Jak3 negatively regulates dendritic-cell cytokine production and survival

Plasmacytoid dendritic cells at the forefront of anti-cancer immunity: rewiring strategies for tumor microenvironment remodeling

Plasmacytoid dendritic cells (pDCs) are multifaceted immune cells executing various innate immunological functions. Their first line of defence consists in type I interferons (I-IFN) production upon nucleic acids sensing through endosomal Toll-like receptor (TLR) 7- and 9-dependent signalling pathways. Type I IFNs are a class of proinflammatory cytokines that have context-dependent functions on cancer immunosurveillance and immunoediting. In the last few years, different studies have reported that pDCs are also able to sense cytosolic DNA through cGAS-STING (stimulator of interferon genes) pathway eliciting a potent I-IFN production independently of TLR7/9. Human pDCs are also endowed with direct effector functions via the upregulation of TRAIL and production of granzyme B, the latter modulated by cytokines abundant in cancer tissues. pDCs have been detected in a wide variety of human malignant neoplasms, including virus-associated cancers, recruited by chemotactic stimuli. Although the role of pDCs in cancer immune surveillance is still uncompletely understood, their spontaneous activation has been rarely documented; moreover, their presence in the tumor microenvironment (TME) has been associated with a tolerogenic phenotype induced by immunosuppressive cytokines or oncometabolites. Currently tested treatment options can lead to pDCs activation and disruption of the immunosuppressive TME, providing a relevant clinical benefit. On the contrary, the antibody-drug conjugates targeting BDCA-2 on immunosuppressive tumor-associated pDCs (TA-pDCs) could be proposed as novel immunomodulatory therapies to achieve disease control in patients with advance stage hematologic malignancies or solid tumors. This Review integrate recent evidence on the biology of pDCs and their pharmacological modulation, suggesting their relevant role at the forefront of cancer immunity.

Plasmacytoid dendritic cells: A dendritic cell in disguise

Since their discovery, the identity of plasmacytoid dendritic cells (pDCs) has been at the center of a continuous dispute in the field, and their classification as dendritic cells (DCs) has been recently re-challenged. pDCs are different enough from the rest of the DC family members to be considered a lineage of cells on their own. Unlike the exclusive myeloid ontogeny of cDCs, pDCs may have dual origin developing from myeloid and lymphoid progenitors. Moreover, pDCs have the unique ability to quickly secrete abundant levels of type I interferon (IFN-I) in response to viral infections. In addition, pDCs undergo a differentiation process after pathogen recognition that allows them to activate T cells, a feature that has been shown to be independent of presumed contaminating cells. Here, we aim to provide an overview of the historic and current understanding of pDCs and argue that their classification as either lymphoid or myeloid may be an oversimplification. Instead, we propose that the capacity of pDCs to link the innate and adaptive immune response by directly sensing pathogens and activating adaptive immune responses justify their inclusion within the DC network.

Selective Inhibitors of Janus Kinase 3 Modify Responses to Lipopolysaccharides by Increasing the Interleukin-10-to-Tumor Necrosis Factor α Ratio

Janus kinase (JAK) inhibitors act at low doses (e.g., tofacitinib, 0.2-0.4 μmol/kg bid) in clinical use, suggesting an efficient underlying mode of action. We hypothesized that their effectiveness is due to their ability to raise the ratio of IL-10 to TNFα. Unlike other JAK isoforms, JAK3 is expressed mainly in hematopoietic cells and is essential for immune function. We used JAK3 selective inhibitors with preferential distribution to immune cells. Inhibition of JAK3 in human leukocytes reduced TNFα and IL-6 but maintained levels of IL-10, while pan-JAK inhibitors increased TNFα, IL-6, and IL-10. JAK1 is required for IL-10 receptor signaling, which suggests that, at exposure above the IC50 (55 nM for tofacitinib on JAK1), there is less feedback control of TNFα levels. This leads to self-limiting effects of JAK1 inhibitors and could place an upper limit on appropriate doses. In vivo, treating mice with JAK3 inhibitors before LPS administration decreased plasma TNFα and increased IL-10 above vehicle levels, suggesting that JAK3 inhibition may limit TNFα release by increasing IL-10 while leaving the IL-10 receptor functional. This mechanism should have general utility in controlling autoimmune diseases and can be conveniently observed by measuring the ratio of IL-10 to TNFα. In summary, our targeted, "leukotropic" inhibitors more effectively increased IL-10/TNFα ratios than unselective control compounds and could, therefore, be ideal for autoimmune therapy.

JAK1 signaling in dendritic cells promotes peripheral tolerance in autoimmunity through PD-L1-mediated regulatory T cell induction

Dendritic cells (DCs) induce peripheral T cell tolerance, but cell-intrinsic signaling cascades governing their stable tolerogenesis remain poorly defined. Janus Kinase 1 (JAK1) transduces cytokine-receptor signaling, and JAK inhibitors (Jakinibs), including JAK1-specific filgotinib, break inflammatory cycles in autoimmunity. Here, we report in heterogeneous DC populations of multiple secondary lymphoid organs that JAK1 promotes peripheral T cell tolerance during experimental autoimmune encephalomyelitis (EAE). Mice harboring DC-specific JAK1 deletion exhibit elevated peripheral CD4+ T cell expansion, less regulatory T cells (Tregs), and worse EAE outcomes, whereas adoptive DC transfer ameliorates EAE pathogenesis by inducing peripheral Tregs, programmed cell death ligand 1 (PD-L1) dependently. This tolerogenic program is substantially reduced upon the transfer of JAK1-deficient DCs. DC-intrinsic IFN-γ-JAK1-STAT1 signaling induces PD-L1, which is required for DCs to convert CD4+ T cells into Tregs in vitro and attenuated upon JAK1 deficiency and filgotinib treatment. Thus, DC-intrinsic JAK1 promotes peripheral tolerance, suggesting potential unwarranted DC-mediated effects of Jakinibs in autoimmune diseases.

Spontaneous Posterior Segment Vascular Disease Phenotype of a Mouse Model, rnv3, Is Dependent on the Crb1rd8 Allele

Purpose

To determine the molecular basis of lesion development in a murine model of spontaneous retinal vascularization, rnv3 (retinal vascularization 3, aka JR5558).

