosts with a deficient immune system. The virus can disturb both innate and adaptive immunity by targeting dendritic cell (DC) functions. Monocytes, the precursors of DCs in vivo (MoDCs), are the primary targets of HCMV; they can also harbor latent virus. The DCs generated from infected monocytes (CMV-MoDCs) have an altered phenotype and functional defects. We have shown that CMV-MoDCs do not secrete IL-12 in response to lipopolysaccharide stimulation, cannot ingest dead cells, induce T(H)1 differentiation, or the proliferation of naive allogeneic CD4(+) T cells. We found that the GM-CSF signaling in an entire population of CMV-MoDCs was impaired, although only half of the cells were productively infected, and that IL-6 secretion and suppressors of cytokine signaling 3 induction contributed to this bystander effect. We also showed that MoDCs derived ex vivo from monocytes of viremic patients had the same altered phenotype as CMV-MoDCs, including decreased STAT5 phosphorylation, indicating defective GM-CSF signaling. We have thus described a new mechanism of HCMV-induced immunosupression, indicated how infection may disturb both GM-CSF-dependent physiologic processes and proposed GM-CSF-based therapeutic approaches.

PPARγ and human trophoblast differentiation.

The peroxisome proliferator-activated receptor-γ (PPARγ) is a member of the nuclear receptor superfamily that controls in a ligand-dependent manner the expression of a large array of genes involved in the control of energy homeostasis and in cell differentiation, proliferation, apoptosis, and the inflammatory process. Unexpectedly, genetic studies performed in mice established that PPARγ is essential for placental development. In the human placenta, PPARγ is specifically expressed in the trophoblast, both endocrine villous and invasive extravillous cytotrophoblasts (EVCT). Activation of PPARγ induces accumulation of lipids, villous trophoblast differentiation and inhibits trophoblast invasiveness. Oxidized LDLs that contain potential PPARγ ligands, but not native LDL, induce PPARγ transcriptional activity and inhibit trophoblast invasion in vitro. Recently, human cytomegalovirus (HCMV) was shown to activate trophoblastic PPARγ for its own replication and consequently inhibits invasiveness of infected cytotrophoblasts. Analysis of PPARγ target genes revealed trophoblastic factors described to control trophoblast invasiveness and surprisingly chorionic gonadotropin hormone (hCG), known to be mainly produced by the endocrine villous trophoblast. Analysis of hCG gene expression revealed opposite regulation by PPARγ in the two trophoblast subtypes. Finally, a hyperglycosylated form of hCG (hCG-H) only produced by invasive EVCT was shown to promote trophoblast invasion. Together, these data underscore the major role of PPARγ and its target genes, such as hCG, in the control of human trophoblast differentiation and invasion, and suggest that over-activation of this nuclear receptor following HCMV infection or by excess of ligands at the maternal-fetal interface could impair implantation and placentation and therefore embryonic development.

Activation of peroxisome proliferator-activated receptor gamma by human cytomegalovirus for de novo replication impairs migration and invasiveness of cytotrophoblasts from early placentas.

Human cytomegalovirus (HCMV) contributes to pathogenic processes in immunosuppressed individuals, in fetuses, and in neonates. In the present report, by using reporter gene activation assays and confocal microscopy in the presence of a specific antagonist, we show for the first time that HCMV infection induces peroxisome proliferator-activated receptor gamma (PPARgamma) transcriptional activity in infected cells. We demonstrate that the PPARgamma antagonist dramatically impairs virus production and that the major immediate-early promoter contains PPAR response elements able to bind PPARgamma, as assessed by electrophoretic mobility shift and chromatin immunoprecipitation assays. Due to the key role of PPARgamma in placentation and its specific trophoblast expression within the human placenta, we then provided evidence that by activating PPARgamma human cytomegalovirus dramatically impaired early human trophoblast migration and invasiveness, as assessed by using well-established in vitro models of invasive trophoblast, i.e., primary cultures of extravillous cytotrophoblasts (EVCT) isolated from first-trimester placentas and the EVCT-derived cell line HIPEC. Our data provide new clues to explain how early infection during pregnancy could impair implantation and placentation and therefore embryonic development.

Specific requirements for Vgamma9Vdelta2 T cell stimulation by a natural adenylated phosphoantigen.

