Vassili Soumelis

Human epithelial cells trigger dendritic cell–mediated allergic inflammation by producing TSLP

Whether epithelial cells play a role in triggering the immune cascade leading to T helper 2 (TH2)-type allergic inflammation is not known. We show here that human thymic stromal lymphopoietin (TSLP) potently activated CD11c+ dendritic cells (DCs) and induced production of the TH2-attracting chemokines TARC (thymus and activation-regulated chemokine; also known as CCL17) and MDC (macrophage-derived chemokine; CCL22). TSLP-activated DCs primed naïve TH cells to produce the proallergic cytokines interleukin 4 (IL-4), IL-5, IL-13 and tumor necrosis factor-α, while down-regulating IL-10 and interferon-γ. TSLP was highly expressed by epithelial cells, especially keratinocytes from patients with atopic dermatitis. TSLP expression was associated with Langerhans cell migration and activation in situ. These findings shed new light on the function of human TSLP and the role played by epithelial cells and DCs in initiating allergic inflammation.

A CRITICAL FUNCTION FOR TRANSFORMING GROWTH FACTOR-BETA, INTERLEUKIN 23 AND PROINFLAMMATORY CYTOKINES IN DRIVING AND MODULATING HUMAN T(H)-17 RESPONSES

Interleukin 17 (IL-17)–producing T helper 17 cells (TH-17 cells) have been described as a T helper cell subset distinct from T helper type 1 (TH1) and TH2 cells, with specific functions in antimicrobial defense and autoimmunity. The factors driving human TH-17 differentiation remain controversial. Using a systematic approach combining experimental and computational methods, we show here that transforming growth factor-β, interleukin 23 (IL-23) and proinflammatory cytokines (IL-1β and IL-6) were all essential for human TH-17 differentiation. However, individual TH-17 cell–derived cytokines, such as IL-17, IL-21, IL-22 and IL-6, as well as the global TH-17 cytokine profile, were differentially modulated by TH-17-promoting cytokines. Transforming growth factor-β was critical, and its absence induced a shift from a TH-17 profile to a TH1-like profile. Our results shed new light on the regulation of human TH-17 differentiation and provide a framework for the global analysis of T helper responses.

Dendritic cell lineage, plasticity and cross-regulation

Dendritic cells (DCs) are professional antigen-presenting cells that have an extraordinary capacity to stimulate naïve T cells and initiate primary immune responses. Here we review progress in understanding the additional functions of DCs in regulating the types of T cell–mediated immune responses and innate immunity to microbes. In addition, evidence for the existence of myeloid and lymphoid DC lineages and their different functions are summarized. We propose that the diverse functions of DCs in immune regulation are dictated by the instructions they received during innate immune responses to different pathogens and from their evolutionary lineage heritage.

Human thymic stromal lymphopoietin preferentially stimulates myeloid cells.

The sequence of a novel hemopoietic cytokine was discovered in a computational screen of genomic databases, and its homology to mouse thymic stromal lymphopoietin (TSLP) suggests that it is the human orthologue. Human TSLP is proposed to signal through a heterodimeric receptor complex that consists of a new member of the hemopoietin family termed human TSLP receptor and the IL-7R α-chain. Cells transfected with both receptor subunits proliferated in response to purified, recombinant human TSLP, with induced phosphorylation of Stat3 and Stat5. Human TSLPR and IL-7Rα are principally coexpressed on monocytes and dendritic cell populations and to a much lesser extent on various lymphoid cells. In accord, we find that human TSLP functions mainly on myeloid cells; it induces the release of T cell-attracting chemokines from monocytes and, in particular, enhances the maturation of CD11c+ dendritic cells, as evidenced by the strong induction of the costimulatory molecules CD40 and CD80 and the enhanced capacity to elicit proliferation of naive T cells.