Methods

Disease progression of rnv3 was examined in longitudinal studies by clinical evaluation, electroretinography (ERG) and light microscopy analyses. The chromosomal position for the recessive rnv3 mutation was determined by DNA pooling and genome-wide linkage analysis. The causative mutation was discovered by comparison of whole exome sequences of rnv3 mutant and wild-type (WT) controls. In order to confirm the causative mutation, transcription activator-like effector nuclease (TALEN)-mediated oligonucleotide directed repair (ODR) was utilized to correct the mutant allele. Phenotypic correction was assessed by fundus imaging and optical coherence tomography of live mice.

Results

rnv3 exhibits early-onset, multifocal depigmented retinal lesions observable by fundus examination starting at 18 days of age. The retinal lesions are associated with fluorescein leakage around 25 days of age, with peak leakage at about 4 weeks of age. ERG responses deteriorate as rnv3 mutants age, concomitant with progressive photoreceptor disruption and loss that is observable by histology. Genetic analysis localized rnv3 to mouse chromosome (Chr) 1. By high throughput sequencing of a whole exome capture library of a rnv3/rnv3 mutant and subsequent sequence analysis, a single base deletion (del) in the Crb1 [crumbs family member 1] gene, which was previously reported to cause retinal degeneration 8, was identified. The TALEN-mediated ODR rescued the posterior segment vascularization phenotype; heterozygous Crb1^rd8+em1Boc/Crb1^rd8 and homozygous Crb1^rd8+em1Boc/Crb1^rd8+em1Boc mice showed a normal retinal phenotype. Additionally, six novel disruptions of Crb1 that were generated through aberrant non-homologous end joining induced by TALEN exhibited variable levels of vascularization, suggesting allelic effects.

Conclusions

The rnv3 model and the models of six novel disruptions of Crb1 are all reliable, novel mouse models for the study of both early and late events associated with posterior segment vascularization and can also be used to test the effects of pharmacological targets for treating human ocular vascular disorders. Further study of these models may provide a greater understanding about how different Crb1 alleles result in aberrant angiogenesis.

Signal transducer and activator of transcription 5 (STAT5) paralog dose governs T cell effector and regulatory functions

The transcription factor STAT5 is fundamental to the mammalian immune system. However, the relationship between its two paralogs, STAT5A and STAT5B, and the extent to which they are functionally distinct, remain uncertain. Using mouse models of paralog deficiency, we demonstrate that they are not equivalent for CD4⁺ 'helper' T cells, the principal orchestrators of adaptive immunity. Instead, we find that STAT5B is dominant for both effector and regulatory (Treg) responses and, therefore, uniquely necessary for immunological tolerance. Comparative analysis of genomic distribution and transcriptomic output confirm that STAT5B has fargreater impact but, surprisingly, the data point towards asymmetric expression (i.e. paralog dose), rather than distinct functional properties, as the key distinguishing feature. Thus, we propose a quantitative model of STAT5 paralog activity whereby relative abundance imposes functional specificity (or dominance) in the face of widespread structural homology.

DOI:http://dx.doi.org/10.7554/eLife.08384.001

The immune system in mammals is one of the most complex networks in the animal kingdom. One way that its many components communicate is via proteins called cytokines, which are released by cells and detected by receptors on the surface of other cells. This leads to the activation of signals inside the responding cells that alter the activity of genes and, ultimately, direct how they behave.

STAT5 is a signal protein that is activated when certain cytokines bind to receptors on the cell surface. Consequently, it is an attractive target for drug therapies that seek to alter immune responses and there is keen interest in understanding how it works. It is an unusual protein in that there are two versions – termed STAT5A and STAT5B – that are produced by two separate genes. Together, STAT5A and STAT5B are fundamental to the immune system but there is considerable debate about whether they perform the same job or have distinct roles.

Villarino et al. used a combination of genetic and genomic approaches to investigate how both versions of STAT5 work in mice. The experiments show that STAT5B plays a much bigger role in immune cells than STAT5A. Unexpectedly, the experiments indicate that the disparity is not due to differences in protein activity, but is caused by differences in the amount of these proteins in cells.

Villarino et al.’s findings resolve longstanding questions about the relationship between STAT5A and STAT5B within the immune system. A logical next step is to find the molecular mechanisms responsible for causing different amounts of STAT5A and STAT5B to be produced in immune cells. Future work will also compare the roles of STAT5A and STAT5B in non-immune cells and explore whether it might be possible to develop therapies that specifically target one version and not the other.

DOI:http://dx.doi.org/10.7554/eLife.08384.002

Janus kinase 3 regulates renal 25-hydroxyvitamin D 1α-hydroxylase expression, calcitriol formation, and phosphate metabolism

Calcitriol, a powerful regulator of phosphate metabolism and immune response, is generated by 25-hydroxyvitamin D 1α-hydroxylase in the kidney and macrophages. Renal 1α-hydroxylase expression is suppressed by Klotho and FGF23, the expression of which is stimulated by calcitriol. Interferon γ (INFγ) regulates 1α-hydroxylase expression in macrophages through transcription factor interferon regulatory factor-1. INFγ-signaling includes Janus kinase 3 (JAK3) but a role of JAK3 in the regulation of 1α-hydroxylase expression and mineral metabolism has not been shown. Thus, the impact of JAK3 deficiency on calcitriol formation and phosphate metabolism was measured. Renal interferon regulatory factor-1 and 1α-hydroxylase transcript levels, serum calcitriol and FGF23 levels, intestinal phosphate absorption as well as absolute and fractional renal phosphate excretion were significantly higher in jak3 knockout than in wild-type mice. Coexpression of JAK3 increased the phosphate-induced current in renal sodium-phosphate cotransporter-expressing Xenopus oocytes. Thus, JAK3 is a powerful regulator of 1α-hydroxylase expression and phosphate transport. Its deficiency leads to marked derangement of phosphate metabolism.

