Epidermal IL-15Rα acts as an endogenous antagonist of psoriasiform inflammation in mouse and man

Multi-System-Level Analysis Reveals Differential Expression of Stress Response-Associated Genes in Inflammatory Solar Lentigo

Although the pathogenesis of solar lentigo (SL) involves chronic ultraviolet (UV) exposure, cellular senescence, and upregulated melanogenesis, underlying molecular-level mechanisms associated with SL remain unclear. The aim of this study was to investigate the gene regulatory mechanisms intimately linked to inflammation in SL. Skin samples from patients with SL with or without histological inflammatory features were obtained. RNA-seq data from the samples were analyzed via multiple analysis approaches, including exploration of core inflammatory gene alterations, identifying functional pathways at both transcription and protein levels, comparison of inflammatory module (gene clusters) activation levels, and analyzing correlations between modules. These analyses disclosed specific core genes implicated in oxidative stress, especially the upregulation of nuclear factor kappa B in the inflammatory SLs, while genes associated with protective mechanisms, such as SLC6A9, were highly expressed in the non-inflammatory SLs. For inflammatory modules, Extracellular Immunity and Mitochondrial Innate Immunity were exclusively upregulated in the inflammatory SL. Analysis of protein-protein interactions revealed the significance of CXCR3 upregulation in the pathogenesis of inflammatory SL. In conclusion, the upregulation of stress response-associated genes and inflammatory pathways in response to UV-induced oxidative stress implies their involvement in the pathogenesis of inflammatory SL.

PCSK9 inhibition protects mice from food allergy

The Proprotein Convertase Subtilisin Kexin of type 9 (PCSK9) has been identified in 2003 as the third gene involved in familial hypercholesterolemia. PCSK9 binds to the membrane low-density lipoprotein receptor (LDLR) and promotes its cellular internalization and lysosomal degradation. Beyond this canonical role, PCSK9 was recently described to be involved in several immune responses. However, to date, the contribution of PCSK9 in food allergy remains unknown. Here, we showed that Pcsk9 deficiency or pharmacological inhibition of circulating PCSK9 with a specific monoclonal antibody (m-Ab) protected mice against symptoms of gliadin-induced-food allergy, such as increased intestinal transit time and ear oedema. Furthermore, specific PCSK9 inhibition during the elicitation steps of allergic process was sufficient to ensure anti-allergic effects in mice. Interestingly, the protective effect of PCSK9 inhibition against food allergy symptoms was independent of the LDLR as PCSK9 inhibitors remained effective in Ldlr deficient mice. In vitro, we showed that recombinant gain of function PCSK9 (PCSK9 D374Y) increased the percentage of mature bone marrow derived dendritic cells (BMDCs), promoted naïve T cell proliferation and potentiated the gliadin induced basophils degranulation. Altogether, our data demonstrate that PCSK9 inhibition is protective against gliadin induced food allergy in a LDLR-independent manner.

The therapeutic effect of glycyrrhizic acid compound ointment on imiquimod-induced psoriasis-like disease in mice

Glycyrrhetinic acid, a drug with anti-inflammatory effects, enhanced the activity of antipsoriatic efficacy. In this research, an ointment with glycyrrhetinic acid was prepaired as the major component and several other herbal monomers (astilbin, osthole, and momordin Ic) have antipsoriatic activity as minor components. Then an Imiquimod-induced psoriasis-like mouse model was established and the damaged skin condition of the administered group, the changes in the spleen index and the secretion of inflammatory factors in mouse skin were observed. Calcipotriol ointment was used as a positive control to compare the efficacy. Glycyrrhizic acid compound ointment significantly improved imiquimod-induced psoriasis in mice and reduced the secretion of TNF-α, IL-12, IL-17, and IL-23 in mouse skin, and showed a stronger therapeutic effect than calcipotriol ointment. Calcipotriol ointment did not significantly alleviate imiquimod-induced splenomegaly and did not significantly reduce the expression of IL-17 and IL-23 in mouse skin. Glycyrrhetinic acid compound ointment was more effective than calcipotriol and was dose-dependent in the treatment of imiquimod-induced psoriatic dermatitis in mice. Meanwhile,calcipotriol was not suitable for the treatment of Imiquimod -induced psoriasis-like mice.

Biased IL-2 signals induce Foxp3-rich pulmonary lymphoid structures and facilitate long-term lung allograft acceptance in mice

Transplantation of solid organs can be life-saving in patients with end-stage organ failure, however, graft rejection remains a major challenge. In this study, by pre-conditioning with interleukin-2 (IL-2)/anti-IL-2 antibody complex treatment biased toward IL-2 receptor α, we achieved acceptance of fully mismatched orthotopic lung allografts that remained morphologically and functionally intact for more than 90 days in immunocompetent mice. These allografts are tolerated by the actions of forkhead box p3 (Foxp3)⁺ regulatory T (Treg) cells that home to the lung allografts. Although counts of circulating Treg cells rapidly return to baseline following cessation of IL-2 treatment, Foxp3⁺ Treg cells persist in peribronchial and peribronchiolar areas of the grafted lungs, forming organized clusters reminiscent of inducible tertiary lymphoid structures (iTLS). These iTLS in lung allografts are made of Foxp3⁺ Treg cells, conventional T cells, and B cells, as evidenced by using microscopy-based distribution and neighborhood analyses. Foxp3-transgenic mice with inducible and selective deletion of Foxp3⁺ cells are unable to form iTLS in lung allografts, and these mice acutely reject lung allografts. Collectively, we report that short-term, high-intensity and biased IL-2 pre-conditioning facilitates acceptance of vascularized and ventilated lung allografts without the need of immunosuppression, by inducing Foxp3-controlled iTLS formation within allografts.

Counteracting Interleukin-15 to Elucidate Its Modes of Action in Physiology and Pathology

Interleukin (IL)-15 belongs to the common gamma-dependent cytokine family, along with IL-2, IL-4, IL-7, IL-9, and IL-21. IL-15 is crucial for the homeostasis of Natural Killer (NK) and memory CD8 T cells, and to fight against cancer progression. However, dysregulations of IL-15 expression could occur and participate in the emergence of autoimmune inflammatory diseases as well as hematological malignancies. It is therefore important to understand the different modes of action of IL-15 to decrease its harmful action in pathology without affecting its beneficial effects in the immune system. In this review, we present the different approaches used by researchers to inhibit the action of IL-15, from most broad to the most selective. Indeed, it appears that it is important to selectively target the mode of action of the cytokine rather than the cytokine itself as they are involved in numerous biological processes.

