Suppressive and pro‐inflammatory roles for IL‐4 in the pathogenesis of experimental drug‐induced liver injury

The pathogenesis of immune‐mediated drug‐induced liver injury (DILI) following halogenated anesthetics, carbamazepine or alcohol has not been fully elucidated. Detecting cytochrome P450 2E1 (CYP2E1) IgG4 auto‐antibodies in anesthetic DILI patients suggests a role for IL‐4 in this hapten‐mediated process. We investigated IL‐4‐mediated mechanisms using our model of experimental DILI induced by immunizing BALB/c (WT) and IL‐4^?/? (KO) mice with S100 liver proteins covalently modified by a trifluoroacetyl chloride (TFA) hapten formed following halogenated anesthetic metabolism by CYP2E1. WT mice developed more hepatitis, TFA and S100 antibodies (p<0.01), as well as T‐cell proliferation to CYP2E1 and TFA (p<0.01) than KO mice. Additionally, WT CD4⁺ T cells adoptively transferred hepatitis to naïve Rag^?/? mice (p<0.01). Pro‐inflammatory cytokines were expectedly decreased in TFA hapten‐stimulated KO splenocyte supernatants (p<0.001); however, IL‐2 and IFN‐γ (p<0.05), as well as IL‐6 and IL‐10 (p<0.001) levels were elevated in CYP2E1‐stimulated KO splenocyte supernatants, suggesting dual IL‐4‐mediated pro‐inflammatory and regulatory responses. Anti‐IL‐10 administered to KO mice increased hepatitis, TFA and CYP2E1 antibodies in KO mice confirming a critical role for IL‐4. This is the first demonstration of dual roles for IL‐4 in the pathogenesis of immune‐mediated DILI by suppressing auto‐antigen‐induced regulatory responses while promoting hapten‐induced pro‐inflammatory responses.     

Novel therapeutic compound tuftsin–phosphorylcholine attenuates collagen‐induced arthritis

Treatment with helminthes and helminthes ova improved the clinical symptoms of several autoimmune diseases in patients and in animal models. Phosphorylcholine (PC) proved to be the immunomodulatory molecule. We aimed to decipher the tolerogenic potential of tuftsin–PC (TPC), a novel helminth‐based compound in collagen‐induced arthritis (CIA) a mouse model of rheumatoid arthritis (RA). CIA DBA/1 mice were treated with TPC subcutaneously (5 µg/0.1 ml) or orally (250 µg/0.1 ml), starting prior to disease induction. The control groups were treated with PBS. Collagen antibodies were tested by enzyme‐linked immunosorbent assay (ELISA), cytokine protein levels by ELISA kits and regulatory T (T_reg) and regulatory B (B_reg) cell phenotypes by fluorescence‐activated cell sorter (FACS). TPC‐treated mice had a significantly lower arthritis score of 1.5 in comparison with control mice 11.8 (P < 0.0001) in both subcutaneous and orally treated groups at day 31. Moreover, histology analysis demonstrated highly inflamed joints in control mice, whereas TPC‐treated mice maintained normal joint structure. Furthermore, TPC decreased the titres of circulating collagen II antibodies in mice sera (P < 0.0001), enhanced expression of IL‐10 (P < 0.0001) and inhibited production of tumour necrosis factor (TNF)‐α, interleukin (IL)?17 and IL‐1β (P < 0.0001). TPC significantly expanded the CD4⁺CD25⁺ forkhead box protein 3 (FoxP3⁺) T_reg cells and CD19⁺IL‐10⁺CD5^highCD1d^highT cell immunoglobulin mucin‐1 (TIM‐1⁺) B_reg cell phenotypes (P < 0.0001) in treated mice. Our data indicate that treatment with TPC attenuates CIA in mice demonstrated by low arthritic score and normal joints histology. TPC treatment reduced proinflammatory cytokines and increased anti‐inflammatory cytokine expression, as well as expansion of T_reg and B_reg cells. Our results may lead to a new approach for a natural therapy for early rheumatoid arthritis onset.     

Immunisation route‐dependent expression of IL‐4/IL‐13 can modulate HIV‐specific CD8+ CTL avidity

