IL-23 past, present, and future: a roadmap to advancing IL-23 science and therapy.

Interleukin (IL)-23, an IL-12 cytokine family member, is a hierarchically dominant regulatory cytokine in a cluster of immune-mediated inflammatory diseases (IMIDs), including psoriasis, psoriatic arthritis, and inflammatory bowel disease. We review IL-23 biology, IL-23 signaling in IMIDs, and the effect of IL-23 inhibition in treating these diseases. We propose studies to advance IL-23 biology and unravel differences in response to anti-IL-23 therapy. Experimental evidence generated from these investigations could establish a novel molecular ontology centered around IL-23-driven diseases, improve upon current approaches to treating IMIDs with IL-23 inhibition, and ultimately facilitate optimal identification of patients and, thereby, outcomes.

Guselkumab More Effectively Neutralizes Psoriasis-Associated Histologic, Transcriptomic, and Clinical Measures than Ustekinumab.

Given the key role of the IL-23/Th17 axis in the pathogenesis of moderate-to-severe plaque psoriasis, several specific inhibitors of the p19 subunit of IL-23 have been approved to treat this chronic inflammatory disease. Clinical data indicate that guselkumab, one such selective IL-23 inhibitor, achieves greater clinical efficacy compared with ustekinumab, which inhibits both IL-12 and IL-23 via binding their shared p40 subunit. To understand mechanisms underlying the enhanced efficacy observed with the p19 subunit of IL-23-specific inhibition, we explored cellular and molecular changes in skin of psoriasis patients treated with ustekinumab or guselkumab and in ustekinumab inadequate responders (Investigator's Global Assessment of psoriasis score ≥ 2) subsequently treated with guselkumab (ustekinumab→guselkumab). Skin biopsies were collected pretreatment and posttreatment to assess histologic changes and molecular responses in ustekinumab- and guselkumab-treated patients. Serum cytokines and skin transcriptomics from the subset of ustekinumab→guselkumab-treated patients were also analyzed to characterize differential treatment effects. Ustekinumab and guselkumab demonstrated differential effects on secretion of pathogenic Th17-related cytokines induced by IL-23 in in vitro assays, which suggest guselkumab is a more potent therapeutic agent. Consistent with these findings, guselkumab elicited a significantly greater reduction in cellular and molecular psoriasis-related disease indicators than ustekinumab. In ustekinumab→guselkumab patients, suppression of serum IL-17A and IL-17F levels and neutralization of molecular scar and psoriasis-related gene markers in skin were significantly greater compared with patients continuing ustekinumab. This comparative study demonstrates that guselkumab inhibits psoriasis-associated pathology, suppresses Th17-related serum cytokines, and normalizes the psoriasis skin gene expression profile more effectively than ustekinumab.

Combined Blockade of TNF-α and IL-17A Alleviates Progression of Collagen-Induced Arthritis without Causing Serious Infections in Mice.

The cytokines TNF-α and IL-17A are elevated in a variety of autoimmune diseases, including rheumatoid arthritis. Both cytokines are targets of several biologic drugs used in the clinic, but unfortunately many patients are refractory to these therapies. IL-17A and TNF-α are known to mediate signaling synergistically to drive expression of inflammatory genes. Hence, combined blockade of TNF-α and IL-17A represents an attractive treatment strategy in autoimmune settings where monotherapy is not fully effective. However, a major concern with this approach is the potential predisposition to opportunistic infections that might outweigh any clinical benefits. Accordingly, we examined the impact of individual versus combined neutralization of TNF-α and IL-17A in a mouse model of rheumatoid arthritis (collagen-induced arthritis) and the concomitant susceptibility to infections that are likely to manifest as side effects of blocking these cytokines (oral candidiasis or tuberculosis). Our findings indicate that combined neutralization of TNF-α and IL-17A was considerably more effective than monotherapy in improving collagen-induced arthritis disease even when administered at a minimally efficacious dose. Encouragingly, however, dual cytokine blockade did not cooperatively impair antimicrobial host defenses, as mice given combined IL-17A and TNF-α neutralization displayed infectious profiles and humoral responses comparable to mice given high doses of individual anti-TNF-α or anti-IL-17A mAbs. These data support the idea that combined neutralization of TNF-α and IL-17A for refractory autoimmunity is likely to be associated with acceptable and manageable risks of opportunistic infections associated with these cytokines.