Interleukin 15 in murine models of colitis

Inflammatory bowel diseases (IBDs) are characterized by abnormal, non-antigen specific chronic inflammation of unknown etiology. Genome-wide association studies show that many IBD genetic susceptibility loci map to immune function genes and compelling evidence indicate that environmental factors play a critical role in IBD pathogenesis. Clinical and experimental evidence implicate the pro-inflammatory cytokine IL-15 in the pathogenesis of IBD. IL-15 and IL-15α expression is increased in the inflamed mucosa of IBD patients. IL-15 contributes to the maintenance of different cell subsets in the intestinal mucosa. However, very few studies have addressed the role of IL-15 in pre-clinical models of colitis. In this study, we use three well-characterized models of experimental colitis to determine the contribution of IL-15 to pathological intestinal inflammation.

Selective Targeting of IL-15Rα Is Sufficient to Reduce Inflammation

Cytokines are crucial molecules for maintaining the proper functioning of the immune system. Nevertheless, a dysregulation of cytokine expression could be involved in the pathogenesis of autoimmune diseases. Interleukin (IL)-15 is a key factor for natural killer cells (NK) and CD8 T cells homeostasis, necessary to fight cancer and infections but could also be considered as a pro-inflammatory cytokine involved in autoimmune inflammatory disease, including rheumatoid arthritis, psoriasis, along with tumor necrosis factor alpha (TNF-α), IL-6, and IL-1β. The molecular mechanisms by which IL-15 exerts its inflammatory function in these diseases are still unclear. In this study, we generated an IL-15-derived molecule called NANTIL-15 (New ANTagonist of IL-15), designed to selectively inhibit the action of IL-15 through the high-affinity trimeric IL-15Rα/IL-2Rβ/γc receptor while leaving IL-15 signaling through the dimeric IL-2Rβ/γc receptor unaffected. Administrating of NANTIL-15 in healthy mice did not affect the IL-15-dependent cell populations such as NK and CD8 T cells. In contrast, we found that NANTIL-15 efficiently reduced signs of inflammation in a collagen-induced arthritis model. These observations demonstrate that the inflammatory properties of IL-15 are linked to its action through the trimeric IL-15Rα/IL-2Rβ/γc receptor, highlighting the interest of selectively targeting this receptor.

Patients with systemic sclerosis show phenotypic and functional defects in neutrophils

BACKGROUND

Systemic sclerosis (SSc) is a multiorgan autoimmune disease characterized by inflammation, vascular modification, and progressive fibrosis of the skin and several visceral organs. Innate and adaptive immune cells, including myeloid, B and T cells, are believed to be central to the pathogenesis of SSc. However, the role and functional state of neutrophil granulocytes (neutrophils) are ill-defined in SSc.

METHODS

We performed a prospective study of neutrophils freshly isolated from SSc patients and healthy donors (HD) by measuring in these neutrophils (i) functional cell surface markers, including CD16, CD62L, CD66b, CD66c, CXCR1, CXCR2, and CXCR4; (ii) cytokine-activated intracellular signal transducer and activator of transcription (STAT) pathways, such as phosphorylated STAT3 (pSTAT3), pSTAT5, and pSTAT6; (iii) production of neutrophil extracellular traps (NET) and intracellular myeloperoxidase (MPO); and (iv) phagocytosis of bacteria by the neutrophils.

RESULTS

Neutrophils of SSc patients expressed lower CD16 and CD62L and higher pSTAT3 and pSTAT6 compared to HD. Moreover, neutrophils of SSc patients lacked CXCR1 and CXCR2, the receptors responding to the potent neutrophil chemoattractant CXCL8. Neutrophils of SSc patients were also deficient in MPO levels, NET formation, and phagocytosis of bacteria.

CONCLUSIONS

Neutrophils of patients with SSc display several functional defects affecting cell migration, NET formation, and phagocytosis of bacteria.

CCR7-guided neutrophil redirection to skin-draining lymph nodes regulates cutaneous inflammation and infection

Neutrophils are the first nonresident effector immune cells that migrate to a site of infection or inflammation; however, improper control of neutrophil responses can cause considerable tissue damage. Here, we found that neutrophil responses in inflamed or infected skin were regulated by CCR7-dependent migration and phagocytosis of neutrophils in draining lymph nodes (dLNs). In mouse models of Toll-like receptor-induced skin inflammation and cutaneous Staphylococcus aureus infection, neutrophils migrated from the skin to the dLNs via lymphatic vessels in a CCR7-mediated manner. In the dLNs, these neutrophils were phagocytosed by lymph node-resident type 1 and type 2 conventional dendritic cells. CCR7 up-regulation on neutrophils was a conserved mechanism across different tissues and was induced by a broad range of microbial stimuli. In the context of cutaneous immune responses, disruption of CCR7 interactions by selective CCR7 deficiency of neutrophils resulted in increased antistaphylococcal immunity and aggravated skin inflammation. Thus, neutrophil homing to and clearance in skin-dLNs affects cutaneous immunity versus pathology.

Soluble forms of cytokine and growth factor receptors: Mechanisms of generation and modes of action in the regulation of local and systemic inflammation

Cytokine and growth factor receptors are usually transmembrane proteins but they can also exist in soluble forms, either through cleavage and release of their ligand-binding extracellular domain, or through secretion of a soluble isoform. As an extension of this concept, transmembrane receptors on exosomes released into the circulation may act similarly to circulating soluble receptors. These soluble receptors add to the complexity of cytokine and growth factor signalling: they can function as decoy receptor that compete for ligand binding with their respective membrane-bound forms thereby attenuating signalling, or stabilize their ligands, or activate additional signalling events through interactions with other cell-surface proteins. Their soluble nature allows for a functional role away from the production sites, in remote cell types and organs. Accumulating evidence demonstrates that soluble receptors participate in the regulation and orchestration of various key cellular processes, particularly inflammatory responses. In this review, we will discuss release mechanisms of soluble cytokine and growth factor receptors, their mechanisms of action, as well as strategies for targeting their pathways in disease.

Inhibition of CtBP-Regulated Proinflammatory Gene Transcription Attenuates Psoriatic Skin Inflammation

Psoriasis is a chronic immune-mediated disease characterized by excessive proliferation of epidermal keratinocytes and increased immune cell infiltration to the skin. Although it is well-known that psoriasis pathogenesis is driven by aberrant production of proinflammatory cytokines, the mechanisms underlying the imbalance between proinflammatory and anti-inflammatory cytokine expression are incompletely understood. In this study, we report that the transcriptional coregulators CtBP1 and 2 can transactivate a common set of proinflammatory genes both in the skin of imiquimod-induced mouse psoriasis model and in human keratinocytes and macrophages stimulated by imiquimod. We find that mice overexpressing CtBP1 in epidermal keratinocytes display severe skin inflammation phenotypes with increased expression of T helper type 1 and T helper type 17 cytokines. We also find that the expression of CtBPs and CtBP-target genes is elevated both in human psoriatic lesions and in the mouse imiquimod psoriasis model. Moreover, we were able to show that topical treatment with a peptidic inhibitor of CtBP effectively suppresses the CtBP-regulated proinflammatory gene expression and thus attenuates psoriatic inflammation in the imiquimod mouse model. Together, our findings suggest to our knowledge previously unreported strategies for therapeutic modulation of the immune response in inflammatory skin diseases.