Human Vgamma9Vdelta2 T lymphocytes recognize phosphorylated alkyl Ags. Isopentenyl pyrophosphate (IPP) was previously proposed as the main Ag responsible for Vgamma9Vdelta2 T cell activation by cancer cells. However, triphosphoric acid 1-adenosin-5'-yl ester 3-(3-methylbut-3-enyl) ester (ApppI), a metabolite in which the isopentenyl moiety is linked to ATP, was reported in cells activated with aminobisphosphonates. The contribution of this compound to tumor-stimulatory activity was thus examined. ApppI induces selective expansion of Vgamma9Vdelta2 T cells from PBMCs. In the absence of APCs, however, ApppI has little stimulatory activity on Vgamma9Vdelta2 T cells, and optimal activation with ApppI requires addition of a nucleotide pyrophosphatase releasing IPP plus AMP. Thus, ApppI has no intrinsic stimulatory activity. Nevertheless, stimulation by ApppI is strengthened by the presence of APCs. Moreover, in contrast to IPP, ApppI can be efficiently pulsed on dendritic cells as well as on nonprofessional APCs. Pulsed APCs display stable and phosphatase-resistant stimulatory activity, indicative of Ag modification. HPLC analysis of tumor cell extracts indicates that latent phosphoantigenic activity is stored intracellularly in the Vgamma9Vdelta2 cell-sensitive tumor Daudi and can be activated by a nucleotide pyrophosphatase activity. The presence of ApppI in Daudi cell extracts was demonstrated by mass spectrometry. Nucleotidic Ags such as ApppI are thus a storage form of phosphoantigen which may represent a major source of phosphoantigenic activity in tumor cells. The unique properties of ApppI may be important for the design of Ags used in anticancer immunotherapeutic protocols using Vgamma9Vdelta2 cells.

Bcl-3-regulated transcription from major immediate-early promoter of human cytomegalovirus in monocyte-derived macrophages.

Monocytes/macrophages are key cells in the pathogenesis of human CMV (HCMV) infection, but the in vitro rate of viral production in primary human monocyte-derived macrophages (MDM) is considerably lower than in fibroblasts. Considering that the NF-kappaB signaling pathway is potentially involved in the replication strategy of HCMV through efficient transactivation of the major immediate-early promoter (MIEP), efficient viral replication, and late gene expression, we investigated the composition of the NF-kappaB complex in HCMV-infected MDMs and fibroblasts. Preliminary studies showed that HCMV could grow in primary MDM culture but that the viral titer in culture supernatants was lower than that observed in the supernatants of more permissive MRC5 fibroblasts. EMSA and microwell colorimetric NF-kappaB assay demonstrated that HCMV infection of MDMs increased p52 binding activity without activating the canonical p50/p65 complex. Moreover, Bcl-3 was up-regulated and was demonstrated to associate with p52, indicating p52/Bcl-3 complexes as the major component of the NF-kappaB complex in MDMs. Luciferase assays in promonocytic U937 cells transfected with an MIEP-luciferase reporter construct demonstrated MIEP activation in response to p52 and Bcl-3 overexpression. Chromatin immunoprecipitation assay demonstrated that p52 and Bcl-3 bind the MIEP in acutely HCMV-infected MDMs. In contrast, HCMV infection of MRC5 fibroblasts resulted in activation of p50/p65 heterodimers. Thus, activation of p52/Bcl-3 complexes in MDMs and p50/p65 heterodimers in fibroblasts in response to HCMV infection might explain the low-level growth of the virus in MDMs vs efficient growth in fibroblasts.

Interplay between human cytomegalovirus and dendritic cells in T cell activation.

Control of human cytomegalovirus (HCMV) infection and prevention of associated diseases in immunocompetent hosts are ensured mainly by CD8+ T cells, in spite of numerous viral tricks to impair antigen presentation and activation of T cells. At sites of primary infection, dendritic cells (DCs) are in the forefront to ensure capture of viral antigens and their capacity to bypass the effects of viral immunoevasins is crucial in moulding CD8+ T cell repertoire. In HCMV-seropositive donors, the spectrum of CD8+ T cells specificities was shown to include immediate-early (IE), early (E) and late (L) gene products, a surprising finding if we consider that expression of immunoevasins could paralyse infected DCs from the IE phase of infection. In the present report, we suggest that uninfected dendritic cells could acquire HCMV-antigens derived from input virus or neosynthesis, either in soluble forms or in association with infected dead cells resulting from death-ligand-mediated apoptosis and necrosis. Activation of naïve CD8+ T cells could then occur in lymph nodes through cross-presentation by antigen-loaded DCs, providing an explanation for shape and size of the memory compartment.

Dendritic cell-induced apoptosis of human cytomegalovirus-infected fibroblasts promotes cross-presentation of pp65 to CD8+ T cells.