IL-27 Limits Type 2 Immunopathology Following Parainfluenza Virus Infection.

Respiratory paramyxoviruses are important causes of morbidity and mortality, particularly of infants and the elderly. In humans, a T helper (Th)2-biased immune response to these infections is associated with increased disease severity; however, little is known about the endogenous regulators of these responses that may be manipulated to ameliorate pathology. IL-27, a cytokine that regulates Th2 responses, is produced in the lungs during parainfluenza infection, but its role in disease pathogenesis is unknown. To determine whether IL-27 limits the development of pathogenic Th2 responses during paramyxovirus infection, IL-27-deficient or control mice were infected with the murine parainfluenza virus Sendai virus (SeV). Infected IL-27-deficient mice experienced increased weight loss, more severe lung lesions, and decreased survival compared to controls. IL-27 deficiency led to increased pulmonary eosinophils, alternatively activated macrophages (AAMs), and the emergence of Th2 responses. In control mice, IL-27 induced a population of IFN-γ+/IL-10+ CD4+ T cells that was replaced by IFN-γ+/IL-17+ and IFN-γ+/IL-13+ CD4+ T cells in IL-27-deficient mice. CD4+ T cell depletion in IL-27-deficient mice attenuated weight loss and decreased AAMs. Elimination of STAT6 signaling in IL-27-deficient mice reduced Th2 responses and decreased disease severity. These data indicate that endogenous IL-27 limits pathology during parainfluenza virus infection by regulating the quality of CD4+ T cell responses and therefore may have therapeutic potential in paramyxovirus infections.

Molecular Mechanisms of Airway Hyperresponsiveness in a Murine Model of Steroid-Resistant Airway Inflammation.

IL-13 and IL-17A, produced mainly by Th2 and Th17 cells, respectively, have an influential role in asthma pathogenesis. We examined the role of IL-13 and IL-17A in mediating airway hyperresponsiveness (AHR), lung inflammation, and mucus metaplasia in a dual Th2/Th17 model of asthma. IL-13 and/or IL-17A were neutralized using mAbs. Th2/Th17 adoptive transfer induced a mixed asthma phenotype characterized by elevated eosinophilia and neutrophilia, tissue inflammation, mucus metaplasia, and AHR that were partially reversible with steroid treatment. Pulmonary inflammation and quasi-static lung compliance were largely unaffected by neutralization of IL-13 and/or IL-17A. However, neutralization of IL-13 alone or in combination with IL-17A significantly attenuated AHR and mucus metaplasia. Further, STAT6 activation was attenuated following IL-13 and IL-13/IL-17A Ab treatment. We next assessed the role of STAT6 in Th2/Th17-mediated allergic airway disease using STAT6(-/-) mice. STAT6(-/-) mice adoptively transferred with Th2/Th17 cells had decreased AHR compared with controls. These data suggest that IL-13 drives AHR and mucus metaplasia in a STAT6-dependent manner, without directly contributing to airway or tissue inflammation. IL-17A independently contributes to AHR, but it only partially mediates inflammation and mucus metaplasia in a mixed Th2/Th17 model of steroid-resistant asthma.

The cytokines interleukin 27 and interferon-γ promote distinct Treg cell populations required to limit infection-induced pathology.

Interferon-γ (IFN-γ) promotes a population of T-bet(+) CXCR3(+) regulatory T (Treg) cells that limit T helper 1 (Th1) cell-mediated pathology. Our studies demonstrate that interleukin-27 (IL-27) also promoted expression of T-bet and CXCR3 in Treg cells. During infection with Toxoplasma gondii, a similar population emerged that limited T cell responses and was dependent on IFN-γ in the periphery but on IL-27 at mucosal sites. Transfer of Treg cells ameliorated the infection-induced pathology observed in Il27(-/-) mice, and this was dependent on their ability to produce IL-10. Microarray analysis revealed that Treg cells exposed to either IFN-γ or IL-27 have distinct transcriptional profiles. Thus, IFN-γ and IL-27 have different roles in Treg cell biology and IL-27 is a key cytokine that promotes the development of Treg cells specialized to control Th1 cell-mediated immunity at local sites of inflammation.