All HIV‐1 ‘systemic vaccine trials’ in humans have yielded poor outcomes. Thus, it is important to understand whether the route of delivery influences the quality of protective CTL immunity. Using heterologous poxvirus immunisation we have shown that systemically (i.m./i.m.) immunised CD8⁺ T cells generated higher levels of IL‐4/IL‐13 compared to mucosal delivery and expression also correlated with i.m./i.m. immunised mice eliciting CTL of lower avidity. Studies using IL‐4^?/? and IL‐13^?/? KO mice have shown that the capacity to express IFN‐γ, IL‐4 and/or IL‐13 by K^dGag_197–205‐specific CTL differed between these groups and was inversely correlated with CTL avidity (IL‐13^?/?>IL‐4^?/?>BALB/c), although no significant differences in the magnitude of CTL responses were observed between IL‐13^?/? and wild type mice. When IL‐13 was reconstituted in IL‐13^?/? splenocytes in vitro, their ability to bind tetramers also decreased significantly. Our data reveal that total absence of IL‐13 can greatly enhance CTL avidity. In contrast, extracellular IL‐4 appears to be important in maintaining long‐term Th1/Th2 balance in CTL, even though expression of IL‐4 by CTL markedly reduced avidity. STAT6^?/? mice also showed memory CTL of higher avidity. Furthermore, CCL5 expression in K^dGag_197–205‐specific CTL was also regulated by IL‐4/IL‐13.     

Galectin‐9 expands immunosuppressive macrophages to ameliorate T‐cell‐mediated lung inflammation

Galectin‐9 (Gal‐9) plays pivotal roles in the modulation of innate and adaptive immunity to suppress T‐cell‐mediated autoimmune models. However, it remains unclear if Gal‐9 plays a suppressive role for T‐cell function in non‐autoimmune disease models. We assessed the effects of Gal‐9 on experimental hypersensitivity pneumonitis induced by Trichosporon asahii. When Gal‐9 was given subcutaneously to C57BL/6 mice at the time of challenge with T. asahii, it significantly suppressed T. asahii‐induced lung inflammation, as the levels of IL‐1, IL‐6, IFN‐γ, and IL‐17 were significantly reduced in the BALF of Gal‐9‐treated mice. Moreover, co‐culture of anti‐CD3‐stimulated CD4 T cells with BALF cells harvested from Gal‐9‐treated mice on day 1 resulted in diminished CD4 T‐cell proliferation and decreased levels of IFN‐γ and IL‐17. CD11b⁺Ly‐6C^highF4/80⁺ BALF M? expanded by Gal‐9 were responsible for the suppression. We further found in vitro that Gal‐9, only in the presence of T. asahii, expands CD11b⁺Ly‐6C^highF4/80⁺ cells from BM cells, and the cells suppress T‐cell proliferation and IFN‐γ and IL‐17 production. The present results indicate that Gal‐9 expands immunosuppressive CD11b⁺Ly‐6C^high M? to ameliorate Th1/Th17 cell‐mediated hypersensitivity pneumonitis.     

The influence of bone marrow‐ and synovium‐derived mesenchymal stromal cells from osteoarthritis patients on regulatory T cells in co‐culture

There is increasing evidence that inflammation in the synovium plays a major role in the progression of osteoarthritis (OA). However, the immunogenic properties of mesenchymal stromal cells (MSCs), which are considered to regulate immunity in various diseases, remain largely unknown in OA. The purpose of this study was to determine the influence of MSCs from OA patients on regulatory T cells (T_regs) in an allogeneic co‐culture model. Bone marrow (BM) and synovial membrane (SM) were harvested from hip joints of OA patients and co‐cultured with lymphocytes enriched in CD4⁺CD25⁺CD127^– regulatory T cells (T_reg⁺LC) from healthy donors. T_reg proportions and MSC markers were assessed by flow cytometry. Cytokine levels were assessed after 2 and 5 days of co‐cultivation. Additionally, T_reg⁺LC cultures were analysed in the presence of interleukin (IL)‐6 and MSC‐supernatant complemented medium. B‐MSCs and S‐MSCs were able to retain the T_reg proportion compared to lymphocyte monocultures. T cell–MSC co‐cultures showed a significant increase of IL‐6 compared to MSC cultures. S‐MSCs produced higher amounts of IL‐6 compared to B‐MSCs, both in single and T cell co‐cultures. The effect of retaining the T_reg percentage could be reproduced partially by IL‐6 addition to the medium, but could only be observed fully when using MSC culture supernatants. Our data demonstrate that retaining the T_reg phenotype in MSC–T cell co‐cultures can be mediated by MSC derived from OA patients. IL‐6 plays an important role in mediating these processes. To our knowledge, this study is the first describing the interaction of MSCs from OA patients and T_regs in an allogeneic co‐culture model.     