IL-15Rα-Independent IL-15 Signaling in Non-NK Cell-Derived IFNγ Driven Control of Listeria monocytogenes

Interleukin-15, produced by hematopoietic and parenchymal cells, maintains immune cell homeostasis and facilitates activation of lymphoid and myeloid cell subsets. IL-15 interacts with the ligand-binding receptor chain IL-15Rα during biosynthesis, and the IL-15:IL-15Rα complex is trans-presented to responder cells that express the IL-2/15Rβγ_c complex to initiate signaling. IL-15-deficient and IL-15Rα-deficient mice display similar alterations in immune cell subsets. Thus, the trimeric IL-15Rαβγ_c complex is considered the functional IL-15 receptor. However, studies on the pathogenic role of IL-15 in inflammatory and autoimmune diseases indicate that IL-15 can signal independently of IL-15Rα via the IL-15Rβγ_c dimer. Here, we compared the ability of mice lacking IL-15 (no signaling) or IL-15Rα (partial/distinct signaling) to control Listeria monocytogenes infection. We show that IL-15-deficient mice succumb to infection whereas IL-15Rα-deficient mice clear the pathogen as efficiently as wildtype mice. IL-15-deficient macrophages did not show any defect in bacterial uptake or iNOS expression in vitro. In vivo, IL-15 deficiency impaired the accumulation of inflammatory monocytes in infected spleens without affecting chemokine and pro-inflammatory cytokine production. The inability of IL-15-deficient mice to clear L. monocytogenes results from impaired early IFNγ production, which was not affected in IL-15Rα-deficient mice. Administration of IFNγ partially enabled IL-15-deficient mice to control the infection. Bone marrow chimeras revealed that IL-15 needed for early bacterial control can originate from both hematopoietic and non-hematopoietic cells. Overall, our findings indicate that IL-15-dependent IL-15Rα-independent signaling via the IL-15Rβγ_c dimeric complex is necessary and sufficient for the induction of IFNγ from sources other than NK/NKT cells to control bacterial pathogens.

Rational modification, synthesis and biological evaluation of N-substituted phthalazinone derivatives designed to target interleukine-15 protein

Interleukin (IL)-15 is a pleiotropic cytokine structurally close to IL-2 and sharing with the IL-2Rβ and γc receptor (R) subunits. IL-15 plays important roles in innate and adaptative immunity, supporting the activation and proliferation of NK, NK-T, and CD8⁺ T cells. Over-expression of IL-15 has been shown to participate to the development of inflammatory and autoimmune diseases and diverse T cell malignancies. This study is in continuity of our previous work through which a family of small-molecule inhibitors impeding IL-15/IL-2Rβ interaction with sub-micromolar activity has been identified using pharmacophore-based virtual screening and hit optimization methods. With the aim to improve the efficacy and selectivity of our lead inhibitor, specific modifications have been introduced on the basis of optimized SAR and modelisation. The new series of compounds generated have been evaluated for their capacity to inhibit the proliferation as well as the down-stream signaling of IL-15-dependent cells and to bind to IL-15.

Interleukin-15 enhances proinflammatory T-cell responses in patients with MS and EAE

Objective

We posit that interleukin-15 (IL-15) is a relevant contributor to MS pathobiology as this cytokine is elevated in the CNS and periphery of patients with MS. We aim to investigate (1) the impact of IL-15 on T lymphocytes from patients with MS and (2) the in vivo role of IL-15 using the experimental autoimmune encephalomyelitis (EAE) mouse model.

Methods

We compared the impact of IL-15 on T lymphocytes obtained from untreated patients with MS (relapsing-remitting, secondary progressive, and primary progressive) to cells from age/sex-matched healthy controls (HCs) using multiparametric flow cytometry and in vitro assays. We tested the effects of peripheral IL-15 administration after EAE disease onset in C57BL/6 mice.

Results

IL-15 triggered STAT5 signaling in an elevated proportion of T cells from patients with MS compared with HCs. This cytokine also enhanced the production of key proinflammatory cytokines (interferon γ, granulocyte-macrophage colony-stimulating factor [GM-CSF], IL-17, and tumor necrosis factor) by T cells from both MS and controls, but these effects were more robust for the production of IL-17 and GM-CSF in T-cell subsets from patients with MS. At the peak of EAE disease, the proportion of CD4⁺ and CD8⁺ T cells expressing CD122⁺, the key signaling IL-15 receptor chain, was enriched in the CNS compared with the spleen. Finally, peripheral administration of IL-15 into EAE mice after disease onset significantly aggravated clinical scores and increased the number of inflammatory CNS-infiltrating T cells long term after stopping IL-15 administration.

Conclusions

Our results underscore that IL-15 contributes to the amplification of T-cell inflammatory properties after disease onset in both MS and EAE.

Cytokinocytes: the diverse contribution of keratinocytes to immune responses in skin

The skin serves as the primary interface between our body and the external environment and acts as a barrier against entry of physical agents, chemicals, and microbes. Keratinocytes make up the main cellular constitute of the outermost layer of the skin, contributing to the formation of the epidermis, and they are crucial for maintaining the integrity of this barrier. Beyond serving as a physical barrier component, keratinocytes actively participate in maintaining tissue homeostasis, shaping, amplifying, and regulating immune responses in skin. Keratinocytes act as sentinels, continuously monitoring changes in the environment, and, through microbial sensing, stretch, or other physical stimuli, can initiate a broad range of inflammatory responses via secretion of various cytokines, chemokines, and growth factors. This diverse function of keratinocytes contributes to the highly variable clinical manifestation of skin immune responses. In this Review, we highlight the highly diverse functions of epidermal keratinocytes and their contribution to various immune-mediated skin diseases.

Interleukin-15 in autoimmunity

Interleukin-15 (IL-15) is a member of the IL-2 family of cytokines, which use receptor complexes containing the common gamma (γ_c) chain for signaling. IL-15 plays important roles in innate and adaptative immune responses and is implicated in the pathogenesis of several immune diseases. The IL-15 receptor consists of 3 subunits namely, the ligand-binding IL-15Rα chain, the β chain (also used by IL-2) and the γ_c chain. IL-15 uses a unique signaling pathway whereby IL-15 associates with IL-15Rα during biosynthesis, and this complex is 'trans-presented' to responder cells that expresses the IL-2/15Rβγ_c receptor complex. IL-15 is subject to post-transcriptional and post-translational regulation, and evidence also suggests that IL-15 cis-signaling can occur under certain conditions. IL-15 has been implicated in the pathology of various autoimmune diseases such as rheumatoid arthritis, autoimmune diabetes, inflammatory bowel disease, coeliac disease and psoriasis. Studies with pre-clinical models have shown the beneficial effects of targeting IL-15 signaling in autoimmunity. Unlike therapies targeting other cytokines, anti-IL-15 therapies have not yet been successful in humans. We discuss the complexities of IL-15 signaling in autoimmunity and explore potential immunotherapeutic approaches to target the IL-15 signaling pathway.