Targeting the Th17 pathway in psoriasis.

In recent years, the classic paradigm of Th1/Th2 CD4(+) T cell-mediated immunity has evolved to include the IL-17A-producing Th17 subset, a distinct proinflammatory CD4(+) T cell lineage. Accumulating evidence suggests that IL-17A and the Th17 pathway may play an important role in the pathology of psoriasis and in other immune-mediated inflammatory diseases. This review summarizes the preclinical and clinical evidence implicating Th17 cells in psoriasis and the therapeutic approaches, approved or under investigation, to target this pathway in psoriasis.

Distinct roles of IL-23 and IL-17 in the development of psoriasis-like lesions in a mouse model.

Psoriasis is an inflammatory disease with dynamic interactions between the immune system and the skin. The IL-23/Th17 axis plays an important role in the pathogenesis of psoriasis, although the exact contributions of IL-23 and IL-17 in vivo remain unclear. K5.Stat3C transgenic mice constitutively express activated Stat3 within keratinocytes, and these animals develop skin lesions with histological and cytokine profiles similar to those of human plaque psoriasis. In this study, we characterized the effects of anti-mouse IL-17A, anti-mouse IL-12/23p40, and anti-mouse IL-23p19 Abs on the development of psoriasis-like lesions in K5.Stat3C transgenic mice. Treatment with anti-IL-12/23p40 or anti-IL-23p19 Abs greatly inhibited 12-O-tetradecanoylphorbol-13-acetate-induced epidermal hyperplasia in the ears of K5.Stat3C mice, whereas the inhibitory effect of an anti-IL-17A Ab was relatively less prominent. Treatment with anti-IL-12/23p40 or anti-IL-23p19 Abs markedly lowered transcript levels of Th17 cytokines (e.g., IL-17 and IL-22), ß-defensins, and S100A family members in skin lesions. However, anti-IL-17A Ab treatment did not affect mRNA levels of Th17 cytokines. Crossing IL-17A-deficient mice with K5.Stat3C mice resulted in partial attenuation of 12-O-tetradecanoylphorbol-13-acetate-induced lesions, which were further attenuated by anti-IL-12/23p40 Ab treatment. FACS analysis of skin-draining lymph node cells from mice that were intradermally injected with IL-23 revealed an increase in both IL-22-producing T cells and NK-22 cells. Taken together, this system provides a useful mouse model for psoriasis and demonstrates distinct roles for IL-23 and IL-17.

CD4(+) lymphoid tissue-inducer cells promote innate immunity in the gut.

Fetal CD4(+) lymphoid tissue inducer (LTi) cells play a critical role in the development of lymphoid tissues. Recent studies identified that LTi cells persist in adults and are related to a heterogeneous population of innate lymphoid cells that have been implicated in inflammatory responses. However, whether LTi cells contribute to protective immunity remains poorly defined. We demonstrate that after infection with Citrobacter rodentium, CD4(+) LTi cells were a dominant source of interleukin-22 (IL-22) early during infection. Infection-induced CD4(+) LTi cell responses were IL-23 dependent, and ablation of IL-23 impaired innate immunity. Further, depletion of CD4(+) LTi cells abrogated infection-induced expression of IL-22 and antimicrobial peptides, resulting in exacerbated host mortality. LTi cells were also found to be essential for host protective immunity in lymphocyte-replete hosts. Collectively these data demonstrate that adult CD4(+) LTi cells are a critical source of IL-22 and identify a previously unrecognized function for CD4(+) LTi cells in promoting innate immunity in the intestine.

Expression, refolding and purification of a human interleukin-17A variant.

