Insulin-dependent diabetes induced by pancreatic beta cell expression of IL-15 and IL-15Rα

Loop Catalog: a comprehensive HiChIP database of human and mouse samples

HiChIP enables cost-effective and high-resolution profiling of chromatin loops. To leverage the increasing number of HiChIP datasets, we developed Loop Catalog (https://loopcatalog.lji.org), a web-based database featuring loop calls from 1000+ distinct human and mouse HiChIP samples from 152 studies plus 44 high-resolution Hi-C samples. We demonstrate its utility for interpreting GWAS and eQTL variants through SNP-to-gene linking, identifying enriched sequence motifs and motif pairs, and generating regulatory networks and 2D representations of chromatin structure. Our catalog spans over 4.19M unique loops, and with embedded analysis modules, constitutes an important resource for the field.

GM-CSF distinctly impacts human monocytes and macrophages via ERK1/2-dependent pathways

Human monocytes and macrophages are two major myeloid cell subsets with similar and distinct functions in tissue homeostasis and immune responses. GM-CSF plays a fundamental role in myeloid cell differentiation and activation. Hence, we compared the effects of GM-CSF on the expression of several immune mediators by human monocytes and monocyte-derived macrophages obtained from healthy donors. We report that GM-CSF similarly elevated the expression of CD80 and ICAM-1 and reduced HLA-DR levels on both myeloid cell subsets. However, GM-CSF increased the percentage of macrophages expressing surface IL-15 but reduced the proportion of monocytes carrying surface IL-15. Moreover, GM-CSF significantly increased the secretion of IL-4, IL-6, TNF, CXCL10, and IL-27 by macrophages while reducing the secretion of IL-4 and CXCL10 by monocytes. We show that GM-CSF triggered ERK1/2, STAT3, STAT5, and SAPK/JNK pathways in both myeloid subsets. Using a pharmacological inhibitor (U0126) preventing ERK phosphorylation, we demonstrated that this pathway was involved in both the GM-CSF-induced increase and decrease of the percentage of IL-15+ macrophages and monocytes, respectively. Moreover, ERK1/2 contributed to GM-CSF-triggered secretion of IL-4, IL-6, TNF, IL-27 and CXCL10 by macrophages. However, the ERK1/2 pathway exhibited different roles in monocytes and macrophages for the GM-CSF-mediated impact on surface makers (CD80, HLA-DR, and ICAM-1). Our data demonstrate that GM-CSF stimulation induces differential responses by human monocytes and monocyte-derived macrophages and that some but not all of these effects are ERK-dependent.

Granulocyte-macrophage colony-stimulating factor-stimulated human macrophages demonstrate enhanced functions contributing to T-cell activation

Granulocyte-macrophage colony-stimulating factor (GM-CSF) has been implicated in numerous chronic inflammatory diseases, including multiple sclerosis (MS). GM-CSF impacts multiple properties and functions of myeloid cells via species-specific mechanisms. Therefore, we assessed the effect of GM-CSF on different human myeloid cell populations found in MS lesions: monocyte-derived macrophages (MDMs) and microglia. We previously reported a greater number of interleukin (IL)-15⁺ myeloid cells in the brain of patients with MS than in controls. Therefore, we investigated whether GM-CSF exerts its deleterious effects in MS by increasing IL-15 expression on myeloid cells. We found that GM-CSF increased the proportion of IL-15⁺ cells and/or IL-15 levels on nonpolarized, M1-polarized and M2-polarized MDMs from healthy donors and patients with MS. GM-CSF also increased IL-15 levels on human adult microglia. When cocultured with GM-CSF-stimulated MDMs, activated autologous CD8⁺ T lymphocytes secreted and expressed significantly higher levels of effector molecules (e.g. interferon-γ and GM-CSF) compared with cocultures with unstimulated MDMs. However, neutralizing IL-15 did not attenuate enhanced effector molecule expression on CD8⁺ T lymphocytes triggered by GM-CSF-stimulated MDMs. We showed that GM-CSF stimulation of MDMs increased their expression of CD80 and ICAM-1 and their secretion of IL-6, IL-27 and tumor necrosis factor. These molecules could participate in boosting the effector properties of CD8⁺ T lymphocytes independently of IL-15. By contrast, GM-CSF did not alter CD80, IL-27, tumor necrosis factor and chemokine (C-X-C motif) ligand 10 expression/secretion by human microglia. Therefore, our results underline the distinct impact of GM-CSF on human myeloid cells abundantly present in MS lesions.

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.

The implications of IL-15 trans-presentation on the immune response

Interleukin-15 is a pleiotropic cytokine type I four alpha-helical bundle cytokine that along with IL-2, IL-4, IL-7, IL-9, and IL-21 shares the common cytokine receptor γ chain, γ_c. IL-15 is vital for the development, survival, and expansion of natural killer cells and for the development of CD8⁺ memory T cells. Whereas other family γ_c cytokines signal by directly binding to their target cells, IL-15 is distinctive in that it binds to IL-15Rα, a sushi domain containing binding protein that is expressed on a number of cell types, including monocytes and dendritic cells as well as T cells, and then is trans-presented to responding cells that express IL-2Rβ and γ_c. This distinctive mechanism for IL-15 relates to its role in signaling in the context of cell-cell interactions and signaling synapses. The actions of IL-15 and ways of manipulating its actions to potential therapeutic benefit are discussed.

Possible association of rotavirus IgG with cytokine expression levels and dyslipidemia in rotavirus-infected type 1 diabetic children

Background

Rotavirus (RV) has been postulated as a viral trigger for the onset of autoimmune disorders, such as type 1 diabetes (T1D). This study aimed to examine the conceivable association of RV IgG with cytokine levels and dyslipidemia in the pathogenesis of pediatric T1D.

Methods

This study included 30 healthy controls and 80 children with T1D who were divided into two groups based on the time since their T1D diagnosis: newly diagnosed (ND ≤ 1 year; n = 30) and previously diagnosed (PD > 1 year; n = 50). ND and PD patients were also separated into negative and positive according to IgG detection (RV IgG⁻, ND⁻, and PD⁻; RV IgG⁺, ND⁺, and PD⁺).

Results

Positive polymerase chain reaction for RVs was evidenced in 7.5% of children with T1D. Anti-RV IgG was 30% and 36% in ND and PD, respectively, compared to healthy controls (2 of 30, 6.6%; P < 0.05). Fasting blood sugar and hemoglobin A1c significantly increased in PD⁺ compared to PD⁻. Interferon-γ and interleukin (IL)-15 levels significantly increased. IL-12 and IL-22 mRNA expression was upregulated in ND⁺ patients compared to that in ND⁻ patients. IL-37 mRNA expression was significantly downregulated in ND⁻ and ND⁺ patients compared to that in healthy controls. Total cholesterol and high- and low-density lipoprotein-cholesterol levels were significantly lower in PD⁺ than in PD⁻; whereas triglyceride levels were higher than those in healthy controls.

Conclusions

This study suggested that anti-RV IgG may have a role in the pathogenesis, development, and progression of T1D, and RV infections are implicated in dyslipidemia and inflammation status.