Dihydroartemisinin ameliorates psoriatic skin inflammation and its relapse by diminishing CD8+ T-cell memory in wild-type and humanized mice

Conventional immunosuppressants cause side effects and do not prevent the recurrence of autoimmune diseases. Moreover, they may not inhibit autoimmunity mediated by pathogenic memory T-cells. Dihydroartemisinin (DHA) has been shown to regulate autoimmunity. However, it remains unknown whether DHA impacts psoriasis and its recurrence. The objective of this study was to determine therapeutic effects of DHA on psoriasis and its relapse as well as its underlying mechanisms.

Methods: We established animal models of imiquimod (IMQ)-induced psoriasis-like wild-type mice and humanized NSG mice receiving lesional human skin from patients with psoriasis. Many immunoassays, including immunohistochemistry, flow cytometry, quantitative RT-PCR and Western blotting, were performed.

Results: We found that DHA not only ameliorated acute skin lesion of psoriatic mice, but also alleviated its recurrence by diminishing CD8⁺ central memory T (T_CM) and CD8⁺ resident memory T (T_RM) cells. It attenuated epidermal pathology and T-cell infiltration in the skin of IMQ-induced psoriatic mice while suppressing expression of IL-15, IL-17 and other proinflammatory cytokines in the skin. Surprisingly, DHA reduced the frequency and number of CD8⁺, but not CD4⁺, subset of CD44^highCD62L^high T_CM in psoriatic mice, whereas methotrexate (MTX) lowered CD4⁺, but not CD8⁺, T_CM frequency and number. Indeed, DHA, but not MTX, downregulated eomesodermin (EOMES) and BCL-6 expression in CD8⁺ T-cells. Furthermore, DHA, but not MTX, reduced the presence of CD8⁺CLA⁺, CD8⁺CD69⁺ or CD8⁺CD103⁺ T_RM cells in mouse skin. Interestingly, treatment with DHA, but not MTX, during the first onset of psoriasis largely prevented psoriasis relapse induced by low doses of IMQ two weeks later. Administration of recombinant IL-15 or CD8⁺, but not CD4⁺, T_CM cells resulted in complete recurrence of psoriasis in mice previously treated with DHA. Finally, we demonstrated that DHA alleviated psoriatic human skin lesions in humanized NSG mice grafted with lesional skin from psoriatic patients while reducing human CD8⁺ T_CM and CD103⁺ T_RM cells in humanized mice.

Conclusion: We have provided the first evidence that DHA is advantageous over MTX in preventing psoriasis relapse by reducing memory CD8⁺ T-cells.

Interleukin-15 (dys)regulation of lymphoid homeostasis: Implications for therapy of autoimmunity and cancer

IL-15 supports NK, NK-T, γδ, ILC1, and memory CD8 T cell function, and dysregulated IL-15 is associated with many autoimmune diseases. Striking IL-15–driven increases in NK and CD8 T cells in patients highlight the potential for combination therapy of cancers.

IL-15, a pleiotropic cytokine, stimulates generation of NK, NK-T, γδ, ILC1, and memory CD8 T cells. IL-15 disorders play pathogenetic roles in organ-specific autoimmune diseases including celiac disease. Diverse approaches are developed to block IL-15 action. IL-15 administered to patients with malignancy yielded dramatic increases in NK numbers and modest increases in CD8 T cells. Due to immunological checkpoints, to achieve major cancer therapeutic efficacy, IL-15 will be used in combination therapy, and combination trials with checkpoint inhibitors, with anti-CD40 to yield tumor-specific CD8 T cells, and with anticancer monoclonal antibodies to increase ADCC and antitumor efficacy, have been initiated.

IL-15 and IL-23 synergize to trigger Th17 response by CLA+ T cells in psoriasis

IL-15 has emerged as a potentially relevant target in the IL-17 response in psoriasis. However, its mechanism is poorly characterized in humans. IL-15 and IL-23 are constitutively expressed in the psoriatic lesion. Also, IL-15 is considered a susceptibility-associated gene in psoriasis, as are IL-23R, and HLACW6. Here, we studied the effect of IL-15 and IL-23 stimulation on the cytokine response of CLA+/CLA- T cells from 9 psoriasis patients and 3 healthy control subjects. To this end, CLA + and CLA- T cells from blood samples were cultured with epidermal cells from skin biopsies and treated with IL-15 and IL-23. After five days of culture, cytokines in supernatant were measured by ELISA or fluorescent bead-based immunoassay. There was a statistically significant increase in IL-17F and IL-17A production (P < .001) in cocultures of psoriasis skin-homing CLA + T cells with epidermal cells when stimulated with IL-15 and IL-23, but this effect was not observed in the cells of healthy controls. Interestingly, this response was reduced by around 50 to 80% by blocking HLA class I and II molecules. Our results point to the synergic action of IL-15 and IL-23 selectively for CLA + cells in psoriasis, leading to the induction of Th17 cell-related cytokines.

Biological functions and therapeutic opportunities of soluble cytokine receptors

Cytokines control the immune system by regulating the proliferation, differentiation and function of immune cells. They activate their target cells through binding to specific receptors, which either are transmembrane proteins or attached to the cell-surface via a GPI-anchor. Different tissues and individual cell types have unique expression profiles of cytokine receptors, and consequently this expression pattern dictates to which cytokines a given cell can respond. Furthermore, soluble variants of several cytokine receptors exist, which are generated by different molecular mechanisms, namely differential mRNA splicing, proteolytic cleavage of the membrane-tethered precursors, and release on extracellular vesicles. These soluble receptors shape the function of cytokines in different ways: they can serve as antagonistic decoy receptors which compete with their membrane-bound counterparts for the ligand, or they can form functional receptor/cytokine complexes which act as agonists and can even activate cells that would usually not respond to the ligand alone. In this review, we focus on the IL-2 and IL-6 families of cytokines and the so-called Th2 cytokines. We summarize for each cytokine which soluble receptors exist, were they originate from, how they are generated, and what their biological functions are. Furthermore, we give an outlook on how these soluble receptors can be exploited for therapeutic purposes.

Natural killer cells get under your skin

Natural killer cells collaborate with type 2 immune cells to modulate atopic dermatitis pathogenesis (Mack et al, this issue).

The IL-15 / sIL-15Rα complex modulates immunity without effect on asthma features in mouse

BACKGROUND

Interleukin 15 (IL-15) is a growth and modulating factor for B, T lymphocytes and natural killer cells (NK). Its action on innate and adaptive immunity is modulated by its alpha chain receptor (IL-15Rα). The IL-15/sIL-15Rα complex (IL-15Cx) increases the bioavailability and activity of the cytokine in vivo. IL-15Cx has been used in diseases to dampen IL-15 inflammation by the use of soluble IL-15Ralpha specificity. Here, we aim to evaluate the interest of IL-15Cx in a mouse model of asthma.