A human interleukin-17A (IL-17A) variant was overexpressed in Escherichia coli BL21 (DE3) under the control of a T(7) promoter. The resulting insoluble inclusion bodies were isolated and solubilized by homogenization with 6 M guanidine HCl. The denatured recombinant human IL-17A variant was refolded in 20 mM Tris-HCl, pH 9.0, 500 mM arginine, 500 mM guanidine HCl, 15% glycerol, 1 mM cystamine, and 5 mM cysteine at 2-8°C for 40 h. The refolded IL-17A variant was subsequently purified using a combination of cation-exchange, reversed-phase and fluoroapatite chromatography. The final purified product was a monodisperse and crystallizable homodimer with a molecular weight of 30,348.3 Da. The protein was active in both receptor binding competition assay and IL-17A-dependent biological activity assay using human dermal fibroblasts.

Proinflammatory/profibrotic effects of interleukin-17A on human proximal tubule epithelium.

BACKGROUND/AIMS: Interleukin-17A (IL-17A) is a T cell-derived inflammatory cytokine that is upregulated during renal allograft rejection. The present study sought to further describe the IL-17A-mediated proinflammatory/profibrotic activity of proximal tubule epithelium that may contribute to allograft rejection. METHODS: Immortalized (HK-2) and primary (HRPTEpiC) human proximal tubule epithelial cells were utilized for this study. Profibrotic gene alterations were examined by real-time quantitative PCR. Inflammatory mediator secretion was examined by multiplex bead-based detection of secreted proteins. Immunofluorescence microscopy and immunoblotting were utilized to examine alterations in junctional protein expression and cell morphology. RESULTS: In HK-2 cells IL-17A significantly downregulated the expression of the proepithelial gene CDH1 (E-cadherin) while the proinflammatory/profibrotic genes CTGF, CD44 and TGFBR1 were significantly increased. IL-17A also increased the secretion of fractalkine, G-CSF, GM-CSF, VEGF, IL-6 and IL-8. In HRPTEpiC 100 ng/ml IL-17A upregulated the proinflammatory/profibrotic genes ACTA2, CCL2, CHMP1A, CTGF, FN1, IL6, FSP1, SMAD1, SMAD5, TGFB1 and TGFBR2 while treatment with a reduced concentration of IL-17A (0.1 ng/ml) decreased SMAD5, TGFB1 and PDGFRB expression. Changes in ZO-1 and E-cadherin protein expression and cell morphology were examined following IL-17A treatment as indicators of epithelial-to-mesenchymal transition. IL-17A decreased ZO-1 expression in HK-2 and HRPTEpiC; however, E-cadherin was only reduced in HK-2 cells. Neither HK-2 nor HRPTEpiC assumed an elongated, fibroblast-like morphology following IL-17A treatment. CONCLUSIONS: IL-17A directly mediates proximal tubule epithelial cell proinflammatory/profibrotic activity as demonstrated by the alteration in genes associated with extracellular matrix remodeling and cell-cell interaction, and stimulation of inflammatory mediator and immune cell chemoattractant secretion. Additionally, IL-17A may have a negative impact on barrier integrity as indicated by ZO-1 downregulation.

Bile acids induce adhesion molecule expression in endothelial cells through activation of reactive oxygen species, NF-kappaB, and p38.

Bile acids are synthesized in the liver, stored in gallbladder, and secreted into the intestine to aid in the absorption of lipid-soluble nutrients. In addition, bile acids also actively participate in regulation of gene expression through their ability to act as ligands for the nuclear receptor farnesoid X receptor or by activating kinase signaling pathways. Under cholestatic conditions, elevated levels of bile acids in the liver induce hepatic inflammation, and because bile acid levels are also elevated in the circulation, they might also induce vascular inflammation. To test this hypothesis, primary human umbilical vein endothelial cells (HUVEC) and human aortic endothelial cells were treated with bile acids, and the expression of ICAM-1, VCAM-1, and E-selectin were monitored. The three major bile acids found in the circulation, chenodeoxycholic acid, deoxycholic acid, and lithocholic acid, all strongly induced both the mRNA and protein expression of ICAM-1 and VCAM-1. To delineate the mechanism, the experiments were conducted in the presence of various kinase inhibitors. The results demonstrate that the bile acid-mediated induction of adhesion molecule expression occurs by stimulation of NF-kappaB and p38 MAPK signaling pathways through the elevation in reactive oxygen species. The bile acid-induced cell surface expression of ICAM-1 and VCAM-1 was sufficient to result in the increased adhesion of THP-1 monocytes to the HUVEC, suggesting that elevated levels of bile acids in the circulation may cause endothelium dysfunction and contribute to the initiation of early events associated with vascular lesion formation.