Supplementary information

The online version contains supplementary material available at 10.1007/s11033-022-07573-0.

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.

The Influence of Different Types of Diabetes on Vascular Complications

The final outcome of diabetes is chronic complications, of which vascular complications are the most serious, which is the main cause of death for diabetic patients and the direct cause of the increase in the cost of diabetes. Type 1 and type 2 diabetes are the main types of diabetes, and their pathogenesis is completely different. Type 1 diabetes is caused by genetics and immunity to destroy a large number of β cells, and insulin secretion is absolutely insufficient, which is more prone to microvascular complications. Type 2 diabetes is dominated by insulin resistance, leading to atherosclerosis, which is more likely to progress to macrovascular complications. This article explores the pathogenesis of two types of diabetes, analyzes the pathogenesis of different vascular complications, and tries to explain the different trends in the progression of different types of diabetes to vascular complications, in order to better prevent diabetes and its vascular complications.

Endogenous Levels of Gamma Amino-Butyric Acid Are Correlated to Glutamic-Acid Decarboxylase Antibody Levels in Type 1 Diabetes

Gamma-aminobutyric acid (GABA) is an important inhibitory neurotransmitter in the central nervous system (CNS) and outside of the CNS, found in the highest concentrations in immune cells and pancreatic beta-cells. GABA is gaining increasing interest in diabetes research due to its immune-modulatory and beta-cell stimulatory effects and is a highly interesting drug candidate for the treatment of type 1 diabetes (T1D). GABA is synthesized from glutamate by glutamic acid decarboxylase (GAD), one of the targets for autoantibodies linked to T1D. Using mass spectrometry, we have quantified the endogenous circulating levels of GABA in patients with new-onset and long-standing T1D and found that the levels are unaltered when compared to healthy controls, i.e., T1D patients do not have a deficit of systemic GABA levels. In T1D, GABA levels were negatively correlated with IL-1 beta, IL-12, and IL-15 15 and positively correlated to levels of IL-36 beta and IL-37. Interestingly, GABA levels were also correlated to the levels of GAD-autoantibodies. The unaltered levels of GABA in T1D patients suggest that the GABA secretion from beta-cells only has a minor impact on the circulating systemic levels. However, the local levels of GABA could be altered within pancreatic islets in the presence of GAD-autoantibodies.

The Transcriptome and Epigenome Reveal Novel Changes in Transcription Regulation During Pancreatic Rat Islet Maturation

Islet function is critical for normal glucose homeostasis. Unlike adult β cells, fetal and neonatal islets are more proliferative and have decreased insulin secretion in response to stimuli. However, the underlying mechanisms governing functional maturity of islets have not been completely elucidated. Pancreatic islets comprise different cell types. The microenvironment of islets and interactions between these cell types are critical for β-cell development and maturation. Thus, the study of intact islets is optimal to identify novel molecular mechanisms controlling islet functional development. Transcriptomes and genome-wide histone landscapes of H3K4me3, H3K27me3, and H3K27Ac from intact islets isolated from 2- and 10-week-old Sprague-Dawley rats were integrated to elucidate genes and pathways modulating islet development, as well as the contribution of epigenetic regulation. A total of 4489 differentially expressed genes were identified; 2289 and 2200 of them were up- and down-regulated in 10-week islets, respectively. Ingenuity Pathway Analysis revealed critical pathways regulating functional maturation of islets, including nutrient sensing, neuronal function, immune function, cell replication, and extracellular matrix. Furthermore, we identified significant changes in enrichment of H3K4me3, H3K27me3, and H3K27Ac marks, which correlated with expression changes of genes critical for islet function. These histone marks were enriched at critical transcription factor-binding motifs, such as Hoxa9, C/EBP-β, Gata1, Foxo1, E2f1, E2f3, and Mafb. In addition, our chromatin immunoprecipitation sequencing data revealed multiple potential bivalent genes whose poised states changed with maturation. Collectively, our current study identified critical novel pathways for mature islet function and suggested a role for histone modifications in regulating islet development and maturation.

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.

Divergent genes in gerbils: prevalence, relation to GC-biased substitution, and phenotypic relevance

Background

Two gerbil species, sand rat (Psammomys obesus) and Mongolian jird (Meriones unguiculatus), can become obese and show signs of metabolic dysregulation when maintained on standard laboratory diets. The genetic basis of this phenotype is unknown. Recently, genome sequencing has uncovered very unusual regions of high guanine and cytosine (GC) content scattered across the sand rat genome, most likely generated by extreme and localized biased gene conversion. A key pancreatic transcription factor PDX1 is encoded by a gene in the most extreme GC-rich region, is remarkably divergent and exhibits altered biochemical properties. Here, we ask if gerbils have proteins in addition to PDX1 that are aberrantly divergent in amino acid sequence, whether they have also become divergent due to GC-biased nucleotide changes, and whether these proteins could plausibly be connected to metabolic dysfunction exhibited by gerbils.

Results

We analyzed ~ 10,000 proteins with 1-to-1 orthologues in human and rodents and identified 50 proteins that accumulated unusually high levels of amino acid change in the sand rat and 41 in Mongolian jird. We show that more than half of the aberrantly divergent proteins are associated with GC biased nucleotide change and many are in previously defined high GC regions. We highlight four aberrantly divergent gerbil proteins, PDX1, INSR, MEDAG and SPP1, that may plausibly be associated with dietary metabolism.

Conclusions

We show that through the course of gerbil evolution, many aberrantly divergent proteins have accumulated in the gerbil lineage, and GC-biased nucleotide substitution rather than positive selection is the likely cause of extreme divergence in more than half of these. Some proteins carry putatively deleterious changes that could be associated with metabolic and physiological phenotypes observed in some gerbil species. We propose that these animals provide a useful model to study the ‘tug-of-war’ between natural selection and the excessive accumulation of deleterious substitutions mutations through biased gene conversion.

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.

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.

Cytokines in type 1 diabetes: mechanisms of action and immunotherapeutic targets

Cytokines play crucial roles in orchestrating complex multicellular interactions between pancreatic β cells and immune cells in the development of type 1 diabetes (T1D) and are thus potential immunotherapeutic targets for this disorder. Cytokines that can induce regulatory functions-for example, IL-10, TGF-β and IL-33-are thought to restore immune tolerance and prevent β-cell damage. By contrast, cytokines such as IL-6, IL-17, IL-21 and TNF, which promote the differentiation and function of diabetogenic immune cells, are thought to lead to T1D onset and progression. However, targeting these dysregulated cytokine networks does not always result in consistent effects because anti-inflammatory or proinflammatory functions of cytokines, responsible for β-cell destruction, are context dependent. In this review, we summarise the current knowledge on the involvement of well-known cytokines in both the initiation and destruction phases of T1D and discuss advances in recently discovered roles of cytokines. Additionally, we emphasise the complexity and implications of cytokine modulation therapy and discuss the ways in which this strategy has been translated into clinical trials.