METHODS

Using a mouse model of asthma consisting in percutaneous sensitization and intranasal challenge with total house dust mite extract, we evaluated the effect of IL-15Cx injected intraperitoneally four times after a first nasal challenge. Respiratory function was assessed by the technique of forced oscillations (Flexivent®). The effect on bronchial remodeling was evaluated by lung histology. The inflammatory status was analyzed by flow cytometry.

RESULTS

We observed that the IL-15Cx modulates lung and systemic inflammation by increasing NK cells, CD8⁺ memory T cells and regulatory cells. However, IL-15Cx displays no effect on bronchial hyperreactivity, bronchial remodeling nor cellular bronchial infiltrate, but limits the secretion of bronchial mucus and modulates only inflammatory response in a HDM-allergic asthma murine model.

CONCLUSIONS

IL-15Cx has a limited effect on immune response in asthma and has no effect on lung function in mice. Thus, it limits its therapeutic potential but might suggest a combinatory potential with other therapeutics.

Keratinocyte-derived IκBζ drives psoriasis and associated systemic inflammation

The transcriptional activator IκBζ is a key regulator of psoriasis, but which cells mediate its pathogenic effect remains unknown. Here we found that IκBζ expression in keratinocytes triggers not only skin lesions but also systemic inflammation in mouse psoriasis models. Specific depletion of IκBζ in keratinocytes was sufficient to suppress the induction of imiquimod- or IL-36–mediated psoriasis. Moreover, IκBζ ablation in keratinocytes prevented the onset of psoriatic lesions and systemic inflammation in keratinocyte-specific IL-17A–transgenic mice. Mechanistically, this psoriasis protection was mediated by IκBζ deficiency in keratinocytes abrogating the induction of specific proinflammatory target genes, including Cxcl5, Cxcl2, Csf2, and Csf3, in response to IL-17A or IL-36. These IκBζ-dependent genes trigger the generation and recruitment of neutrophils and monocytes that are needed for skin inflammation. Consequently, our data uncover a surprisingly pivotal role of keratinocytes and keratinocyte-derived IκBζ as key mediators of psoriasis and psoriasis-related systemic inflammation.

Deletion of IκBζ in keratinocytes is sufficient to abrogate psoriasis induction in mouse models due to changes in transcription of keratinocyte-derived chemo- and cytokines.

Nanoparticle-Coupled Topical Methotrexate Can Normalize Immune Responses and Induce Tissue Remodeling in Psoriasis

Methotrexate (MTX) is an antiproliferative drug used for treating inflammatory diseases, including psoriasis. Nevertheless, its use in localized therapy is hindered because of poor transdermal penetration. We show that MTX coupled with gold nanoparticles (GNPs) demonstrates superior antiinflammatory efficacy than MTX alone in an imiquimod-induced mouse model, significantly reducing γδ T cells, CD4⁺ T cells, and neutrophils. Furthermore, it was well tolerated upon systemic and topical administration. In an AGR129 human xenograft mouse model, two-week topical treatment with MTX-GNPs inhibited skin hyperplasia significantly better than topical calcipotriol-betamethasone and led to profound tissue remodeling, involving the upregulation of extracellular matrix reorganization and the downregulation of cornification and keratinization processes. The number of resident T cells in the grafts, as well as interleukin-17 production, drastically decreased upon MTX-GNP treatment. While both MTX and MTX-GNPs directly prevented the proliferation and induced apoptosis of T cells, the suppression of cytokine production was a shared mechanism of GNP and MTX-GNPs. In conclusion, MTX-GNPs influence immune and stromal components of the skin, leading to the potent inhibition of pathogenesis in preclinical psoriasis. MTX-GNPs surpass the efficacy of conventional MTX and standard of care, emerging as a non-steroidal, topical alternative for psoriasis treatment.

Geraniol targets KV1.3 ion channel and exhibits anti-inflammatory activity in vitro and in vivo

Naturally occurring monoterpenes are known for their various pharmacological activities including anti-inflammation. K_V1.3 ion channel is a voltage-gated potassium channel and has been validated as a drug target for autoimmune and chronic inflammatory diseases like psoriasis. Here we experimentally test the direct interaction between monoterpenes and K_V1.3 ion channel. Our electrophysiological analysis determined that monoterpenes (geraniol, nerol, β-citronellol, citral and linalool) have inhibitory effects on K_V1.3 ion channel. Representatively, geraniol reversibly blocked K_V1.3 currents in a voltage-dependent manner with an IC₅₀ of 490.50 ± 1.04 μM at +40 mV in HEK293T cells. At the effective concentrations, geraniol also inhibited cytokine secretion of activated human T cells, including IL-2, TNF-α and IFN-γ. In an imiquimod-induced psoriasis-like animal model, geraniol administration significantly reduced psoriasis area and severity index scores, ameliorated the deteriorating histopathology and decreased the degree of splenomegaly. Together, our findings not only suggest that monoterpenes may serve as lead molecules for the development of K_V1.3 inhibitors, but also indicate that geraniol could be considered as a promising therapeutic candidate to treat autoimmune diseases.

Salvia mellifera-How Does It Alleviate Chronic Pain?

Black sage, Salvia mellifera, can be made into a sun tea that is used as a foot soak to treat pain patients. The monoterpenoids and diterpenoids in the preparation penetrate the skin of the feet and stop the pain chemokine cycle, which may be the basis of chronic pain. Several chronic pain patients have reported long-term improvements in their pain after treatment with the preparation.

Tissue maintenance of CMV-specific inflationary memory T cells by IL-15

Cytomegalovirus (CMV) infection induces an atypical CD8 T cell response, termed inflationary, that is characterised by accumulation and maintenance of high numbers of effector memory like cells in circulation and peripheral tissues—a feature being successfully harnessed for vaccine purposes. Although stability of this population depends on recurrent antigen encounter, the requirements for prolonged survival in peripheral tissues remain unknown. Here, we reveal that murine CMV-specific inflationary CD8 T cells are maintained in an antigen-independent manner and have a half-life of 12 weeks in the lung tissue. This half-life is drastically longer than the one of phenotypically comparable inflationary effector cells. IL-15 alone, and none of other common γ-cytokines, was crucial for survival of inflationary cells in peripheral organs. IL-15, mainly produced by non-hematopoietic cells in lung tissue and being trans-presented, promoted inflationary T cell survival by increasing expression of Bcl-2. These results indicate that inflationary CD8 T cells are not just simply effector-like cells, rather they share properties of both effector and memory CD8 T cells and they appear to be long-lived cells compared to the effector cells from acute virus infections.