Suppression of experimental autoimmune encephalomyelitis using estrogen receptor-selective ligands.

Estrogens have been shown to modulate disease activity in experimental autoimmune encephalomyelitis (EAE), the mouse model for multiple sclerosis. Consistent with these findings, the severity of disease is reduced in pregnant women with multiple sclerosis when levels of estrogens are high. Estrogens bind to two known estrogen receptors (ER), ERalpha and ERbeta. The relative contribution of these receptors to estrogen-mediated suppression of EAE was explored using ER-selective ligands. The ER antagonist ICI 182 780 reversed the suppressive effects of 17beta-estradiol (E2), demonstrating that the protective effects of E2 on disease are dependent upon ER signaling. Treatment of SJL mice with the ERalpha-selective agonist proteolipid protein (PPT) prior to the induction of disease resulted in suppression of clinical symptoms of disease, whereas treatment with an ERbeta-selective agonist (WAY-202041) had no effect. Treatment of mice with PLP peptide 139-151 (PPT) was also associated with decreased immune responses associated with disease. Consistent with its lack of effect on disease, the ERbeta agonist had minimal effects on immune responses. The use of selective estrogen receptor modulators (SERMs) in this model was also explored, and we show that raloxifene and WAY-138923 were also effective in suppressing disease. These results demonstrate the beneficial effects of estrogen receptor ligands, in particular ERalpha-selective ligands, and may have implications in the development of therapeutic strategies for multiple sclerosis.

Differential estrogen receptor gene expression in human peripheral blood mononuclear cell populations.

Estrogens have been shown to modulate immune responses. Several studies have demonstrated the capacity of T cells, B cells, and monocytes to respond to estrogens and estrogen receptor (ER) expression in these cell types has been reported. However, little is known regarding the relative expression in these cells of ERalpha and the more recently identified ERbeta. In the present study, results of quantitative TaqMan RT-PCR analyses indicate that ERs are differentially expressed in PBMC subsets. CD4+ T cells express relatively high levels of ERalpha mRNA compared with ERbeta, whereas B cells express high levels of ERbeta mRNA but low levels of ERalpha. Peripheral blood CD8+ T cells and monocytes express low but comparable levels of both ERs. This quantitative analysis of ER expression in distinct PBMC subsets may provide a basis for dissecting the mechanisms of immune modulation by estrogens and identifying therapeutic targets for the treatment of inflammatory and immunologic disorders.

Protective effect of the immunosuppressant sirolimus against aortic atherosclerosis in apo E-deficient mice.

Atherosclerosis is a chronic inflammatory disease that develops in response to injury to the vessel wall, and is augmented by hypercholesterolemia. To further delineate the role of the immune system and local factors in this process, we assessed the effects of the immunosuppressant sirolimus (Rapamycin, RAPAMUNE, Wyeth, Collegeville, PA) on atherosclerosis in the apoE-deficient (apoE KO) mouse, a well-accepted model of cardiovascular disease. ApoE KO mice were fed a high fat diet and sirolimus was administered. After 12 weeks, atherosclerotic lesions and plasma lipoproteins were measured. The expression of cytokines associated with atherosclerosis was also examined. All groups demonstrated plasma total cholesterol (TC) >1100 mg/dL. Sirolimus treatment was associated with a 30% increase in LDL-cholesterol (LDLc) and a dose-dependent elevation in HDL-cholesterol (HDLc). Despite increased LDLc, aortic atherosclerosis was markedly reduced in all sirolimus-treated groups. Sirolimus treatment resulted in decreased expression of IL-12p40, IFN-gamma and IL-10 mRNA. In contrast, TGF-beta1 was elevated. Sirolimus significantly reduced atherosclerosis in apo E-KO mice; this effect is independent of, and obviates, elevated plasma TC and LDLc. Sirolimus might therefore be of benefit on atherosclerosis in patients undergoing therapy, independent of any impact on circulating lipids.