The benefits of physical exercise for the health of the pancreatic β-cell: a review of the evidence

NEW FINDINGS

What is the topic of this review? This review discusses the evidence of the benefits of exercise training for β-cell health through improvements in function, proliferation and survival which may have implications in the treatment of diabetes. What advances does it highlight? This review highlights how exercise may modulate β-cell health in the context of diabetes and highlights the need for further exploration of whether β-cell preserving effects of exercise translates to T1D.

ABSTRACT

Physical exercise is a core therapy for type 1 and type 2 diabetes. Whilst the benefits of exercise for different physiological systems are recognised, the effect of exercise specifically on the pancreatic β-cell is not well described. Here we review the effects of physical exercise on β-cell health. We show that exercise improves β-cell mass and function. The improved function manifests primarily through the increased insulin content of the β-cell and its increased ability to secrete insulin in response to a glucose stimulus. We review the evidence relating to glucose sensing, insulin signalling, β-cell proliferation and β-cell apoptosis in humans and animal models with acute exercise and following exercise training programmes. Some of the mechanisms through which these benefits manifest are discussed.

Identification of a γc Receptor Antagonist That Prevents Reprogramming of Human Tissue-resident Cytotoxic T Cells by IL15 and IL21

BACKGROUND & AIMS

Gamma chain (γc) cytokines (interleukin [IL]2, IL4, IL7, IL9, IL15, and IL21) signal via a common γc receptor. IL2 regulates the immune response, whereas IL21 and IL15 contribute to development of autoimmune disorders, including celiac disease. We investigated whether BNZ-2, a peptide designed to inhibit IL15 and IL21, blocks these cytokines selectively and its effects on intraepithelial cytotoxic T cells.

METHODS

We obtained duodenal biopsies from 9 patients with potential celiac disease (positive results from tests for anti-TG2 but no villous atrophy), 30 patients with untreated celiac disease (with villous atrophy), and 5 patients with treated celiac disease (on a gluten-free diet), as well as 43 individuals without celiac disease (controls). We stimulated primary intestinal intraepithelial CD8⁺ T-cell lines, or CD8⁺ T cells directly isolated from intestinal biopsies, with γc cytokines in presence or absence of BNZ-2. Cells were analyzed by immunoblots, flow cytometry, or RNA-sequencing analysis for phosphorylation of signaling molecules, gene expression profiles, proliferation, and levels of granzyme B.

RESULTS

Duodenal tissues from patients with untreated celiac disease had increased levels of messenger RNAs encoding IL15 receptor subunit alpha (IL15RA) and IL21 compared with tissues from patients with potential celiac disease and controls. Activation of intraepithelial cytotoxic T cells with IL15 or IL21 induced separate signaling pathways; incubation of the cells with IL15 and IL21 cooperatively increased their transcriptional activity, proliferation, and cytolytic properties. BNZ-2 specifically inhibited the effects of IL15 and IL21, but not of other γc cytokines.

CONCLUSIONS

We found increased expression of IL15RA and IL21 in duodenal tissues from patients with untreated celiac disease compared with controls. IL15 and IL21 cooperatively activated intestinal intraepithelial cytotoxic T cells. In particular, they increased their transcriptional activity, proliferation, and cytolytic activity. The peptide BNZ-2 blocked these effects, but not those of other γc cytokines, including IL2. BNZ-2 might be used to prevent cytotoxic T-cell-mediated tissue damage in complex immune disorders exhibiting upregulation of IL15 and IL21.

Interleukin-27 Is Essential for Type 1 Diabetes Development and Sjögren Syndrome-like Inflammation

Human genetic studies implicate interleukin-27 (IL-27) in the pathogenesis of type 1 diabetes (T1D), but the underlying mechanisms remain largely unexplored. To further define the role of IL-27 in T1D, we generated non-obese diabetic (NOD) mice deficient in IL-27 or IL-27Rα. In contrast to wild-type NOD mice, both NOD.Il27-/- and NOD.Il27ra-/- strains are completely resistant to T1D. IL-27 from myeloid cells and IL-27 signaling in T cells are critical for T1D development. IL-27 directly alters the balance of regulatory T cells (Tregs) and T helper 1 (Th1) cells in pancreatic islets, which in turn modulates the diabetogenic activity of CD8 T cells. IL-27 also directly enhances the effector function of CD8 T cells within pancreatic islets. In addition to T1D, IL-27 signaling in T cells is also required for lacrimal and salivary gland inflammation in NOD mice. Our study reveals that IL-27 contributes to autoimmunity in NOD mice through multiple mechanisms and provides substantial evidence to support its pathogenic role in human T1D.

Oxidative stress-induced IL-15 trans-presentation in keratinocytes contributes to CD8+ T cells activation via JAK-STAT pathway in vitiligo

Oxidative stress and effector memory CD8⁺ T cells have been greatly implicated in vitiligo pathogenesis. However, the crosstalk between these two crucial pathogenic factors has been merely investigated. IL-15 has been regarded as an important cytokine exerting its facilitative effect on memory CD8⁺ T cells function in various autoimmune diseases. In the present study, we initially discovered that the IL-15 expression was significantly increased in vitiligo epidermis and highly associated with epidermal H₂O₂ content. In addition, epidermal IL-15 expression was mainly derived from keratinocytes. Then, we showed that oxidative stress promoted IL-15 and IL-15Rα expression as well as IL-15 trans-presentation by activating NF-κB signaling in keratinocytes. What's more, the trans-presented IL-15, rather than the secreted one, was accounted for the potentiation of CD8⁺ T_EMs activation. We further investigated the mechanism underlying trans-presented IL-15 in potentiating CD8⁺ T_EMs activation and found that the blockage of IL-15-JAK-STAT signaling could be a potent therapeutic approach. Taken together, our results demonstrate that oxidative stress-induced IL-15 trans-presentation in keratinocytes contributes to the activation of CD8⁺ T_EMs, providing a novel mechanism by which oxidative stress initiates autoimmunity in vitiligo.

Regulation of Diabetogenic Immunity by IL-15-Activated Regulatory CD8 T Cells in Type 1 Diabetes

Unchecked collaboration between islet-reactive T and B lymphocytes drives type 1 diabetes (T1D). In the healthy setting, CD8 T regulatory cells (Tregs) terminate ongoing T-B interactions. We determined that specific CD8 Tregs from NOD mice lack suppressive function, representing a previously unreported regulatory cell deficit in this T1D-prone strain. NOD mice possess 11-fold fewer Ly-49+ CD8 Tregs than nonautoimmune mice, a deficiency that worsens as NOD mice age toward diabetes and leaves them unable to regulate CD4 T follicular helper cells. As IL-15 is required for Ly-49+ CD8 Treg development, we determined that NOD macrophages inadequately trans-present IL-15. Despite reduced IL-15 trans-presentation, NOD Ly-49+ CD8 Tregs can effectively transduce IL-15-mediated survival signals when they are provided. Following stimulation with an IL-15/IL-15Ra superagonist complex, Ly-49+ CD8 Tregs expanded robustly and became activated to suppress the Ag-specific Ab response. IL-15/IL-15Ra superagonist complex-activated CD8+CD122+ T cells also delayed diabetes transfer, indicating the presence of an underactivated CD8 T cell subset with regulatory capacity against late stage T1D. We identify a new cellular contribution to anti-islet autoimmunity and demonstrate the correction of this regulatory cell deficit. Infusion of IL-15-activated CD8 Tregs may serve as an innovative cellular therapy for the treatment of T1D.