Upregulation of excitatory amino acid transporters by coexpression of Janus kinase 3

Janus kinase 3 (JAK3) contributes to cytokine receptor signaling, confers cell survival and stimulates cell proliferation. The gain of function mutation JAK3(A572V) is found in acute megakaryoplastic leukemia. Replacement of ATP coordinating lysine by alanine yields inactive JAK3(K855A). Most recent observations revealed the capacity of JAK3 to regulate ion transport. This study thus explored whether JAK3 regulates glutamate transporters EAAT1-4, carriers accomplishing transport of glutamate and aspartate in a variety of cells including intestinal cells, renal cells, glial cells, and neurons. To this end, EAAT1, 2, 3, or 4 were expressed in Xenopus oocytes with or without additional expression of mouse wild-type JAK3, constitutively active JAK3(A568V) or inactive JAK3(K851A), and electrogenic glutamate transport was determined by dual electrode voltage clamp. Moreover, Ussing chamber was employed to determine electrogenic glutamate transport in intestine from mice lacking functional JAK3 (jak3(-/-)) and from corresponding wild-type mice (jak3(+/+)). As a result, in EAAT1, 2, 3, or 4 expressing oocytes, but not in oocytes injected with water, addition of glutamate to extracellular bath generated an inward current (Ig), which was significantly increased following coexpression of JAK3. Ig in oocytes expressing EAAT3 was further increased by JAK3(A568V) but not by JAK3(K851A). Ig in EAAT3 + JAK3 expressing oocytes was significantly decreased by JAK3 inhibitor WHI-P154 (22 µM). Kinetic analysis revealed that JAK3 increased maximal Ig and significantly reduced the glutamate concentration required for half maximal Ig (Km). Intestinal electrogenic glutamate transport was significantly lower in jak3(-/-) than in jak3(+/+) mice. In conclusion, JAK3 is a powerful regulator of excitatory amino acid transporter isoforms.

IL-23R+ innate lymphoid cells induce colitis via interleukin-22-dependent mechanism

Polymorphisms of interleukin (IL)-23R and signaling components are associated with several autoimmune diseases, including inflammatory bowel diseases (IBD). Similar to T helper type 17 (Th17) lineage, type 3 innate lymphoid cells (ILCs) express retinoic acid-related orphan receptor γt (Rorγt) and IL-23R and hence, produce Th17-type cytokines. Recent reports implicated type 3 ILCs in IBD; however, how IL-23R signaling in these cells contributes to pathogenesis is unknown. IL-22, produced in copious amounts by type 3 ILCs, was reported to have both beneficial and pathogenic effects in adaptive, yet only a protective role in innate colitis models. Herein, by employing chronic CD45RB(high) CD4(+) T-cell transfer and anti-CD40 antibody-induced acute innate colitis models in Rag1(-/-) mice, we demonstrated opposite roles for IL-23R in colitogenesis: in the former a protective, and in the latter a pathogenic role. Furthermore, we show that IL-23R signaling promotes innate colitis via IL-22 as neutralization of IL-22 protected mice from colitis and adding back of IL-22 to IL-23R-deficient animals restored the disease. Collectively, our results reveal that similar to its controversial role during chronic or adaptive colitis, IL-22 may also have opposite roles in innate colitis pathogenesis in a context and insult-dependent manner.

Intestinal Na+ loss and volume depletion in JAK3-deficient mice

BACKGROUND/AIMS

The Janus kinase 3 JAK3 participates in the signaling of immune cells. Lack of JAK3 triggers inflammatory bowel disease, which in turn has been shown to affect intestinal activity of the epithelial Na(+) channel ENaC and thus colonic sodium absorption. At least in theory, inflammatory bowel disease in JAK3-deficient mice could lead to intestinal salt loss compromizing extracellular volume maintenance and blood pressure regulation. The present study thus explored whether JAK3 deficiency impacts on colonic ENaC activity, fecal Na(+) exretion, blood pressure and extracellular fluid volume regulation.

METHODS

Experiments were performed in gene-targeted mice lacking functional JAK3 (jak3(-/-)) and in wild type mice (jak3(+/+)). Colonic ENaC activity was estimated from amiloride-sensitive current in Ussing chamber experiments, fecal, serum and urinary Na(+) concentration by flame photometry, blood pressure by the tail cuff method and serum aldosterone levels by immunoassay.

RESULTS

The amiloride (50 µM)-induced deflection of the transepithelial potential difference was significantly lower and fecal Na(+) excretion significantly higher in jak3(-/-) mice than in jak3(+/+) mice. Moreover, systolic arterial blood pressure was significantly lower and serum aldosterone concentration significantly higher in jak3(-/-) mice than in jak3(+/+) mice. Both, absolute and fractional renal Na(+) excretion were significantly lower in jak3(-/-) mice than in jak3(+/+) mice.

CONCLUSIONS

JAK3 deficiency leads to impairment of colonic ENaC activity with intestinal Na(+) loss, decrease of blood pressure, increased aldosterone release and subsequent stimulation of renal tubular Na(+) reabsorption.

The role of JAK-3 in regulating TLR-mediated inflammatory cytokine production in innate immune cells

The role of JAK-3 in TLR-mediated innate immune responses is poorly understood, although the suppressive function of JAK3 inhibition in adaptive immune response has been well studied. In this study, we found that JAK3 inhibition enhanced TLR-mediated immune responses by differentially regulating pro- and anti- inflammatory cytokine production in innate immune cells. Specifically, JAK3 inhibition by pharmacological inhibitors or specific small interfering RNA or JAK3 gene knockout resulted in an increase in TLR-mediated production of proinflammatory cytokines while concurrently decreasing the production of IL-10. Inhibition of JAK3 suppressed phosphorylation of PI3K downstream effectors including Akt, mammalian target of rapamycin complex 1, glycogen synthase kinase 3β (GSK3β), and CREB. Constitutive activation of Akt or inhibition of GSK3β abrogated the capability of JAK3 inhibition to enhance proinflammatory cytokines and suppress IL-10 production. In contrast, inhibition of PI3K enhanced this regulatory ability of JAK3 in LPS-stimulated monocytes. At the transcriptional level, JAK3 knockout lead to the increased phosphorylation of STATs that could be attenuated by neutralization of de novo inflammatory cytokines. JAK3 inhibition exhibited a GSK3 activity-dependent ability to enhance phosphorylation levels and DNA binding of NF-κB p65. Moreover, JAK3 inhibition correlated with an increased CD4(+) T cell response. Additionally, higher neutrophil infiltration, IL-17 expression, and intestinal epithelium erosion were observed in JAK3 knockout mice. These findings demonstrate the negative regulatory function of JAK3 and elucidate the signaling pathway by which JAK3 differentially regulates TLR-mediated inflammatory cytokine production in innate immune cells.