Treatment of collagen‐induced arthritis by Natura‐α via regulation of Th‐1/Th‐17 responses

Cytokines and CD4⁺ Th cells play a crucial role in the pathogenesis of rheumatoid arthritis. Among the Th populations, Th‐1 and Th‐17 have been described as pathogenic in collagen‐induced arthritis (CIA) whereas Th‐2 and Treg were found to have protective effects. The objective of this study was to examine the affect of Natura‐α, a newly developed cytokine regulator, on CIA and on Th cell development. Natura‐α treatment was administered before or during arthritis induction. Anti‐type II collagen antibodies and cytokine expression were evaluated by ELISA. Emergence of CD4⁺CD25⁺Foxp3⁺ T cells was assessed by flow cytometry. Th‐17 differentiation of naive CD4 T cells was assessed in cultures with anti‐CD3 and anti‐CD28. We showed that Natura‐α both prevented and treated CIA. We further demonstrated that in vivo treatment with Natura‐α inhibited IL‐17 production and anti‐type II collagen IgG development. We showed in vitro, using an APC‐free system, that Natura‐α acted directly on differentiating T cells and inhibiting the formation of Th‐1 and Th‐17 cells but did not affect Th‐2 cells. Since Natura‐α inhibits a large spectrum of important pathogenic factors in CIA, it may provide a new and powerful approach to the treatment of rheumatoid arthritis and other inflammatory diseases.     

Mesenchymal Stem Cells Overexpressing Interleukin‐35 Propagate Immunosuppressive Effects in Mice

To explore generation of interleukin (IL)‐35‐expressing mouse adipocyte‐derived mesenchymal stem cells (Ad‐MSCs) using lentiviral vector and their potential immunosuppressive effects in mice. Ad‐MSCs were isolated and cultured in vitro and transfected with a lentivirus vector for overexpression of the therapeutic murine IL‐35 gene. IL‐35 expression in transfected MSCs (IL‐35‐MSCs) was quantified by enzyme‐linked immunosorbent assay (ELISA). The lymphocytes subsets after one‐way mixed lymphocyte culture and in vivo intravenous transplantation were analysed by flow cytometry to evaluate the immunosuppressive effects of IL‐35‐MSCs. ELISA was performed to examine IL‐10, IL‐17A and IL‐35 expression in lymphocyte culture. Mouse Ad‐MSCs were isolated and cultured. IL‐35 was expressed in the MSC supernatant and serum after IL‐35 transduction into Ad‐MSCs by lentiviral vector transfection in vitro and in vivo. The percentage of CD4⁺ CD25⁺ T regulatory (Treg) cells in mice treated with IL‐35‐MSCs significantly increased. IL‐35‐MSCs upregulated the CD4⁺ CD25⁺ Treg cells in the allogeneic mixed lymphocyte reaction system, and lowered the percentage of CD4⁺ T cells compared with the other two control groups (P < 0.01). IL‐17A expression significantly decreased and IL‐10 expression significantly increased in IL‐35‐MSCs and MSCs when compared by ELISA to the control groups (P < 0.01). IL‐35‐transduced Ad‐MSCs in vivo can enhance proliferation of CD4⁺ CD25⁺ Treg cells and suppress the function of effector T cells such as T helper (Th) 1, Th2 and Th17 cells and may reduce the development of allograft rejection. Our data suggest that transduced Ad‐MSCs overexpressing IL‐35 may provide a useful approach for basic research on cell‐based immunotolerance therapy for inducing transplantation tolerance.     

CXCL4 is a novel inducer of human Th17 cells and correlates with IL‐17 and IL‐22 in psoriatic arthritis

CXCL4 regulates multiple facets of the immune response and is highly upregulated in various Th17‐associated rheumatic diseases. However, whether CXCL4 plays a direct role in the induction of IL‐17 production by human CD4⁺ T cells is currently unclear. Here, we demonstrated that CXCL4 induced human CD4⁺ T cells to secrete IL‐17 that co‐expressed IFN‐γ and IL‐22, and differentiated naïve CD4⁺ T cells to become Th17‐cytokine producing cells. In a co‐culture system of human CD4⁺ T cells with monocytes or myeloid dendritic cells, CXCL4 induced IL‐17 production upon triggering by superantigen. Moreover, when monocyte‐derived dendritic cells were differentiated in the presence of CXCL4, they orchestrated increased levels of IL‐17, IFN‐γ, and proliferation by CD4⁺ T cells. Furthermore, the CXCL4 levels in synovial fluid from psoriatic arthritis patients strongly correlated with IL‐17 and IL‐22 levels. A similar response to CXCL4 of enhanced IL‐17 production by CD4⁺ T cells was also observed in patients with psoriatic arthritis. Altogether, we demonstrate that CXCL4 boosts pro‐inflammatory cytokine production especially IL‐17 by human CD4⁺ T cells, either by acting directly or indirectly via myeloid antigen presenting cells, implicating a role for CXCL4 in PsA pathology.     