Interleukin-27 promotes CD8+ T cell reconstitution following antibody-mediated lymphoablation

Antibody-mediated lymphoablation is used in solid organ and stem cell transplantation and autoimmunity. Using murine anti-thymocyte globulin (mATG) in a mouse model of heart transplantation, we previously reported that the homeostatic recovery of CD8+ T cells requires help from depletion-resistant memory CD4+ T cells delivered through CD40-expressing B cells. This study investigated the mechanisms by which B cells mediate CD8+ T cell proliferation in lymphopenic hosts. While CD8+ T cell recovery required MHC class I expression in the host, the reconstitution occurred independently of MHC class I, MHC class II, or CD80/CD86 expression on B cells. mATG lymphoablation upregulated the B cell expression of several cytokine genes, including IL-15 and IL-27, in a CD4-dependent manner. Neither treatment with anti-CD122 mAb nor the use of IL-15Rα-/- recipients altered CD8+ T cell recovery after mATG treatment, indicating that IL-15 may be dispensable for T cell proliferation in our model. Instead, IL-27 neutralization or the use of IL-27Rα-/- CD8+ T cells inhibited CD8+ T cell proliferation and altered the phenotype and cytokine profile of reconstituted CD8+ T cells. Our findings uncover what we believe is a novel role of IL-27 in lymphopenia-induced CD8+ T cell proliferation and suggest that targeting B cell-derived cytokines may increase the efficacy of lymphoablation and improve transplant outcomes.

Enterovirus infection and type 1 diabetes: unraveling the crime scene

Enteroviruses (EV) have been historically associated to type 1 diabetes. Definitive proof for their implication in disease development is lacking, but growing evidence suggests that they could be involved in beta cell destruction either directly by killing beta cells or indirectly by creating an exacerbated inflammatory response in the islets, capable of attracting autoreactive T cells to the 'scene of the crime'. Epidemiological and serological studies have been associated with the appearance of islet autoimmunity and EV RNA has been detected in prospective studies. In addition, the EV capsid protein has been detected in the islets of recent-onset type 1 diabetic donors, suggesting the existence of a low-grade EV infection that could become persistent. Increasing evidence in the field shows that a 'viral signature' exists in type 1 diabetes and involves interferon responses that could be sustained during prolonged periods. These include the up-regulation of markers such as protein kinase R (PKR), melanoma differentiation-associated protein 5 (MDA5), retinoic acid inducible gene I (RIG-I), myxovirus resistance protein (MxA) and human leukocyte antigen-I (HLA-I) and the release of chemokines able to attract immune cells to the islets leading to insulitis. In this scenario, the hyperexpression of HLA-I molecules would promote antigen presentation to autoreactive T cells, favoring beta cell recognition and, ultimately, destruction. In this review, an overview is provided of the standing evidence that implicates EVs in beta cell 'murder', the time-line of events is investigated from EV entry in the cell to beta cell death and possible accomplices are highlighted that might be involved in beta cell demise.

The diabetes pandemic and associated infections: suggestions for clinical microbiology

There are 425 million people with diabetes mellitus in the world. By 2045, this figure will grow to over 600 million. Diabetes mellitus is classified among noncommunicable diseases. Evidence points to a key role of microbes in diabetes mellitus, both as infectious agents associated with the diabetic status and as possible causative factors of diabetes mellitus. This review takes into account the different forms of diabetes mellitus, the genetic determinants that predispose to type 1 and type 2 diabetes mellitus (especially those with possible immunologic impact), the immune dysfunctions that have been documented in diabetes mellitus. Common infections occurring more frequently in diabetic vs. nondiabetic individuals are reviewed. Infectious agents that are suspected of playing an etiologic/triggering role in diabetes mellitus are presented, with emphasis on enteroviruses, the hygiene hypothesis, and the environment. Among biological agents possibly linked to diabetes mellitus, the gut microbiome, hepatitis C virus, and prion-like protein aggregates are discussed. Finally, preventive vaccines recommended in the management of diabetic patients are considered, including the bacillus calmette-Guerin vaccine that is being tested for type 1 diabetes mellitus. Evidence supports the notion that attenuation of immune defenses (both congenital and secondary to metabolic disturbances as well as to microangiopathy and neuropathy) makes diabetic people more prone to certain infections. Attentive microbiologic monitoring of diabetic patients is thus recommendable. As genetic predisposition cannot be changed, research needs to identify the biological agents that may have an etiologic role in diabetes mellitus, and to envisage curative and preventive ways to limit the diabetes pandemic.

CD122 signaling in CD8+ memory T cells drives costimulation-independent rejection

Interrupting T cell costimulatory signals as a strategy to control undesired immune responses, such as occur in autoimmunity or transplantation, has the potential to alleviate many of the unwanted side effects associated with current immunosuppressive therapies. Belatacept, a high-affinity version of CTLA4-Ig that blocks ligand ligation to CD28, has been approved for use in kidney transplant recipients. Despite the long-term benefits associated with its use, such as improved renal function and lower cardiovascular risk, a subset of patients treated with belatacept experience elevated rates of acute T cell-mediated rejection, tempering enthusiasm for its use. Here we demonstrate that costimulation-independent T cell alloreactivity relies on signaling through CD122, the shared IL-2 and IL-15 receptor β-chain. Combined costimulatory and CD122 blockade improved survival of transplanted tissue in mice and nonhuman primates by controlling proliferation and effector function of CD8+ T cells. The high-affinity IL-2 receptor was dispensable for memory CD8+ T cell responses, whereas signaling through CD122 as a component of the high-affinity IL-15 receptor was critical for costimulation-independent memory CD8+ T cell recall, distinguishing specific roles for IL-2 and IL-15 in T cell activation. These studies outline a novel approach for clinical optimization of costimulatory blockade strategies in transplantation by targeting CD122.

Human intraepithelial lymphocytes

The location of intraepithelial lymphocytes (IEL) between epithelial cells, their effector memory, cytolytic and inflammatory phenotype positions them to kill infected epithelial cells and protect the intestine against pathogens. Human TCRαβ+CD8αβ+ IEL have the dual capacity to recognize modified self via natural killer (NK) receptors (autoreactivity) as well as foreign antigen via the T cell receptor (TCR), which is accomplished in mouse by two cell subsets, the naturally occurring TCRαβ+CD8αα+ and adaptively induced TCRαβ+CD8αβ+ IEL subsets, respectively. The private/oligoclonal nature of the TCR repertoire of both human and mouse IEL suggests local environmental factors dictate the specificity of IEL responses. The line between sensing of foreign antigens and autoreactivity is blurred for IEL in celiac disease, where recognition of stress ligands by induced activating NK receptors in conjunction with inflammatory signals such as IL-15 can result in low-affinity TCR/non-cognate antigen and NK receptor/stress ligand interactions triggering destruction of intestinal epithelial cells.