An efficient host response to human cytomegalovirus (HCMV) infection may depend on rapid sensing of the infection by the innate immune response prior to deployment of viral immunosubversive functions. Control of HCMV dissemination could be ensured by apoptosis of cells immediately following infection. In the present report, it is demonstrated that changes in the ratio of c-FLIP to FLICE contributed to early sensitivity of HCMV-infected MRC5 fibroblasts to tumour necrosis factor alpha (TNF-alpha), providing an innate response to infection. Dendritic cells (DCs) co-cultured with HCMV-infected MRC5 cells acquired the ability to secrete TNF-alpha in an amount sufficient to kill infected fibroblasts. Blockage of TNF-alpha binding to its receptor on MRC5 cells with soluble TNF-R reduced the number of dead, HCMV-infected fibroblasts ingested by DCs, thus highlighting the impact of the apoptotic state of infected cells for efficient loading of DCs. Those DCs loaded with antigens available early in infection, such as input virion-associated pp65, could then engage antigen processing for cross-presentation to specific CD8(+) T cells. Cross-presentation was impaired when MRC5 cells were treated with the pan-caspase inhibitor ZVAD before co-culture with DCs. Altogether, our data suggest that the innate killing capacity of DCs at the early stage of infection plays a role in the activation of anti-HCMV CD8(+) T cells.

Age-related differences in sensitivity of peripheral blood monocytes to lipopolysaccharide and Staphylococcus aureus toxin B in atopic dermatitis.

As shown by atopy patch tests, atopic dermatitis (AD) is dominated in its acute phase by the development of a specific T(H)2 response after exposure of the skin to common environmental antigens. Relying on our previous data showing that Staphylococcus aureus enterotoxin B (SEB) induced the activation of monocyte-derived dendritic cells (DCs) through Toll-like receptor (TLR)2 and that SEB-pulsed DCs commit allogenic naive T cells into T(H)2, we assessed monocytes sensitivity to SEB and lipopolysaccharide (LPS) in a group of children and adult patients with AD. Monocytes from AD patients (15 adults with mostly severe disease and 15 children with mild to moderate disease) exhibited an activated and tolerant state as supported by (i) secretion of large amounts of IL-6, IL-10, and tumor necrosis factor-alpha even in the absence of stimulation; (ii) their inability to modulate neither HLA-DR and CD54 nor TLR2 and TLR4 expression after in vitro challenge with SEB; (iii) inhibition of IL-12p70 secretion in response to LPS. Interestingly, monocytes from some of the children studied responded to in vitro challenge with LPS, suggesting new hypotheses to explain disease regression. Our data support the notion that monitoring sensitivity of monocytes to bacterial toxins could prove useful to assess disease progression and prognosis in AD.

Activities of Z-ajoene against tumour and viral spreading in vitro.

Z-ajoene is a garlic-derived compound with known anti-tumour properties. This report argues in favour of pro-apoptotic and cell cycle blockage activities of Z-ajoene on various cell lines involving activation of the p53-family gene products, p53, p63 and p73, at indicated doses. According to its known anti-proteasome activity, Z-ajoene induced a downregulation of MHC-class I expression at the surface of treated cells but did not impair their recognition by CD8+ T cells. We further demonstrated a new activity of Z-ajoene against human cytomegalovirus spreading in vitro that was mediated by an increased number of apoptotic cells after infection. Altogether our data point at the ubiquitous efficiency of Z-ajoene as a new compound to fight against cancers of various origins including those that put up viruses.

Human dendritic cells conditioned with Staphylococcus aureus enterotoxin B promote TH2 cell polarization.

BACKGROUND: Immune surveillance against microbes at sites of interface with environment involves immediate recognition of pathogen-associated molecular patterns by dendritic cells (DCs). According to their first-line position, DCs are key parameters for the establishment of an appropriate innate and adaptive response against pathogens to avoid disease development. Even though their role in pathogenesis is well known, bacterial toxins have been less examined for their ability to drive DC activation and T-cell polarization. OBJECTIVE: We made the assumption that early conditioning of DCs with Staphylococcus aureus enterotoxins could take part in T-cell polarization. METHODS: Human monocyte-derived DCs were stimulated with S aureus enterotoxin B (SEB) and characterized with respect to secretion of inflammatory cytokines and their ability to drive polarization of naive allogenic T cells. RESULTS: We demonstrated that SEB induced maturation of DCs and that SEB-activated DCs secreted high levels of IL-2 but no IL-12p70, contrary to LPS-activated ones. Accordingly, we further showed that SEB-activated DCs were able to drive polarization of naive T cells into the T(H)2 subset. By using highly purified SEB and Toll-like receptor (TLR)-2 stably transfected Human Embryonic Kidney (HEK) 293 cells, we demonstrated for the first time the ability of SEB to induce TLR2 signaling. Furthermore, the involvement of SEB-TLR2 interaction in activation of dendritic cells was supported by neutralizing activity of anti-TLR2 antibodies. CONCLUSION: Altogether, our findings reinforce the notion that bacterial toxins may appear as new pathogen-associated molecular patterns, which could play a major role in inflammation and bacterial pathologies.