JAK inhibitor tofacitinib for treating rheumatoid arthritis: from basic to clinical

Rheumatoid arthritis (RA) is a representative autoimmune disease characterized by chronic and destructive inflammatory synovitis. The multiple cytokines play pivotal roles in RA pathogenesis by inducing intracellular signaling, and members of the Janus kinase (JAK) family are essential for such signal transduction. An orally available JAK3 inhibitor, tofacitinib, has been applied for RA, with satisfactory effects and acceptable safety in multiple clinical examinations. From phase 2 dose-finding studies, tofacitinib 5 mg and 10 mg twice a day appear suitable for further evaluation. Subsequently, multiple phase 3 studies were carried out, and tofacitinib with or without methotrexate (MTX) is efficacious and has a manageable safety profile in active RA patients who are MTX naïve or show inadequate response to methotrexate (MTX-IR), disease-modifying antirheumatic drugs (DMARD)-IR, or tumor necrosis factor (TNF)-inhibitor-IR. The common adverse events were infections, such as nasopharyngitis; increases in cholesterol, transaminase, and creatinine; and decreases in neutrophil counts. Although the mode of action of tofacitinib remains unclear, we clarified that the inhibitory effects of tofacitinib could be mediated through suppression of interleukin (IL)-17 and interferon (IFN)-γ production and proliferation of CD4(+) T cells in the inflamed synovium. Taken together, an orally available kinase inhibitor tofacitinib targeting JAK-mediated signals would be expected to be a new option for RA treatment.

Suppressor of cytokine signaling 1 DNA administration inhibits inflammatory and pathogenic responses in autoimmune myocarditis

Myocarditis and subsequent dilated cardiomyopathy are major causes of heart failure in young adults. Myocarditis in humans is highly heterogeneous in etiology. Recent studies have indicated that a subgroup of myocarditis patients may benefit from immune-targeted therapies, because autoimmunity plays an important role in myocarditis as well as contributing to the progression to cardiomyopathy and heart failure. Suppressor of cytokine signaling (SOCS) 1 plays a key role in the negative regulation of both TLR- and cytokine receptor-mediated signaling, which is involved in innate immunity and subsequent adaptive immunity. In this study, we investigated the therapeutic effect of SOCS1 DNA administration on experimental autoimmune myocarditis (EAM) in mice. EAM was induced by s.c. immunization with cardiac-specific peptides derived from α myosin H chain in BALB/c mice. In contrast to control myocarditis mice, SOCS1 DNA-injected mice were protected from development of EAM and heart failure. SOCS1 DNA administration was effective for reducing the activation of autoreactive CD4(+) T cells by inhibition of the function of Ag-presenting dendritic cells. Our findings suggest that SOCS1 DNA administration has considerable therapeutic potential in individuals with autoimmune myocarditis and dilated cardiomyopathy.

[Regulation of inflammation through JAK3-Stat6 pathway in dendritic cells]

Dendritic cells (DCs) is the cell that act as source of the immune response by exquisitely presenting antigens to acquired immunity such as the T cells. Janus kinase (JAK) is a tyrosine kinase that is activated immediately after the cytokine binds to its unique receptor expressed on the cell surface. Among the JAKs, expression of JAK3 is limited on haematopoietic cells and is indispensable for lymphocyte development and proliferation. We have demonstrated that JAK3-deficient DCs normally develop, uptake antigens, produce inflammatory cytokines and function as an antigen-presenting cell, although they over-produce IL-10. Among the transcription factors that are known to be activated by JAK3, we explored the phenotype of Stat6-deficient DCs which is a transcription factor specifically activated by JAK3. Interestingly, development, function and inflammatory cytokine production was normal with over-production of IL-10 which was in line with the JAK3-deficient DCs. IL-4 is well known to activate JAK3-Stat6 in the cytoplasm and has been reported to be produced in the synovial fluid of rheumatoid arthritis patients. Hence the suppression of IL-10 production by IL-4 can be considered as one of the inflammatory process of arthritis. Moreover, induction of IL-10 production by DCs can be one mechanism of action of the JAK inhibitor (tofacitinib) which have shown high efficiency on active rheumatoid arthritis in clinical trials.

Expression and function of interleukin-7 in secondary and tertiary lymphoid organs

Interleukin-7 (IL-7) is known since many years as stromal-cell derived cytokine that plays a key role for the adaptive immune system. It promotes lymphocyte development in the bone marrow and thymus as well as naive and memory T cell homeostasis in the periphery. More recently, IL-7 reporter mice and other approaches have led to the further characterization of the various stromal cell sources of IL-7 in secondary lymphoid organs (SLO) and other tissues. We will review these advances along with a discussion of the regulation of IL-7 and its receptor, and compare the biological effects IL-7 has on adaptive as well as innate immune cells in SLO. Finally, we will review the role of IL-7 in development of SLO and tertiary lymphoid tissues that frequently are associated with sites of chronic inflammation.

The JAK inhibitor tofacitinib regulates synovitis through inhibition of interferon-γ and interleukin-17 production by human CD4+ T cells

OBJECTIVE

Tofacitinib (CP-690,550) is a novel JAK inhibitor that is currently in clinical trials for the treatment of rheumatoid arthritis (RA). The aim of this study was to examine the effects of tofacitinib in vitro and in vivo in RA, in order to elucidate the role of JAK in the disease process.

METHODS

CD4+ T cells, CD14+ monocytes, and synovial fibroblasts (SFs) were purified from the synovium and peripheral blood of patients with RA and were evaluated for the effect of tofacitinib on cytokine production and cell proliferation. For in vivo analysis, synovium and cartilage samples obtained from patients with RA were implanted in immunodeficient mice (SCID-HuRAg mice), and tofacitinib was administered via an osmotic minipump.