Optimal α-lipoic acid strengthen immunity of young grass carp (Ctenopharyngodon idella) by enhancing immune function of head kidney, spleen and skin

This study was for the first time to investigate the effects of α-lipoic acid (LA) on growth and immune function of head kidney, spleen and skin in young grass carp (Ctenopharyngodon idella). A total of 540 healthy grass carp (with initial body weight at 216.59 ± 0.33 g) were randomly divided into six groups and fed six separate diets with graded dietary levels of LA for 70 days. Un-supplemented group did not find LA and its concentrations in the other five diets were 203.25, 403.82, 591.42, 781.25 and 953.18 mg kg^-1, respectively. After the growth trial, fish were challenged with A. hydrophila for 14 days. The results showed that, compared with the un-supplemented group, optimal LA improved lysozyme (LZ) and acid phosphatase (ACP) activities, enhanced complement 3 (C3), C4 and immunoglobulin (Ig) M contents and up-regulated hepcidin, liver expressed antimicrobial peptide (LEAP)-2A, LEAP-2B and β-defensin-1 mRNA levels in the head kidney, spleen and skin of young grass carp; meanwhile, optimal LA up-regulated anti-inflammatory cytokines transforming growth factor (TGF)-β1, TGF-β2, interleukin (IL)-4/13A (not IL-4/13B), IL-10 and IL-11 mRNA levels partly related to target of rapamycin (TOR) signaling and down-regulated pro-inflammatory cytokines tumor necrosis factor (TNF)-α, interferon (IFN)-γ2, IL-1β, IL-6, IL-8, IL-12p40 (not IL-12p35), IL-15 (not in the skin) and IL-17D mRNA levels partially associated with nuclear factor-kappa B (NF-κB) signaling in the head kidney, spleen and skin of young grass carp. Above results indicated that optimal LA enhanced the immune function of head kidney, spleen and skin in fish. Interestingly, excessive LA decreased the growth and impaired the immune function of head kidney, spleen and skin in fish. Finally, on the basis of the percent weight gain (PWG), the ability against skin hemorrhage and lesion, the IgM content in the head kidney and the LZ activity in the spleen, the optimal dietary LA levels were estimated to be 315.37, 382.33, 353.19 and 318.26 mg kg^-1 diet, respectively.

Selenium deficiency impaired immune function of the immune organs in young grass carp (Ctenopharyngodon idella)

This study aimed to investigate the effects of dietary selenium on resistance to skin haemorrhages and lesions and on immune function as well as the underlying mechanisms of those effects in the head kidney, spleen and skin of young grass carp (Ctenopharyngodon idella). A total of 540 healthy grass carp with initial body weight (226.48 ± 0.68 g) were randomly divided into six groups and fed six separate diets with graded dietary levels of selenium (0.025, 0.216, 0.387, 0.579, 0.795 and 1.049 mg/kg diet) for 80 days. After the feeding period, an immunization trial was performed by infection with Aeromonas hydrophila for 14 days. The results showed that, compared with the optimal selenium level, (1) selenium deficiency impaired the production of antibacterial compounds and immunoglobulins and down-regulated the transcript abundances of antimicrobial peptides and selenoproteins; (2) selenium deficiency aggravated inflammatory responses in part by up-regulating pro-inflammatory cytokines and down-regulating anti-inflammatory cytokines mRNA levels, which were partially related to [IKKα, β, γ/IκBα/NF-κB] signalling and [TOR/(S6K1, 4E-BP1)] signalling, respectively. Interestingly, selenium deficiency had no effect on the expression of TGF-β2, IL-4/13B, IL-10, IL-12p35, IL-15 (skin only) or 4E-BP2 in the head kidney, spleen and skin of young grass carp. Finally, based on the percent weight gain (PWG), the morbidity of skin haemorrhages and lesions, the ACP activity in the head kidney and the lysozyme activity in spleen, the optimal dietary selenium requirements for young grass carp were estimated to be 0.546-0.604 mg/kg diet. In summary, selenium deficiency decreased the growth performance and impaired the immune function in the head kidney, spleen and skin of young grass carp.

CD122 blockade restores immunological tolerance in autoimmune type 1 diabetes via multiple mechanisms

Signaling through IL-2/IL-15Rβ (CD122) is essential for the differentiation and function of T cells and NK cells. A mAb against CD122 has been implicated to suppress autoimmune type 1 diabetes (T1D) development in animal models. However, the mechanisms remain poorly understood. We find that in vivo administration of an anti-CD122 mAb (CD122 blockade) restores immune tolerance in nonobese diabetic (NOD) mice via multiple mechanisms. First, CD122 blockade selectively ablates pathogenic NK cells and memory phenotype CD8+ T cells from pancreatic islets. In contrast, islet CD4+Foxp3+ Tregs are only mildly affected. Second, CD122 blockade suppresses IFN-γ production in islet immune cells. Third, CD122 blockade inhibits the conversion of islet Th17 cells into diabetogenic Th1 cells. Furthermore, a combination of anti-CD122 mAb and Treg-trophic cytokines (IL-2 or IL-33) enhances the abundance and function of islet Tregs. In summary, these data provide crucial mechanistic insights into CD122 blockade-mediated immunoregulation and support therapeutic benefits of this combinational treatment in T1D.

Laser Microdissection Workflow for Isolating Nucleic Acids from Fixed and Frozen Tissue Samples

Laser Capture Microdissection has earned a permanent place among modern techniques connecting histology and molecular biology. Laser Capture Microdissection has become an invaluable tool in medical research as a means for collection of specific cell populations isolated from their environment. Such genomic sample enrichment dramatically increases the sensitivity and precision of downstream molecular assays used for biomarker discovery, monitoring disease onset and progression, and in the development of personalized medicine. The diversity of research targets (cancerous and precancerous lesions in clinical and animal research, cell pellets, rodent embryos, frozen tissues, archival repository slides, etc.) and scientific objectives present a challenge in establishing standard protocols for Laser Capture Microdissection. In the present chapter, we share our experiences in design and successful execution of numerous diverse microdissection projects, and provide considerations to be taken into account in planning a microdissection study. Our workflow and protocols are standardized for a wide range of animal and human tissues and adapted to downstream analysis platforms.

Increased Interleukin-35 Levels in Patients With Type 1 Diabetes With Remaining C-Peptide

OBJECTIVE

Many patients with long-standing type 1 diabetes have remaining functional β-cells. This study investigated immunological differences between patients with or without measurable remaining endogenous insulin production after ≥10 years duration of disease.

RESEARCH DESIGN AND METHODS

Patients (n = 113; ≥18 years of age) with type 1 diabetes and with disease duration of ≥10 years were recruited at Uppsala University Hospital. Residual β-cell function was determined with an ultrasensitive C-peptide ELISA. Circulating cytokines, including interleukin-35 (IL-35), were determined in plasma. Additional blood samples were collected from 14 of the identified C-peptide-positive patients and 12 of the C-peptide-negative patients, as well as from 15 healthy control subjects, and were used for immediate investigation of peripheral blood mononuclear cells.