A majority of the human population is infected with cytomegalovirus (CMV), which results in lifelong persistence due to viral latency. CMV induces remarkably strong and sustained effector memory-like CD8 T cell responses in circulation and peripheral tissues, also referred to as memory CD8 T cell "inflation". In tissues, these effector memory-like cells contribute to immunosurveillance and early control of CMV reactivation events. Due to the high numbers and effector-like functional properties of inflationary CD8 T cells in peripheral tissues, CMV-based vectors are gaining substantial interest in the context of T cell based vaccines that protect peripheral tissues against infections or tumors. Here, we investigated how the stable peripheral pool of inflationary CD8 T cells is maintained and show that inflationary CD8 T cells are long-lived T cells and have a markedly prolonged half-life compared to effector CD8 T cells. In peripheral organs such as lung, IL-15 cytokine is pivotal in promoting maintenance of inflationary cells by inducing expression of the anti-apoptotic molecule Bcl-2. We show that IL-15 is mainly expressed by non-hematopoietic cells in lung tissue and that IL-15 is trans-presented to the inflationary CD8 T cells in vivo. Thus, CMV-driven inflationary CD8 T cell responses represent a unique T cell subset in peripheral tissues that is regulated differently compared to T_RM CD8 T cells emerging after vaccination or acute infections.

Frequencies of IL-15Rα+ cells in patients with Behçet's disease and the effects of overexpressing IL-15Rα+ on disease symptoms in mice

It has been suggested higher serum levels of IL-15 and lower expression levels of IL-15 receptor alpha (IL-15Rα) are correlated with pathogenesis of Behçet's disease (BD). However, whether overexpressing IL-15Rα could be used as a therapeutic candidate for BD is currently unclear. Therefore, the purpose of this study was to determine whether overexpressing IL-15Rα could affect BD symptoms in a mouse model. IL-15/IL-15Rα complex expressing vector or protein complex of IL-15/IL-15Rα-Fc was used to treat BD mice. Frequencies of IL-15Rα+ cells in peripheral blood leukocytes (PBL) and lymph node cells were determined using a flow cytometer. BD symptoms in mice improved after treatment with IL-15/15Rα expression vector or IL-15/IL-15Rα-Fc protein complex. In addition, treatment with pIL-15/15Rα significantly (p = .016) decreased disease severity score of BD mice compared to treatment with control vector. Frequencies of IL-15Rα+ cells were also significantly (p = .01) higher in peritoneal macrophages of pIL-15/15Rα treated BD mice than those of mice treated with control vector. Frequencies of IL-15Rα+ PBL were also significantly higher in BD mice treated with IL-15/IL-15Rα-Fc protein complex than those in the control group. These results suggest up-regulating IL-15Rα+ cells could be used as novel therapeutic strategies to control BD in the future.

Topical administration of reversible SAHH inhibitor ameliorates imiquimod-induced psoriasis-like skin lesions in mice via suppression of TNF-α/IFN-γ-induced inflammatory response in keratinocytes and T cell-derived IL-17

DZ2002, a reversible S-adenosyl-l-homocysteine hydrolase (SAHH) inhibitor with immunosuppressive properties and potent therapeutic activity against various autoimmune diseases in mice. The present study was designed to characterize the potential therapeutic effects of DZ2002 on murine model of psoriasis and reveal the correlated mechanisms. In this report, we demonstrated that in vitro, DZ2002 significantly decreased the expression of pro-inflammatory cytokines and adhesion molecule including IL-1α, IL-1β, IL-6, IL-8, TNF-α and ICAM-1 by inhibiting the phosphorylation of p38 MAPK, ERK and JNK in TNF-α/IFN-γ-stimulated HaCaT human keratinocytes. Topical administration of DZ2002 alleviated the imiquimod (IMQ)-induced psoriasis-like skin lesions and inflammation in mice, the therapeutic effect was comparable with the Calcipotriol. Moreover, the inflammatory skin disorder was restored by DZ2002 treatment characterized by reducing both of the CD3⁺ T cell accumulation and the psoriasis-specific cytokines expression. Further, we found that DZ2002 improved IMQ-induced splenomegaly and decreased the frequency of splenic IL-17-producing T cells. Our finding offered the convincing evidence that SAHH inhibitor DZ2002 might attenuate psoriasis by simultaneously interfering the abnormal activation and differentiation of keratinocytes and accumulation of IL-17-producing T cells in skin lesions.

Characterization of Receptor-Associated Protein Complex Assembly in Interleukin (IL)-2- and IL-15-Activated T-Cell Lines

It remains a paradox that IL-2 and IL-15 can differentially modulate the immune response using the same signaling receptors. We have previously dissected the phosphotyrosine-driven signaling cascades triggered by both cytokines in Kit225 T-cells, unveiling subtle differences that may contribute to their functional dichotomy. In this study, we aimed to decipher the receptor complex assembly in IL-2- and IL-15-activated T-lymphocytes that is highly orchestrated by site-specific phosphorylation events. Comparing the cytokine-induced interactome of the interleukin receptor beta and gamma subunits shared by the two cytokines, we defined the components of the early IL-2 and IL-15 receptor-associated complex discovering novel constituents. Additionally, phosphopeptide-directed analysis allowed us to detect several cytokine-dependent and -independent phosphorylation events within the activated receptor complex including novel phosphorylated sites located in the cytoplasmic region of IL-2 receptor β subunit (IL-2Rβ). We proved that the distinct phosphorylations induced by the cytokines serve for recruiting different types of effectors to the initial receptor/ligand complex. Overall, our study sheds new light into the initial molecular events triggered by IL-2 and IL-15 and constitutes a further step toward a better understanding of the early signaling aspects of the two closely related cytokines in T-lymphocytes.

IL-12 protects from psoriasiform skin inflammation

Neutralization of the common p40-subunit of IL-12/23 in psoriasis patients has led to a breakthrough in the management of moderate to severe disease. Aside from neutralizing IL-23, which is thought to be responsible for the curative effect, anti-p40 therapy also interferes with IL-12 signalling and type 1 immunity. Here we dissect the individual contribution of these two cytokines to the formation of psoriatic lesions and understand the effect of therapeutic co-targeting of IL-12 and IL-23 in psoriasis. Using a preclinical model for psoriatic plaque formation we show that IL-12, in contrast to IL-23, has a regulatory function by restraining the invasion of an IL-17-committed γδT (γδT17) cell subset. We discover that IL-12 receptor signalling in keratinocytes initiates a protective transcriptional programme that limits skin inflammation, suggesting that collateral targeting of IL-12 by anti-p40 monoclonal antibodies is counterproductive in the therapy of psoriasis.