RESULTS

Tofacitinib treatment of CD4+ T cells originating from synovium and peripheral blood inhibited the production of interleukin-17 (IL-17) and interferon-γ (IFNγ) in a dose-dependent manner, affecting both proliferation and transcription, but had no effect on IL-6 and IL-8 production. Tofacitinib did not affect IL-6 and IL-8 production by RASFs and CD14+ monocytes. However, conditioned medium from CD4+ T cells cultured with tofacitinib inhibited IL-6 production by RASFs and IL-8 production by CD14+ monocytes. Treatment of SCID-HuRAg mice with tofacitinib decreased serum levels of human IL-6 and IL-8 and markedly suppressed invasion of synovial tissue into cartilage.

CONCLUSION

Tofacitinib directly suppressed the production of IL-17 and IFNγ and the proliferation of CD4+ T cells, resulting in inhibition of IL-6 production by RASFs and IL-8 production by CD14+ cells and decreased cartilage destruction. In CD4+ T cells, presumably Th1 and Th17 cells, JAK plays a crucial role in RA synovitis.

Janus kinase 3 is expressed in erythrocytes, phosphorylated upon energy depletion and involved in the regulation of suicidal erythrocyte death

Janus kinase 3, a tyrosine kinase expressed in haematopoetic tissues, plays a decisive role in T-lymphocyte survival. JAK3 deficiency leads to (Severe) Combined Immunodeficiency (SCID) resulting from enhanced lymphocyte apoptosis. JAK3 is activated by phosphorylation. Nothing is known about expression of JAK3 in erythrocytes, which may undergo apoptosis-like cell death (eryptosis) characterized by cell membrane scrambling with phosphatidylserine exposure and cell shrinkage. Triggers of eryptosis include energy depletion. The present study utilized immunohistochemistry and confocal microscopy to test for JAK3 expression and phosphorylation, and FACS analysis to determine phosphatidylserine exposure (annexin binding) and cell volume (forward scatter). As a result, JAK3 was expressed in erythrocytes and phosphorylated following 24h and 48h glucose depletion. Forward scatter was slightly but significantly smaller in erythrocytes from JAK3-deficient mice (jak3(-/-)) than in erythrocytes from wild type mice (jak3(+/+)). Annexin V binding was similarly low in both genotypes. The JAK3 inhibitors WHI-P131/JANEX-1 (4-(4'-Hydroxyphenyl)amino-6,7-dimethoxyquinazoline, 156μM) and WHI-P154 (4-[(3'-Bromo-4'-hydroxyphenyl)amino]-6,7-dimethoxyquinazoline, 11.2μM) did not significantly modify annexin V binding or forward scatter. Glucose depletion increased annexin V binding, an effect significantly blunted in jak3(-/-) erythrocytes and in the presence of the JAK3 inhibitors. The observations disclose a completely novel role of Janus kinase 3, i.e. the triggering of cell membrane scrambling in energy depleted erythrocytes.

Mechanistically probing lipid-siRNA nanoparticle-associated toxicities identifies Jak inhibitors effective in mitigating multifaceted toxic responses

A major hurdle for harnessing small interfering RNA (siRNA) for therapeutic application is an effective and safe delivery of siRNA to target tissues and cells via systemic administration. While lipid nanoparticles (LNPs) composed of a cationic lipid, poly-(ethylene glycol) lipid and cholesterol, are effective in delivering siRNA to hepatocytes via systemic administration, they may induce multi-faceted toxicities in a dose-dependent manner, independently of target silencing. To understand the underlying mechanism of toxicities, pharmacological probes including anti-inflammation drugs and specific inhibitors blocking different pathways of innate immunity were evaluated for their abilities to mitigate LNP-siRNA-induced toxicities in rodents. Three categories of rescue effects were observed: (i) pretreatment with a Janus kinase (Jak) inhibitor or dexamethasone abrogated LNP-siRNA-mediated lethality and toxicities including cytokine induction, organ impairments, thrombocytopenia and coagulopathy without affecting siRNA-mediated gene silencing; (ii) inhibitors of PI3K, mammalian target of rapamycin (mTOR), p38 and IκB kinase (IKK)1/2 exhibited a partial alleviative effect; (iii) FK506 and etoricoxib displayed no protection. Furthermore, knockout of Jak3, tumor necrosis factor receptors (Tnfr)p55/p75, interleukin 6 (IL-6) or interferon (IFN)-γ alone was insufficient to alleviate LNP-siRNA-associated toxicities in mice. These indicate that activation of innate immune response is a primary trigger of systemic toxicities and that multiple innate immune pathways and cytokines can mediate toxic responses. Jak inhibitors are effective in mitigating LNP-siRNA-induced toxicities.

Research on HIV/Toxoplasma gondii co-infection and cytokine levels among intravenous drug users

HIV and T. gondii infection markers were measured among 383 Intravenous Drug Users (IDU). And cytokine concentrations (IL-4, IL-6, IL-10, IL-12, IFN-gamma and TNF-alpha) were determined. The results showed IDU with HIV infection or HIV/T. gondii co-infection could disturb Th regulatory mechanism.

Ablation of tumor progression locus 2 promotes a type 2 Th cell response in Ovalbumin-immunized mice

The protein kinase encoded by the Tpl2 proto-oncogene regulates ERK activation and cytokine gene expression in macrophages in response to LPS and TNF-alpha. In this study we show that OVA-immunized Tpl2(-/-) mice express high levels of IgE and develop more severe bronchoalveolar eosinophilic inflammation than Tpl2(+/+) controls, when challenged with OVA intranasally. Bronchoalveolar exudates and supernatants of OVA-stimulated splenocytes from immunized Tpl2(-/-) mice express elevated levels of IL-4 and IL-5, suggesting that Tpl2 ablation promotes the Th2 polarization of the T cell response. Anti-CD3 stimulation of CD4(+) T cells of wild-type and Tpl2 knockout mice revealed that Tpl2 ablation gives rise to a cell autonomous T cell defect that is primarily responsible for the Th2 polarization of the T cell response to Ag. This observation was further supported by experiments addressing the expression of Th1 and Th2 cytokines in OVA-stimulated mixed cultures of CD4(+) T cells from Tpl2(+/+)/OT2 or Tpl2(-/-)/OT2 mice and dendritic cells from Tpl2(+/+) or Tpl2(-/-) mice. Further studies revealed that Th1 cells express significantly higher levels of Tpl2 than Th2 cells. As a result, Tpl2(-/-) Th1 cells exhibit a stronger defect in ERK activation by anti-CD3 than Th2 cells and express low levels of T-bet. Given that the development of Th1 and Th2 cells depends on positive feedback signals from the T cells, themselves, the functional defect of the Tpl2(-/-) Th1 cells provides a mechanistic explanation for the T cell autonomous Th2 polarization in Tpl2(-/-) mice.