RESULTS

The blood concentration of the cytokine IL-35 was markedly lower in C-peptide-negative patients, and this was associated with a simultaneous decrease in the proportion of IL-35⁺ regulatory T cells (Tregs), IL-35⁺ regulatory B cells, and IL-35-producing CD8⁺Foxp3⁺ cells. IL-35 has previously been shown to maintain the phenotype of Tregs, block the differentiation of T-helper 17 cells, and thereby dampen immune assaults to β-cells. We found that the proportions of IL-17a⁺ cells among the Tregs, CD4⁺ T cells, and CD8⁺ T cells were lower in the C-peptide-positive patients.

CONCLUSIONS

Patients with remaining endogenous β-cell function after >10 years duration of type 1 diabetes differ immunologically from other patients with long-standing type 1 diabetes. In particular, they have a much higher IL-35 production.

The decreased growth performance and impaired immune function and structural integrity by dietary iron deficiency or excess are associated with TOR, NF-κB, p38MAPK, Nrf2 and MLCK signaling in head kidney, spleen and skin of grass carp (Ctenopharyngodon idella)

This study was conducted to investigate the effects of dietary iron on the growth, and immune function and structural integrity in head kidney, spleen and skin as well as the underlying signaling of young grass carp (Ctenopharyngodon idella). Total 630 grass carp (242.32 ± 0.58 g) were fed diets containing graded levels of iron at 12.15 (basal diet), 35.38, 63.47, 86.43, 111.09, 136.37 mg/kg (diets 2-6 were added with ferrous fumarate) and 73.50 mg/kg (diet 7 was added with ferrous sulfate) diet for 60 days. Then, a challenge test was conducted by infection of Aeromonas hydrophila for 14 days. The results firstly showed that compared with optimal iron level, iron deficiency decreased lysozyme (LZ) and acid phosphatase (ACP) activities, complement 3 (C3), C4 and immunoglobulin M (IgM) contents and down-regulated the mRNA levels of antibacterial peptides, anti-inflammatory cytokines, inhibitor of κBα (IκBα), target of rapamycin (TOR) and ribosomal protein S6 kinase 1 (S6K1), whereas up-regulated the mRNA levels of pro-inflammatory cytokines, nuclear factor kappa B (NF-κB) p65, IκB kinases β (IKKβ) and eIF4E-binding protein (4E-BP) in head kidney and spleen of young grass carp (P < 0.05), indicating that iron deficiency impaired immune function in head kidney and spleen of fish. Secondly, iron deficiency down-regulated the mRNA levels of B-cell lymphoma-2 (Bcl-2), myeloid cell leukemia 1 (Mcl-1), and inhibitor of apoptosis protein (IAP), and decreased activities and mRNA levels of antioxidant enzymes, down-regulated the mRNA levels of NF-E2-related factor 2 (Nrf2) and tight junction complexes, and up-regulated mRNA levels of cysteinyl aspartic acid-protease (caspase) -2, -3, -7, -8, -9, apoptotic protease activating factor-1 (Apaf-1), Bcl-2 associated X protein (Bax), Fas ligand (FasL), p38 mitogen-activated protein kinase (p38MAPK), Kelch-like ECH-associating protein (Keap) 1a, Keap1b, claudin-12 and myosin light chain kinase (MLCK), and increased malondialdehyde (MDA), protein carbonyl (PC) and reactive oxygen species (ROS) contents in head kidney and spleen of young grass carp (P < 0.05), indicating that iron deficiency impaired structural integrity in head kidney and spleen of fish. Thirdly, iron deficiency increased skin hemorrhage and lesion morbidity, and impaired immune function and structural integrity in skin of fish. Fourthly, iron excess decreased growth and impaired the immune function and structural integrity in head kidney, spleen and skin of fish. Besides, in young grass carp, based on PWG and ability against skin hemorrhage and lesion, the efficacy of ferrous fumarate relative to ferrous sulfate was 140.32% and 126.48%, respectively, and the iron requirements based on PWG, ability against skin hemorrhage and lesion, ACP activities and MDA contents in head kidney and spleen were estimated to be 75.65, 87.03, 79.74, 78.93, 83.17 and 82.14 mg/kg diet (based on ferrous fumarate), respectively.

Clinical Recommendations for the Use of Islet Cell Autoantibodies to Distinguish Autoimmune and Non-Autoimmune Gestational Diabetes

Gestational diabetes mellitus (GDM) is defined as carbohydrate intolerance that begins or is first recognized during pregnancy. The prevalence of GDM is highly variable, depending on the population studied, and reflects the underlying pattern of diabetes in the population. GDM manifests by the second half of pregnancy and disappears following delivery in most cases, but is associated with the risk of subsequent diabetes development. Normal pregnancy induces carbohydrate intolerance to favor the availability of nutrients for the fetus, which is compensated by increased insulin secretion from the maternal pancreas. Pregnancy shares similarities with adiposity in metabolism to save energy, and both conditions favor the development of insulin resistance (IR) and low-grade inflammation. A highly complicated network of modified regulatory mechanisms may primarily affect carbohydrate metabolism by promoting autoimmune reactions to pancreatic β cells and affecting insulin function. As a result, diabetes development during pregnancy is facilitated. Depending on a pregnant woman's genetic susceptibility to diabetes, autoimmune mechanisms or IR are fundamental to the development autoimmune or non-autoimmune GDM, respectively. Pregnancy may facilitate the identification of women at risk of developing diabetes later in life; autoimmune and non-autoimmune GDM may be early markers of the risk of future type 1 and type 2 diabetes, respectively. The most convenient and efficient way to discriminate GDM types is to assess pancreatic β-cell autoantibodies along with diagnosing diabetes in pregnancy.

Interleukin-15 promotes intestinal dysbiosis with butyrate deficiency associated with increased susceptibility to colitis

Dysbiosis resulting in gut-microbiome alterations with reduced butyrate production are thought to disrupt intestinal immune homeostasis and promote complex immune disorders. However, whether and how dysbiosis develops before the onset of overt pathology remains poorly defined. Interleukin-15 (IL-15) is upregulated in distressed tissue and its overexpression is thought to predispose susceptible individuals to and have a role in the pathogenesis of celiac disease and inflammatory bowel disease (IBD). Although the immunological roles of IL-15 have been largely studied, its potential impact on the microbiota remains unexplored. Analysis of 16S ribosomal RNA-based inventories of bacterial communities in mice overexpressing IL-15 in the intestinal epithelium (villin-IL-15 transgenic (v-IL-15tg) mice) shows distinct changes in the composition of the intestinal bacteria. Although some alterations are specific to individual intestinal compartments, others are found across the ileum, cecum and feces. In particular, IL-15 overexpression restructures the composition of the microbiota with a decrease in butyrate-producing bacteria that is associated with a reduction in luminal butyrate levels across all intestinal compartments. Fecal microbiota transplant experiments of wild-type and v-IL-15tg microbiota into germ-free mice further indicate that diminishing butyrate concentration observed in the intestinal lumen of v-IL-15tg mice is the result of intrinsic alterations in the microbiota induced by IL-15. This reconfiguration of the microbiota is associated with increased susceptibility to dextran sodium sulfate-induced colitis. Altogether, this study reveals that IL-15 impacts butyrate-producing bacteria and lowers butyrate levels in the absence of overt pathology, which represent events that precede and promote intestinal inflammatory diseases.