Recent advances in understanding psoriasis

T helper (Th) cells producing interleukin (IL)-17, IL-22, and tumor necrosis factor (TNF) form the key T cell population driving psoriasis pathogenesis. They orchestrate the inflammation in the skin that results in the proliferation of keratinocytes and endothelial cells. Besides Th17 cells, other immune cells that are capable of producing IL-17-associated cytokines participate in psoriatic inflammation. Recent advances in psoriasis research improved our understanding of the cellular and molecular players that are involved in Th17 pathology and inflammatory pathways in the skin. The inflammation-driving actions of TNF in psoriasis are already well known and antibodies against TNF are successful in the treatment of Th17-mediated psoriatic skin inflammation. A further key cytokine with potent IL-17-/IL-22-promoting properties is IL-23. Therapeutics directly neutralizing IL-23 or IL-17 itself are now extending the therapeutic spectrum of antipsoriatic agents and further developments are on the way. The enormous progress in psoriasis research allows us to control this Th17-mediated inflammatory skin disease in many patients.

IL-17 receptor A and adenosine deaminase 2 deficiency in siblings with recurrent infections and chronic inflammation

BACKGROUND

Data on patients affected by chronic mucocutaneous candidiasis underscore the preponderant role of IL-17 receptor A (IL-17RA) in preserving mucocutaneous immunity. Little is known about the role of adenosine deaminase (ADA) 2 in regulation of immune responses, although recent reports linked ADA2 deficiency with inflammation and vasculitis.

OBJECTIVE

We sought to investigate the mechanisms of chronic inflammation and vasculitis in a child lacking IL-17RA and ADA2 to identify therapeutic targets.

METHODS

We report a family with 2 siblings who have had recurrent mucocutaneous infections with Candida albicans and Staphylococcus aureus and chronic inflammatory disease and vasculitis since early childhood, which were refractory to classical treatments. Array-based comparative genomic hybridization analysis showed that both siblings are homozygous for a 770-kb deletion on chr22q11.1 encompassing both IL17RA and cat eye critical region 1 (CECR1). Immunologic studies were carried out by means of flow cytometry, ELISA, and RIA.

RESULTS

As expected, in the affected child we found a lack of IL-17RA expression, which implies a severe malfunction in the IL-17 signaling pathway, conferring susceptibility to recurrent mucocutaneous infections. Surprisingly, we detected an in vitro and in vivo upregulation of proinflammatory cytokines, notably IL-1β and TNF-α, which is consistent with the persistent systemic inflammation.

CONCLUSIONS

This work emphasizes the utility of whole-genome analyses combined with immunologic investigation in patients with unresolved immunodeficiency. This approach is likely to provide an insight into immunologic pathways and mechanisms of disease. It also provides molecular evidence for more targeted therapies. In addition, our report further corroborates a potential role of ADA2 in modulating immunity and inflammation.

IL-15 functions as a danger signal to regulate tissue-resident T cells and tissue destruction

In this Opinion article, we discuss the function of tissues as a crucial checkpoint for the regulation of effector T cell responses, and the notion that interleukin-15 (IL-15) functions as a danger molecule that communicates to the immune system that the tissue is under attack and poises it to mediate tissue destruction. More specifically, we propose that expression of IL-15 in tissues promotes T helper 1 cell-mediated immunity and provides co-stimulatory signals to effector cytotoxic T cells to exert their effector functions and drive tissue destruction. Therefore, we think that IL-15 contributes to tissue protection by promoting the elimination of infected cells but that when its expression is chronically dysregulated, it can promote the development of complex T cell-mediated disorders associated with tissue destruction, such as coeliac disease and type 1 diabetes.

Human fused NKG2D-IL-15 protein controls xenografted human gastric cancer through the recruitment and activation of NK cells

Interleukin (IL)-15 plays an important role in natural killer (NK) and CD8+ T-cell proliferation and function and is more effective than IL-2 for tumor immunotherapy. The trans-presentation of IL-15 by neighboring cells is more effective for NK cell activation than its soluble IL-15. In this study, the fusion protein dsNKG2D-IL-15, which consisted of two identical extracellular domains of human NKG2D coupled to human IL-15 via a linker, was engineered in Escherichia coli. DsNKG2D-IL-15 could efficiently bind to major histocompatibility complex class I chain-related protein A (MICA) of human tumor cells with the two NKG2D domains and trans-present IL-15 to NK or CD8+ T cells. We transplanted human gastric cancer (SGC-7901) cells into nude mice and mouse melanoma cells with ectopic expression of MICA (B16BL6-MICA) into C57BL/6 mice. Then, we studied the anti-tumor effects mediated by dsNKG2D-IL-15 in the two xenografted tumor models. Human dsNKG2D-IL-15 exhibited higher efficiency than IL-15 in suppressing gastric cancer growth. Exogenous human dsNKG2D-IL-15 was centrally distributed in the mouse tumor tissues based on in vivo live imaging. The frequencies of human CD56+ cells infiltrated into the tumor tissues following the injection of peripheral blood mononuclear cells into nude mice bearing human gastric cancer were significantly increased by human dsNKG2D-IL-15 treatment. Human dsNKG2D-IL-15 also delayed the growth of transplanted melanoma (B16BL6-MICA) by activating and recruiting mouse NK and CD8+ T cells. The anti-melanoma effect of human dsNKG2D-IL-15 in C57BL/6 mice was mostly decreased by the in vivo depletion of mouse NK cells. These data highlight the potential use of human dsNKG2D-IL-15 for tumor therapy.Cellular & Molecular Immunology advance online publication, 14 September 2015; doi:10.1038/cmi.2015.81.

IL-15 receptor α signaling constrains the development of IL-17-producing γδ T cells

The development and homeostasis of γδ T cells is highly dependent on distinct cytokine networks. Here we examine the role of IL-15 and its unique receptor, IL-15Rα, in the development of IL-17-producing γδ (γδ-17) T cells. Phenotypic analysis has shown that CD44(high) γδ-17 cells express IL-15Rα and the common gamma chain (CD132), yet lack the IL-2/15Rβ chain (CD122). Surprisingly, we found an enlarged population of γδ-17 cells in the peripheral and mesenteric lymph nodes of adult IL-15Rα KO mice, but not of IL-15 KO mice. The generation of mixed chimeras from neonatal thymocytes indicated that cell-intrinsic IL-15Rα expression was required to limit IL-17 production by γδ T cells. γδ-17 cells also were increased in the peripheral lymph nodes of transgenic knock-in mice, where the IL-15Rα intracellular signaling domain was replaced with the intracellular portion of the IL-2Rα chain (that lacks signaling capacity). Finally, an analysis of neonatal thymi revealed that the CD44(lo/int) precursors of γδ-17 cells, which also expressed IL-15Rα, were increased in newborn mice deficient in IL-15Rα signaling, but not in IL-15 itself. Thus, these findings demonstrate that signaling through IL-15Rα regulates the development of γδ-17 cells early in ontogeny, with long-term effects on their peripheral homeostasis in the adult.