Jak3 is involved in dendritic cell maturation and CCR7-dependent migration

Background

CCR7-mediated signalling is important for dendritic cell maturation and homing to the lymph nodes. We have previously demonstrated that Jak3 participates in the signalling pathway of CCR7 in T lymphocytes.

Methodology and Principal Findings

Here, we used Jak3^−/− mice to analyze the role of Jak3 in CCR7-mediated dendritic cells migration and function. First, we found no differences in the generation of DCs from Jak3^−/− bone marrow progenitors, when compared to wild type cells. However, phenotypic analysis of the bone marrow derived DCs obtained from Jak3^−/− mice showed reduced expression of co-stimulatory molecules compared to wild type (Jak3^+/+). In addition, when we analyzed the migration of Jak3^−/− and Jak3^+/+ mature DCs in response to CCL19 and CCL21 chemokines, we found that the absence of Jak3 results in impaired chemotactic responses both in vitro and in vivo. Moreover, lymphocyte proliferation and contact hypersensitivity experiments showed that DC-mediated T lymphocyte activation is reduced in the absence of Jak3.

Conclusion/Significance

Altogether, our data provide strong evidence that Jak3 is important for DC maturation, migration and function, through a CCR7-mediated signalling pathway.

Jak inhibitor ; possibility and mechanism as a new disease modifying anti-rheumatic drug

Treatment of rheumatoid arthritis (RA) has developed dramatically by the appearance of biologics. However the development of a new anti-rheumatic drug is necessary because of its issue on route of administration and expense. Recently, inhibitors targeting tyrosine kinase known as Janus kinase (Jak) has shown prominent effect on RA. Jak family is comprised by Jak1, Jak2, Jak3 and Tyk2 which is necessary for signal transduction for inflammatory cytokines. INCB18424 targeting Jak1/2 and CP690,550 targeting Jak3 has been developed and is now on phase II clinical study for RA. Results from those clinical studies have proven that these inhibitors can be effective as biologics with few side effects. However, it has been reported that inhibitors are less specific than it has been expect and that non-specificity can be important for its effect. Therefore, we think that the mechanism of inhibitors cannot be explained by its inhibition of a single kinase. Herein, we describe IL-10 overproduction by Jak3 and Stat6 deficient dendritic cell. We speculate that this is one possible mechanism of action for CP690,550 although as for its non-specificity we need further investigation to predict not only its effect but also its side effect in a long term administration.

Targeting innate immunity protein kinase signalling in inflammation

Inflammation is an evolutionarily conserved host reaction that is initiated in response to trauma, tissue damage and infection. It leads to changes in tissue homeostasis and blood flow, immune-cell activation and migration, and secretion of cytokines and mediators in a spatio-temporally coordinated manner. Progress in understanding of the mechanisms of the inflammatory response has identified various protein kinases that act as essential signalling components and therefore represent potential therapeutic targets. This article summarizes advances in the identification and validation of such targets, and discusses key issues for the development of small-molecule kinase inhibitors as a new generation of oral anti-inflammatory drugs, including feedback loops, inhibitor specificity and combination therapy.

Janus kinases in immune cell signaling

The Janus family kinases (Jaks), Jak1, Jak2, Jak3, and Tyk2, form one subgroup of the non-receptor protein tyrosine kinases. They are involved in cell growth, survival, development, and differentiation of a variety of cells but are critically important for immune cells and hematopoietic cells. Data from experimental mice and clinical observations have unraveled multiple signaling events mediated by Jaks in innate and adaptive immunity. Deficiency of Jak3 or Tyk2 results in defined clinical disorders, which are also evident in mouse models. A striking phenotype associated with inactivating Jak3 mutations is severe combined immunodeficiency syndrome, whereas mutation of Tyk2 results in another primary immunodeficiency termed autosomal recessive hyperimmunoglobulin E syndrome. By contrast, complete deletion of Jak1 or Jak2 in the mouse are not compatible with life and, unsurprisingly, do not have counterparts in human disease. However, activating mutations of each of the Jaks are found in association with malignant transformation, the most common being gain-of-function mutations of Jak2 in polycythemia vera and other myeloproliferative disorders. Our existing knowledge on Jak signaling pathways and fundamental work on their biochemical structure and intracellular interactions allow us to develop new strategies for controlling autoimmune diseases or malignancies by developing selective Jak inhibitors, which are now coming into clinical use. Despite the fact that Jaks were discovered only a little more than a decade ago, at the time of writing there are 20 clinical trials underway testing the safety and efficacy of Jak inhibitors.

Proinflammatory tachykinins that signal through the neurokinin 1 receptor promote survival of dendritic cells and potent cellular immunity

Dendritic cells (DCs) are the preferred targets for immunotherapy protocols focused on stimulation of cellular immune responses. However, regardless of initial promising results, ex vivo generated DCs do not always promote immune-stimulatory responses. The outcome of DC-dependent immunity is regulated by proinflammatory cytokines and neuropeptides. Proinflammatory neuropeptides of the tachykinin family, including substance P (SP) and hemokinin-1 (HK-1), bind the neurokinin 1 receptor (NK1R) and promote stimulatory immune responses. Nevertheless, the ability of pro-inflammatory tachykinins to affect the immune functions of DCs remains elusive. In the present work, we demonstrate that mouse bone marrow-derived DCs (BMDCs) generated in the presence of granulocyte macrophage-colony stimulating factor (GM-CSF) and interleukin-4 (IL-4), express functional NK1R. Signaling via NK1R with SP, HK-1, or the synthetic agonist [Sar(9)Met(O(2))(11)]-SP rescues DCs from apoptosis induced by deprivation of GM-CSF and IL-4. Mechanistic analysis demonstrates that NK1R agonistic binding promotes DC survival via PI3K-Akt signaling cascade. In adoptive transfer experiments, NK1R-signaled BMDCs loaded with Ag exhibit increased longevity in draining lymph nodes, resulting in enhanced and prolonged effector cellular immunity. Our results contribute to the understanding of the interactions between the immune and nervous systems that control DC function and present a novel approach for ex vivo-generation of potent immune-stimulatory DCs.