Suppressor of Cytokine Signaling-1 Peptidomimetic Limits Progression of Diabetic Nephropathy

Diabetes is the main cause of CKD and ESRD worldwide. Chronic activation of Janus kinase and signal transducer and activator of transcription (STAT) signaling contributes to diabetic nephropathy by inducing genes involved in leukocyte infiltration, cell proliferation, and extracellular matrix accumulation. This study examined whether a cell-permeable peptide mimicking the kinase-inhibitory region of suppressor of cytokine signaling-1 (SOCS1) regulatory protein protects against nephropathy by suppressing STAT-mediated cell responses to diabetic conditions. In a mouse model combining hyperglycemia and hypercholesterolemia (streptozotocin diabetic, apoE-deficient mice), renal STAT activation status correlated with the severity of nephropathy. Notably, compared with administration of vehicle or mutant inactive peptide, administration of the SOCS1 peptidomimetic at either early or advanced stages of diabetes ameliorated STAT activity and resulted in reduced serum creatinine level, albuminuria, and renal histologic changes (mesangial expansion, tubular injury, and fibrosis) over time. Mice treated with the SOCS1 peptidomimetic also exhibited reduced kidney leukocyte recruitment (T lymphocytes and classic M1 proinflammatory macrophages) and decreased expression levels of proinflammatory and profibrotic markers that were independent of glycemic and lipid changes. In vitro, internalized peptide suppressed STAT activation and target gene expression induced by inflammatory and hyperglycemic conditions, reduced migration and proliferation in mesangial and tubuloepithelial cells, and altered the expression of cytokine-induced macrophage polarization markers. In conclusion, our study identifies SOCS1 mimicking as a feasible therapeutic strategy to halt the onset and progression of renal inflammation and fibrosis in diabetic kidney disease.

Interleukin 15: A key cytokine for immunotherapy

Interleukin (IL)-15, a member of the immunoregulatory cytokines family, is a pluripotent molecule with therapeutic potential. It is predominantly expressed by the myeloid cells, as well as other cell types. IL-15 serves multiple functions including dictating T cell response, regulating tissue repair and B cell homing, modulating inflammation, and activating NK cells. Among cytokines, IL-15 is unique because of its wide expression, tightly regulated secretion, trans-presentation, and therapeutic potential. IL-15 has been investigated for its therapeutic potential for the induction and maintenance of T cell responses. In addition, IL-15 can be targeted by antibody- or mutant IL-15 therapy to reduce inflammation. Its multifaceted biological applications are crucial in immunotherapy. In this article, we review the functions, expression, and regulation of IL-15 for designing an improved IL-15-based therapy targeting the IL-15 signaling pathway.

Trans-presentation of interleukin-15 by interleukin-15 receptor alpha is dispensable for the pathogenesis of autoimmune type 1 diabetes

Interleukin-15 (IL-15) is a pro-inflammatory cytokine that is required for the survival and activation of memory CD8⁺T cells, natural killer (NK) cells, innate lymphoid cells, macrophages and dendritic cells. IL-15 is implicated in the pathogenesis of various autoimmune diseases such as rheumatoid arthritis, inflammatory bowel disease, psoriasis and autoimmune type 1 diabetes (T1D). IL-15 receptor (IL-15R) consists of a specific α chain, the β chain that is shared with IL-2R and the common γ chain. IL-15 is unique in the manner in which it binds and signals through its receptor subunits. IL-15 that is complexed with IL-15Rα binds to the βγ receptor complex present on the responding cell to mediate its biological effects through a process referred to as trans-presentation. The trans-presented IL-15 is essential to mediate the biological effects on T lymphocytes and NK cells. Here we show that IL-15, but not IL-15Rα, is required for the development of spontaneous and virus-induced T1D, viral clearance and for antigen cross-presentation to CD8⁺ T lymphocytes. Our findings provide insight into the complexities of IL-15 signalling in the initiation and maintenance of CD8⁺ T cell-mediated immune responses.

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.

Distinct and Synergistic Contributions of Epithelial Stress and Adaptive Immunity to Functions of Intraepithelial Killer Cells and Active Celiac Disease

BACKGROUND & AIMS

The mechanisms of tissue destruction during progression of celiac disease are poorly defined. It is not clear how tissue stress and adaptive immunity contribute to the activation of intraepithelial cytotoxic T cells and the development of villous atrophy. We analyzed epithelial cells and intraepithelial cytotoxic T cells in family members of patients with celiac disease, who were without any signs of adaptive antigluten immunity, and in potential celiac disease patients, who have antibodies against tissue transglutaminase 2 in the absence of villous atrophy.

METHODS

We collected blood and intestinal biopsy specimens from 268 patients at tertiary medical centers in the United States and Italy from 2004 to 2012. All subjects had normal small intestinal histology. Study groups included healthy individuals with no family history of celiac disease or antibodies against tissue transglutaminase 2 (controls), healthy family members of patients with celiac disease, and potential celiac disease patients. Intraepithelial cytotoxic T cells were isolated and levels of inhibitory and activating natural killer (NK) cells were measured by flow cytometry. Levels of heat shock protein (HSP) and interleukin 15 were measured by immunohistochemistry, and ultrastructural alterations in intestinal epithelial cells (IECs) were assessed by electron microscopy.

RESULTS

IECs from subjects with a family history of celiac disease, but not from subjects who already had immunity to gluten, expressed higher levels of HS27, HSP70, and interleukin-15 than controls; their IECs also had ultrastructural alterations. Intraepithelial cytotoxic T cells from relatives of patients with celiac disease expressed higher levels of activating NK receptors than cells from controls, although at lower levels than patients with active celiac disease, and without loss of inhibitory receptors for NK cells. Intraepithelial cytotoxic T cells from potential celiac disease patients failed to up-regulate activating NK receptors.

CONCLUSIONS

A significant subset of healthy family members of patients with celiac disease with normal intestinal architecture had epithelial alterations, detectable by immunohistochemistry and electron microscopy. The adaptive immune response to gluten appears to act in synergy with epithelial stress to allow intraepithelial cytotoxic T cells to kill epithelial cells and induce villous atrophy in patients with active celiac disease.

Cysteinyl leukotrienes mediate lymphokine killer activity induced by NKG2D and IL-15 in cytotoxic T cells during celiac disease

Tang et al. show that cytotoxic effector cells produce and respond to cysteinyl leukotrienes to allow target cell killing dependent on NKG2D and IL-15. They further demonstrate a role for cysteinyl leukotrienes in celiac disease pathogenesis.