Reactive oxygen species in psoriasis and psoriasis arthritis: relevance to human disease

Psoriasis (Ps) is a chronic, immune-mediated, skin inflammatory disease affecting up to 3% of the population worldwide. Different environmental triggers initiate this complex multifactorial syndrome. Many individuals affected by Ps (6-26%) develop inflammatory disease in other organs, often in the joints as in psoriasis arthritis (PsA). Animal models that reflect the typical Ps syndrome, including both skin and joint pathology as in Ps and PsA, are valuable tools for dissecting disease pathways leading to clinical manifestations. In this context, we developed a new acute Ps and PsA-like disease model that appears after exposure to Saccharomyces cerevisiae mannan in certain mouse strains. The disease was found to be triggered by mannan-activated macrophages, leading to the activation of a pathogenic interleukin-17 pathway involving innate lymphocytes. Interestingly, the production of reactive oxygen species protected the mice from the triggering of this pathway and ameliorated Ps and PsA development.

An alternatively spliced IL-15 isoform modulates abrasion-induced keratinocyte activation

In a routine phenotype-driven screen, we identified a point mutation in exon 7 of the IL-15 gene in Pedigree 191 (deficient memory (DM)) of N-ethyl-N-nitrosourea mutagenized mice. The DM epidermis expressed an alternatively spliced IL-15 mRNA isoform, IL-15ΔE7, and a wild-type (WT) IL-15 isoform at comparable levels. Mechanical stimulation of DM skin or DM skin graft transplanted onto the WT host resulted in reduced keratinocyte activation and inhibition of neutrophil infiltration into the dermis, demonstrating that DM keratinocytes produced less inflammatory response to external stimulation. Ectopic expression of IL-15ΔE7 in WT skin prevented abrasion-induced epidermal thickening, blocked the accumulation of nuclear antigen Ki67(+) cells in the basal and the suprabasal cell layers, increased loricrin expression, and also increased keratinocyte CXCL1 and G-CSF production. IL-15ΔE7 also profoundly blocked neutrophil infiltration in SDS- or immiquimod (IMQ)-treated WT skin. Recombinant IL-15ΔE7 failed to activate STAT-5 and its downstream target bcl-2 expression. Our study points to IL-15ΔE7 as a potential therapeutic agent for treating neutrophilia-associated inflammatory skin disorders.

A GRHL3-regulated repair pathway suppresses immune-mediated epidermal hyperplasia

Dermal infiltration of T cells is an important step in the onset and progression of immune-mediated skin diseases such as psoriasis; however, it is not known whether epidermal factors play a primary role in the development of these diseases. Here, we determined that the prodifferentiation transcription factor grainyhead-like 3 (GRHL3), which is essential during epidermal development, is dispensable for adult skin homeostasis, but required for barrier repair after adult epidermal injury. Consistent with activation of a GRHL3-regulated repair pathway in psoriasis, we found that GRHL3 is upregulated in lesional skin and binds known epidermal differentiation gene targets. Using an imiquimod-induced model of immune-mediated epidermal hyperplasia, we found that mice lacking GRHL3 have an exacerbated epidermal damage response, greater sensitivity to disease induction, delayed resolution of epidermal lesions, and resistance to anti-IL-22 therapy compared with WT animals. ChIP-Seq and gene expression profiling of murine skin revealed that while GRHL3 regulates differentiation pathways both during development and during repair from immune-mediated damage, it targets distinct sets of genes in the 2 processes. In particular, GRHL3 suppressed a number of alarmin and other proinflammatory genes after immune injury. This study identifies a GRHL3-regulated epidermal barrier repair pathway that suppresses disease initiation and helps resolve existing lesions in immune-mediated epidermal hyperplasia.

Mechanisms regulating skin immunity and inflammation

Immune responses in the skin are important for host defence against pathogenic microorganisms. However, dysregulated immune reactions can cause chronic inflammatory skin diseases. Extensive crosstalk between the different cellular and microbial components of the skin regulates local immune responses to ensure efficient host defence, to maintain and restore homeostasis, and to prevent chronic disease. In this Review, we discuss recent findings that highlight the complex regulatory networks that control skin immunity, and we provide new paradigms for the mechanisms that regulate skin immune responses in host defence and in chronic inflammation.

Increasing the biological activity of IL-2 and IL-15 through complexing with anti-IL-2 mAbs and IL-15Rα-Fc chimera

IL-2 and IL-15 are structurally relative cytokines that share two receptor subunits, CD132 (γ(c) chain) and CD122 (β chain). However, the expression pattern and physiological role of IL-2 and IL-15 private receptor α chains CD25 and IL-15Rα, respectively, are strikingly different. CD25, together with CD122 and CD132, forms a trimeric high affinity IL-2 receptor that is expressed and functions on cells acquiring an IL-2 signal. Conversely, IL-15Rα is expressed and binds IL-15 with high affinity per se already in the endoplasmic reticulum of the IL-15 producing cells and it presents IL-15 to cells expressing CD122/CD132 dimeric receptor in trans. Thus, while IL-2 is secreted almost exclusively by activated T cells and acts as a free molecule, IL-15 is expressed mostly by myeloid cells and works as a cell surface-associated cytokine. Interestingly, the in vivo biological activity of IL-2 can be dramatically increased through complexing with certain anti-IL-2 mAbs; such IL-2/anti-IL-2 mAbs immunocomplexes selectively stimulate the proliferation of a distinct population of immune cells, depending on the clone of the anti-IL-2 mAb used. IL-2/S4B6 mAb immunocomplexes are highly stimulatory for CD122(high) populations (memory CD8(+) T and NK cells) and intermediately also for CD25(high) populations (Treg and activated T cells), while IL-2/JES6-1 mAb immunocomplexes enormously expand only CD25(high) cells. Although IL-2 immunocomplexes are much more potent than IL-2 in vivo, they show comparable to slightly lower activity in vitro. The in vivo biological activity of IL-15 can be dramatically increased through complexing with recombinant IL-15Rα-Fc chimera; however, IL-15/IL-15Rα-Fc complexes are significantly more potent than IL-15 both in vivo and in vitro. In this review we summarize and discuss the features and biological relevance of IL-2/anti-IL-2 mAbs and IL-15/IL-15Rα-Fc complexes, and try to foreshadow their potential in immunological research and immunotherapy.

The unconventional expression of IL-15 and its role in NK cell homeostasis

Natural killer (NK) cells are the founding members of the innate lymphoid cell family and contribute to the rapid production of inflammatory mediators upon pathogen detection. The evolution of receptors for self major histocompatibility complex-I and stress-induced ligands also bestows upon NK cells an important effector role in the clearance of virus-infected and transformed cells. NK cells are dependent on the pleiotropic cytokine interleukin (IL)-15 for their development, differentiation and optimal function. Here I review the regulation of IL-15 in vivo, its role in driving NK cell differentiation and discuss the function of NK cell diversification with regard to innate immunity.