Novel immunosuppression: R348, a JAK3- and Syk-inhibitor attenuates acute cardiac allograft rejection

BACKGROUND

Janus kinase (JAK)3 is crucial for signal transduction downstream of various cytokine receptors in immune cells. This is the first report on the novel JAK3 inhibitor R348.

METHODS

(1) Detailed pharmacokinetic data were obtained in rats; (2) multiple in vitro enzyme inhibition assays were performed to characterize the drug; (3) prevention of acute rejection was investigated in animals treated with different doses of R348 or rapamycin for 5 days; and (4) cardiac allograft survival after a 10-day treatment period was studied for various regimens of R348, tacrolimus, or rapamycin; combination indices were calculated to evaluate drug interactions.

RESULTS

(1) Plasma levels of R348's active metabolite R333 sustained high for 8 hr or more, depending on the dose. (2) In vitro enzyme assays showed potent inhibition of JAK3- and Syk-dependent pathways. (3) R348 40 mg/kg preserved graft function, significantly reduced graft infiltration, and decreased histologic ISHLT rejection scores on postoperative day 5. Results were similar to those of rapamycin 3 mg/kg. Likewise, both drugs significantly reduced the cellular Th1 and Th2 immune responses, as determined by enzyme-linked immunosorbent assays. Intragraft inflammatory cytokine upregulation was similarly suppressed by R348 and rapamycin. R348 10 mg/kg was subtherapeutic. (4) Allograft survival was similar for R348 20 and 40 mg/kg, which was comparable with therapeutically dosed tacrolimus or rapamycin. In combination regimens, R348 demonstrated highly beneficial synergistic interactions with tacrolimus.

CONCLUSIONS

R348 is a promising novel JAK3/Syk-inhibitor with favorable pharmacokinetics and biological activity. It effectively diminishes acute cardiac allograft rejection and is suitable for combination regimens with tacrolimus.

The TNF receptor and Ig superfamily members form an integrated signaling circuit controlling dendritic cell homeostasis

Dendritic cells (DC) constitute the most potent antigen presenting cells of the immune system, playing a key role bridging innate and adaptive immune responses. Specialized DC subsets differ depending on their origin, tissue location and the influence of trophic factors, the latter remain to be fully understood. Myeloid-associated lymphotoxin-beta receptor (LTbetaR) signaling is required for the local proliferation of lymphoid tissue DC. This review focuses on the LTbetaR signaling cascade as a crucial positive trophic signal in the homeostasis of DC subsets. The noncanonical coreceptor pathway comprised of the immunoglobulin (Ig) superfamily member, B and T lymphocyte attenuator (BTLA) and TNFR superfamily member, herpesvirus entry mediator (HVEM) counter regulates the trophic signaling by LTbetaR. Together both pathways form an integrated signaling circuit achieving homeostasis of DC subsets.

The inhibitory HVEM-BTLA pathway counter regulates lymphotoxin receptor signaling to achieve homeostasis of dendritic cells

Proliferation of dendritic cells (DC) in the spleen is regulated by positive growth signals through the lymphotoxin (LT)-beta receptor; however, the countering inhibitory signals that achieve homeostatic control are unresolved. Mice deficient in LTalpha, LTbeta, LTbetaR, and the NFkappaB inducing kinase show a specific loss of CD8- DC subsets. In contrast, the CD8alpha- DC subsets were overpopulated in mice deficient in the herpesvirus entry mediator (HVEM) or B and T lymphocyte attenuator (BTLA). HVEM- and BTLA-deficient DC subsets displayed a specific growth advantage in repopulating the spleen in competitive replacement bone marrow chimeric mice. Expression of HVEM and BTLA were required in DC and in the surrounding microenvironment, although DC expression of LTbetaR was necessary to maintain homeostasis. Moreover, enforced activation of the LTbetaR with an agonist Ab drove expansion of CD8alpha- DC subsets, overriding regulation by the HVEM-BTLA pathway. These results indicate the HVEM-BTLA pathway provides an inhibitory checkpoint for DC homeostasis in lymphoid tissue. Together, the LTbetaR and HVEM-BTLA pathways form an integrated signaling network regulating DC homeostasis.

Transcription factors in the control of dendritic cell life cycle

Dendritic cells (DCs) are potent antigen-presenting cells that guard all parts of the body. They have the unique ability to prime T cells and generate primary immune responses. Their journey beginning with the development from precursor cells and ending with their death is controlled by a group of transcription factors. Some of the transcription factors like PU.1 are involved in more than one stage of DC life. Other transcription factors including Ikaros and JAK3 are involved in the development of more than one cell type. For a long time, the cellular and molecular mechanisms underlying the development, differentiation, maturation, and other stages of DC life were not well understood. However, in recent years novel information has been published by many researchers to better understand the molecular mechanisms of the development and function of DCs in immunological diseases such as asthma, cancer, autoimmunity, and transplantation. This review will discuss the various transcription factors and signaling pathways involved in each stage of the life cycle of DCs.