Eicosanoids are inflammatory mediators that play a key but incompletely understood role in linking the innate and adaptive immune systems. Here, we show that cytotoxic effector T cells (CTLs) are capable of both producing and responding to cysteinyl leukotrienes (CystLTs), allowing for the killing of target cells in a T cell receptor–independent manner. This process is dependent on the natural killer receptor NKG2D and exposure to IL-15, a cytokine induced in distressed tissues. IL-15 and NKG2D signaling drives the up-regulation of key enzymes implicated in the synthesis of CystLTs, as well as the expression of CystLT receptors, suggesting a positive feedback loop. Finally, although the CystLT pathway has been previously linked to various allergic disorders, we provide unexpected evidence for its involvement in the pathogenesis of celiac disease (CD), a T helper 1 cell–mediated enteropathy induced by gluten. These findings provide new insights into the cytolytic signaling pathway of NKG2D and the pathogenesis of organ-specific immune disorders. Furthermore, they suggest that the blockade of CystLT receptors may represent a potent therapeutic target for CD or potentially other autoimmune disorders in which NKG2D has been implicated.

A run on the biobank: what have we learned about type 1 diabetes from the nPOD tissue repository?

PURPOSE OF REVIEW

Since the inaugural year of its biobank in 2007, the Network for Pancreatic Organ Donors with Diabetes program has provided 70 370 human samples to 127 investigators worldwide for projects focused on the pathogenesis of type 1 diabetes (T1D). The purpose of this review was to highlight major advances in our understanding of T1D using works that contain original data from experiments utilizing biospecimens provided by the Network for Pancreatic Organ Donors with Diabetes program. A total of 15 studies, published between 1 June 2013 and 31 December 2014, were selected using various search and filter strategies.

RECENT FINDINGS

The type and frequency of B and/or T-cell immune markers in both the endocrine and exocrine compartments vary in T1D. Enterovirus signals have been identified as having new proteins in the extracellular matrix around infiltrated islets. Novel genes within human islet cell types have been shown to play a role in immunity, infiltration, inflammation, disease progression, cell mass and function. Various cytokines and a complement degradation product have also been detected in the blood or surrounding pancreatic ducts/vasculature.

SUMMARY

These findings, from T1D donors across the disease spectrum, emphasize the notion that pathogenic heterogeneity is a hallmark of the disorder.

Exercise-stimulated interleukin-15 is controlled by AMPK and regulates skin metabolism and aging

Aging is commonly associated with a structural deterioration of skin that compromises its barrier function, healing, and susceptibility to disease. Several lines of evidence show that these changes are driven largely by impaired tissue mitochondrial metabolism. While exercise is associated with numerous health benefits, there is no evidence that it affects skin tissue or that endocrine muscle-to-skin signaling occurs. We demonstrate that endurance exercise attenuates age-associated changes to skin in humans and mice and identify exercise-induced IL-15 as a novel regulator of mitochondrial function in aging skin. We show that exercise controls IL-15 expression in part through skeletal muscle AMP-activated protein kinase (AMPK), a central regulator of metabolism, and that the elimination of muscle AMPK causes a deterioration of skin structure. Finally, we establish that daily IL-15 therapy mimics some of the anti-aging effects of exercise on muscle and skin in mice. Thus, we elucidate a mechanism by which exercise confers health benefits to skin and suggest that low-dose IL-15 therapy may prove to be a beneficial strategy to attenuate skin aging.

Innate immunity: actuating the gears of celiac disease pathogenesis

Celiac disease is a T cell mediated immune disorder characterized by the loss of oral tolerance to dietary gluten and the licensing of intraepithelial lymphocytes to kill intestinal epithelial cells, leading to villous atrophy. Innate immunity plays a critical role in both of these processes and cytokines such as interleukin-15 and interferon-α can modulate innate processes such as polarization of dendritic cells as well as intraepithelial lymphocyte function. These cytokines can be modulated by host microbiota, which can also influence dendritic cell function and intraepithelial lymphocyte homeostasis. We will elaborate on the role of interleukin-15, interferon-α, and the microbiota in modulating the processes that lead to loss of tolerance to gluten and tissue destruction in celiac disease.

Rodent versus human insulitis: why the huge disconnect?

PURPOSE OF REVIEW

The purpose of this article is to summarize recent developments in the histopathology of recent-onset type 1 diabetes.

RECENT FINDINGS

Insulitis is considered to be the defining lesion in young type 1 diabetic patients, and insight into its pathogenic mechanism is crucial for the development of effective new therapies. The present overview highlights some recent developments including an international consensus guideline for the diagnosis of insulitis in type 1 diabetic patients, immunophenotyping of the insulitic lesions, evidence for a heterogeneity of the disease process and a discussion on the differences and similarities between insulitis in patients and in rodent models of the disease.

SUMMARY

We have reviewed recent data, published over the last year, on the nature and mechanism of insulitis in both patients and the nonobese diabetic mouse model.

IL-15-dependent CD8+ CD122+ T cells ameliorate experimental autoimmune encephalomyelitis by modulating IL-17 production by CD4+ T cells

Interleukin-15 (IL-15) is an inflammatory cytokine whose role in autoimmune diseases has not been fully elucidated. Th17 cells have been shown to play critical roles in experimental autoimmune encephalomyelitis (EAE) models. In this study, we demonstrate that blockade of IL-15 signaling by TMβ-1 mAb treatment aggravated EAE severity. The key mechanism was not NK-cell depletion but depletion of CD8+ CD122+ T cells. Adoptive transfer of exogenous CD8+ CD122+ T cells to TMβ-1-treated mice rescued animals from severe disease. Moreover, transfer of preactivated CD8+ CD122+ T cells prevented EAE development and significantly reduced IL-17 secretion. Naïve effector CD4+ CD25- T cells cultured with either CD8+ CD122+ T cells from wild-type mice or IL-15 transgenic mice displayed lower frequencies of IL-17A production with lower amounts of IL-17 in the supernatants when compared with production by effector CD4+ CD25- T cells cultured alone. Addition of a neutralizing antibody to IL-10 led to recovery of IL-17A production in Th17 cultures. Furthermore, coculture of CD8+ CD122+ T cells with effector CD4+ T cells inhibited their proliferation significantly, suggesting a regulatory function for IL-15 dependent CD8+ CD122+ T cells. Taken together, these observations suggest that IL-15, acting through CD8+ CD122+ T cells, has a negative regulatory role in reducing IL-17 production and Th17-mediated EAE inflammation.

IL-15: a central regulator of celiac disease immunopathology

Interleukin-15 (IL-15) exerts many biological functions essential for the maintenance and function of multiple cell types. Although its expression is tightly regulated, IL-15 upregulation has been reported in many organ-specific autoimmune disorders. In celiac disease, an intestinal inflammatory disorder driven by gluten exposure, the upregulation of IL-15 expression in the intestinal mucosa has become a hallmark of the disease. Interestingly, because it is overexpressed both in the gut epithelium and in the lamina propria, IL-15 acts on distinct cell types and impacts distinct immune components and pathways to disrupt intestinal immune homeostasis. In this article, we review our current knowledge of the multifaceted roles of IL-15 with regard to the main immunological processes involved in the pathogenesis of celiac disease.