TLR recognition of self nucleic acids hampers glucocorticoid activity in lupus

Glucocorticoids are widely used to treat patients with autoimmune diseases such as systemic lupus erythematosus (SLE). However, regimens used to treat many such conditions cannot maintain disease control in the majority of SLE patients and more aggressive approaches such as high-dose methylprednisolone pulse therapy are used to provide transient reductions in disease activity. The primary anti-inflammatory mechanism of glucocorticoids is thought to be NF-κB inhibition. Recognition of self nucleic acids by toll-like receptors TLR7 and TLR9 on B cells and plasmacytoid dendritic cells (PDCs) is an important step in the pathogenesis of SLE, promoting anti-nuclear antibodies and the production of type I interferon (IFN), both correlated with the severity of disease. Following their activation by self-nucleic acid-associated immune complexes, PDCs migrate to the tissues. We demonstrate, in vitro and in vivo, that stimulation of PDCs through TLR7 and 9 can account for the reduced activity of glucocorticoids to inhibit the IFN pathway in SLE patients and in two lupus-prone mouse strains. The triggering of PDCs through TLR7 and 9 by nucleic acid-containing immune complexes or by synthetic ligands activates the NF-κB pathway essential for PDC survival. Glucocorticoids do not affect NF-κB activation in PDCs, preventing glucocorticoid induction of PDC death and the consequent reduction of systemic IFN-α levels. These findings unveil a new role for self nucleic acid recognition by TLRs and indicate that inhibitors of TLR7 and 9 signalling could prove to be effective corticosteroid-sparing drugs.

Cutting Edge: Proinflammatory and Th2 Cytokines Synergize to Induce Thymic Stromal Lymphopoietin Production by Human Skin Keratinocytes

Thymic stromal lymphopoietin (TSLP) is an epithelial cell-derived cytokine that strongly activates dendritic cells (DC) and can initiate allergic inflammation. The factors inducing the production of human TSLP are not known. In this study, we show that proinflammatory (TNF-α or IL-1α) and Th2 (IL-4 or IL-13) cytokines synergized to induce the production of TSLP in human skin explants. TSLP production in situ was restricted to epidermal keratinocytes of the suprabasal layer. TSLP production could not be inhibited by factors regulating Th2 inflammation, such as IL-10, TGF-β, or IFN-γ. Cytokine-treated skin culture supernatants induced the maturation of blood CD11c+ DC in a TSLP-dependent manner. Our data provide the first evidence of TSLP induction and subsequent DC activation in human skin. Blocking TSLP-inducing cytokines could represent a novel strategy for the treatment of allergic diseases.

Characterization of resident and migratory dendritic cells in human lymph nodes

Human skin-draining lymph nodes contain functionally distinct subsets of resident and migratory dendritic cells.

A sensory neuron–expressed IL-31 receptor mediates T helper cell–dependent itch: Involvement of TRPV1 and TRPA1

BACKGROUND Although the cytokine IL-31 has been implicated in inflammatory and lymphoma-associated itch, the cellular basis for its pruritic action is yet unclear. OBJECTIVE We sought to determine whether immune cell-derived IL-31 directly stimulates sensory neurons and to identify the molecular basis of IL-31-induced itch. METHODS We used immunohistochemistry and quantitative real-time PCR to determine IL-31 expression levels in mice and human subjects. Immunohistochemistry, immunofluorescence, quantitative real-time PCR, in vivo pharmacology, Western blotting, single-cell calcium imaging, and electrophysiology were used to examine the distribution, functionality, and cellular basis of the neuronal IL-31 receptor α in mice and human subjects. RESULTS Among all immune and resident skin cells examined, IL-31 was predominantly produced by TH2 and, to a significantly lesser extent, mature dendritic cells. Cutaneous and intrathecal injections of IL-31 evoked intense itch, and its concentrations increased significantly in murine atopy-like dermatitis skin. Both human and mouse dorsal root ganglia neurons express IL-31RA, largely in neurons that coexpress transient receptor potential cation channel vanilloid subtype 1 (TRPV1). IL-31-induced itch was significantly reduced in TRPV1-deficient and transient receptor channel potential cation channel ankyrin subtype 1 (TRPA1)-deficient mice but not in c-kit or proteinase-activated receptor 2 mice. In cultured primary sensory neurons IL-31 triggered Ca(2+) release and extracellular signal-regulated kinase 1/2 phosphorylation, inhibition of which blocked IL-31 signaling in vitro and reduced IL-31-induced scratching in vivo. CONCLUSION IL-31RA is a functional receptor expressed by a small subpopulation of IL-31RA(+)/TRPV1(+)/TRPA1(+) neurons and is a critical neuroimmune link between TH2 cells and sensory nerves for the generation of T cell-mediated itch. Thus targeting neuronal IL-31RA might be effective in the management of TH2-mediated itch, including atopic dermatitis and cutaneous T-cell lymphoma.