Kaempferol Inhibits IL-4-Induced STAT6 Activation by Specifically Targeting JAK3

IL-4 is involved in several human diseases including allergies, autoimmunity, and cancer. Its effects are mainly mediated through the transcription factor STAT6. Therefore, investigation of compounds that regulate STAT6 activation is of great interest for these diseases. Natural polyphenols are compounds reported to have therapeutic properties in diseases involving IL-4 and STAT6. The aim of this study was to investigate the effect of these compounds in the activation of this transcription factor. We found that in hemopoietic cells from human and mouse origin, some flavonoids were able to inhibit the activation of STAT6 by IL-4. To identify molecular mechanisms, we focused on kaempferol, the compound that showed the greatest inhibitory effect with the lowest cell toxicity. Treatment of cells with kaempferol did not affect activation of Src kinase by IL-4 but did prevent the phosphorylation of JAK1 and JAK3. Further enzymatic analysis demonstrated that kaempferol blocked the in vitro phosphorylation activity of JAK3 without affecting JAK1, suggesting that it specifically targeted JAK3 activity. Accordingly, kaempferol had no effect on STAT6 activation in nonhemopoietic cell lines lacking JAK3, supporting its selective inhibition of IL-4 responses through type I receptors expressing JAK3 but not type II lacking this kinase. The inhibitory effect of kaempferol was also observed in IL-2 but not IL-3-mediated responses and correlated with the inhibition of MLC proliferation. These findings reveal the potential use of kaempferol as a tool for selectively controlling cell responses to IL-4 and, in general, JAK3-dependent responses.

Role of IL-21 in immune-regulation and tumor immunotherapy

IL-21, the most recently discovered member of the IL-2 cytokine family, is an attractive subject for research due to its involvement in experimental models of autoimmunity, its ability to down-regulate IgE production, and its anti-tumor properties. Its interest for cancer immunotherapy stems from its physiological immune-enhancing functions. These include regulation of T, B and NK cell proliferation, survival, differentiation, and effector functions. IL-21's functional activities partially overlap those of IL-2. Both cytokines display similar structural features and use the common gamma-chain receptor and its downstream signaling pathways. Besides its activities on normal lymphoid cells, IL-21 is an in vitro growth factor for myeloma and acute-T cell leukemia cells, whereas it induces the apoptosis of B-CLL (chronic lymphocytic leukemia) cells. These findings indicate that the IL-21/IL-21R system exerts opposite functions in different lymphoid neoplasias, and suggest its employment in B-CLL therapy. Since IL-2, but not IL-21, is specifically required for the development of regulatory T (Treg) cell immune-suppressive functions, IL-21 may be a new tool for cancer immunotherapy. It is, in fact, a powerful anti-tumor agent in a variety of murine experimental tumor models through its activation of specific or innate immune responses against neoplastic cells. The preliminary data from phase-I clinical studies suggest that the use of IL-21 is feasible and may result in immune-enhancing effects.

Impaired cytokine production and suppressed lymphocyte proliferation activity in HCV-infected cocaine and heroin ("speedball") users

HCV-infected "speedball" users (n = 30) were selected from an original cohort of 400 intravenous drug users for cytokine analysis. Cytokine concentrations (TNF-alpha, IL-1beta, IL-6, IFN-gamma, IL-2, IL-4, IL-10 and IL-12) were determined in plasma and peripheral blood mononuclear cells (PBMC) cultures derived ex vivo from these patients. In addition, lymphocyte proliferation was measured in 49 HCV-positive "speedball" users. TNF-alpha, IL-6, IFN-gamma, IL-2, IL-4, IL-10, IL-12 cytokines and not IL-1beta were significantly increased in plasma from HCV-positive "speedball" users compared with healthy controls. Except for IL-10, all other cytokines measured were augmented in phytohemagglutinin-stimulated PBMC cultures from HCV-positive "speedball" users. Likewise, overproduction of cytokines TNF-alpha, IL-1beta, IL-6 and IFN-gamma, was consistently detected when PBMC cultures from HCV-positive "speedball" users were stimulated with a biological response modifier. However, HCV-infected "speedball" users showed significant reduction in lymphoproliferative activity. Compared with healthy subjects, there was a consistent overproduction of both TH1 and TH2 type cytokines in the plasma and PBMC's of HCV-infected "speedball" users. Furthermore, there was a persistent reduction of lymphoproliferative activity in this group. These immunologic abnormalities, coupled with the range of response between the two TH-types in HCV-infected "speedball" users, suggest impairment in the regulatory mechanism of the TH1-TH2 system.

Cytohesin binder and regulator (cybr) is not essential for T- and dendritic-cell activation and differentiation

Cybr (also known as Cytip, CASP, and PSCDBP) is an interleukin-12-induced gene expressed exclusively in hematopoietic cells and tissues that associates with Arf guanine nucleotide exchange factors known as cytohesins. Cybr levels are dynamically regulated during T-cell development in the thymus and upon activation of peripheral T cells. In addition, Cybr is induced in activated dendritic cells and has been reported to regulate dendritic cell (DC)-T-cell adhesion. Here we report the generation and characterization of Cybr-deficient mice. Despite the selective expression in hematopoietic cells, there was no intrinsic defect in T- or B-cell development or function in Cybr-deficient mice. The adoptive transfer of Cybr-deficient DCs showed that they migrated efficiently and stimulated proliferation and cytokine production by T cells in vivo. However, competitive stem cell repopulation experiments showed a defect in the abilities of Cybr-deficient T cells to develop in the presence of wild-type precursors. These data suggest that Cybr is not absolutely required for hematopoietic cell development or function, but stem cells lacking Cybr are at a developmental disadvantage compared to wild-type cells. Collectively, these data demonstrate that despite its selective expression in hematopoietic cells, the role of Cybr is limited or largely redundant. Previous in vitro studies using overexpression or short interfering RNA inhibition of the levels of Cybr protein appear to have overestimated its immunological role.

Janus tyrosine kinases and signal transducers and activators of transcription regulate critical functions of T cells in allograft rejection and transplantation tolerance

Full activation of T cells requires three sequential signals. Engagement by antigen presenting cells (APC) delivers signals 1/2, whereas signal 3 is delivered by multiple cytokines to regulate the immune homeostasis by influencing proliferation, differentiation, and survival/death. Signaling by cytokines acting through their receptors is delivered by two major molecular families, namely Janus tyrosine kinases (Jaks) and signal transducers and activators of transcription (Stats). Findings obtained from mice genetically deficient in Jaks and Stats suggest that these molecules may serve as therapeutic targets to prevent allograft rejection, induce transplantation tolerance, and inhibit autoimmune disease and lymphoid-derived tumors. This review describes the role of Jak tyrosine kinases and Stat transcription factors and their putative function in regulating T and B cell activity.