Hepatitis C: viral and host factors associated with non-response to pegylated interferon plus ribavirin

Treatment for chronic hepatitis C virus (HCV) infection has evolved considerably in the last years. The standard of care (SOC) for HCV infection consists in the combination of pegylated interferon (PEG‐IFN) plus ribavirin. However, it only induces a sustained virological response (SVR) in half of genotype 1‐infected patients. Several viral and host factors have been associated with non‐response: steatosis, obesity, insulin resistance, age, male sex, ethnicity and genotypes. Many studies have demonstrated that in non‐responders, some interferon‐stimulated genes were upregulated before treatment. Those findings associated to clinical, biochemical and histological data may help detect responders before starting any treatment. This is a very important issue because the standard treatment is physically and economically demanding. The future of HCV treatment would probably consist in the addition of specifically targeted antiviral therapy for HCV such as protease and/or polymerase inhibitors to the SOC. In genotype 1 patients, very promising results have been reported when the protease inhibitor telaprevir or boceprevir is added to the SOC. It increases the SVR rates from approximately 50% (PEG‐IFN plus ribavirin) to 70% (for patients treated with a combination of PEG‐IFN plus ribavirin plus telaprevir). Different elements are associated with non‐response: (i) viral factors, (ii) host factors and (iii) molecular mechanisms induced by HCV proteins to inhibit the IFN signalling pathway. The goal of this review is to present the mechanisms of non‐response, to overcome it and to identify factors that can help to predict the response to anti‐HCV therapy.

Critical role of IL-21 in modulating TH17 and regulatory T cells in Behçet disease

BACKGROUND Behçet disease (BD) is a chronic systemic inflammatory disorder of unknown etiology. OBJECTIVE To determine the nature of T cells driving inflammatory lesions in BD. METHODS T cell homeostasis and cytokines production were analyzed in peripheral blood and brain inflammatory lesions from 45 adult patients with BD (active and untreated BD [n = 25] and patients in remission [n = 20]) and 20 healthy donors, using Luminex, flow cytometry, immunohistochemistry, and immunofluorescence analysis. RESULTS We found a marked increase in T(H)17 cells and a decrease in the frequency of CD4(+) forkhead box P3(+) regulatory T cells (Tregs) in peripheral blood that were induced by IL-21 production and that correlate with BD activity. The addition of serum from patients with active BD in a sorted CD4(+) T cells culture of healthy donors induced a significant and dose-dependent production of IL-17A and a decrease in forkhead box P3 expression. We demonstrated the presence of IL-21- and IL-17A-producing T cells within the cerebrospinal fluid, brain parenchyma inflammatory infiltrates, and intracerebral blood vessels from patients with active BD and central nervous system involvement. The stimulation of CD4(+) T cells with IL-21 increased T(H)17 and T(H)1 differentiation and decreased the frequency of Treg cells. Conversely, IL-21 blockade with an IL-21R-Fc restored the T(H)17 and Treg homeostasis in patients with BD. CONCLUSION We provided here the first evidence of the critical role of IL-21 in driving inflammatory lesions in BD by promoting T(H)17 effectors and suppressing Treg cells. IL-21 represents a promising target for novel therapy in BD.