Expression of IL‐15RA or an IL‐15/IL‐15RA fusion on CD8+ T cells modifies adoptively transferred T‐cell function in cis

IL‐15 and IL‐15 receptor alpha (IL‐15RA) play a significant role in multiple aspects of T‐cell biology. However, given the evidence that IL‐15RA can present IL‐15 in trans, the functional capacity of IL‐15RA expressed on CD8⁺ T cells to modify IL‐15 functions in cis is currently unclear. In the current study, we explore the functional consequences of IL‐15RA, expression on T cells using a novel method to transfect naive CD8⁺ T cells. We observed that RNA nucleofection led to highly efficient, non‐toxic, and rapid manipulation of protein expression levels in unstimulated CD8⁺ T cells. We found that transfection of unstimulated CD8⁺ T cells with IL‐15RA RNA led to enhanced viability of CD8⁺ T cells in response to IL‐15. Transfection with IL‐15RA enhanced IL‐15‐mediated phosphorylation of STAT5 and also promoted IL‐15‐mediated proliferation in vivo of adoptively transferred naïve CD8⁺ T cells. We demonstrated that IL‐15RA can present IL‐15 via cis‐presentation on CD8⁺ T cells. Finally, we showed that transfection with a chimeric construct linking IL‐15 to IL‐15RA cell autonomously enhances the viability and proliferation of primary CD8⁺ T cells and cytotoxic potential of antigen‐specific CD8⁺ T cells. The clinical implications of the current study are discussed.     

Inhibition of cardiac allograft rejection in mice using interleukin‐35‐modified mesenchymal stem cells

Interleukin‐35 (IL‐35) is a cytokine recently discovered to play a potent immunosuppressive role by intensifying the functions of regulatory T cells and inhibiting the proliferation and functions of T helper 1 and T helper 17 cells. Mesenchymal stem cells (MSCs) have recently emerged as promising candidates for cell‐based immune therapy, and our previous study showed that IL‐35 gene modification can effectively enhance the therapeutic effect of MSCs in vitro. In this study, we isolated adipose tissue‐derived MSCs in vitro and infected them with lentiviral vectors overexpressing the IL‐35 gene, thereby creating IL‐35‐MSCs. Subsequently, IL‐35‐MSCs were then injected into mice of the allogeneic heterotopic abdominal heart transplant model to determine their effect on allograft rejection. The results showed that IL‐35‐MSCs could continuously secrete IL‐35 in vivo and in vitro, successfully alleviate allograft rejection and prolong graft survival. In addition, compared to MSCs, IL‐35‐MSCs showed a stronger immunosuppressive ability and further reduced the percentage of Th17 cells, increased the proportion of CD4⁺ Foxp3⁺ T cells, and regulated Th1/Th2 balance in heart transplant mice. These findings suggest that IL‐35‐MSCs have more advantages than MSCs in inhibiting graft rejection and may thus provide a new approach for inducing immune tolerance during transplantation.     

IL‐21 promotes the production of anti‐DNA IgG but is dispensable for kidney damage in lyn−/− mice

The autoimmune disease systemic lupus erythematosus is characterized by loss of tolerance to nuclear Ags and a heightened inflammatory environment, which together result in end organ damage. Lyn‐deficient mice, a model of systemic lupus erythematosus, lack an inhibitor of B‐cell and myeloid cell activation. This results in B‐cell hyper‐responsiveness, plasma cell accumulation, autoantibodies, and glomerulonephritis (GN). IL‐21 is associated with autoimmunity in mice and humans and promotes B‐cell differentiation and class switching. Here, we explore the role of IL‐21 in the autoimmune phenotypes of lyn^–/– mice. We find that IL‐21 mRNA is reduced in the spleens of lyn^–/–IL‐6^–/– and lyn^–/–Btk^lo mice, neither of which produce pathogenic autoantibodies or develop significant GN. While IL‐21 is dispensable for plasma cell accumulation and IgM autoantibodies in lyn^–/– mice, it is required for anti‐DNA IgG antibodies and some aspects of T‐cell activation. Surprisingly, GN still develops in lyn^–/–IL‐21^–/– mice. This likely results from the presence of IgG autoantibodies against a limited set of non‐DNA Ags. These studies identify a specific role for IL‐21 in the class switching of anti‐DNA B cells and demonstrate that neither IL‐21 nor anti‐DNA IgG is required for kidney damage in lyn^–/– mice.     

Protein tyrosine phosphatase PTPN22 regulates IL‐1β dependent Th17 responses by modulating dectin‐1 signaling in mice

A single nucleotide polymorphism within the PTPN22 gene is a strong genetic risk factor predisposing to the development of multiple autoimmune diseases. PTPN22 regulates Syk and Src family kinases downstream of immuno‐receptors. Fungal β‐glucan receptor dectin‐1 signals via Syk, and dectin‐1 stimulation induces arthritis in mouse models. We investigated whether PTPN22 regulates dectin‐1 dependent immune responses. Bone marrow derived dendritic cells (BMDCs) generated from C57BL/6 wild type (WT) and Ptpn22^?/? mutant mice, were pulsed with OVA_323‐339 and the dectin‐1 agonist curdlan and co‐cultured in vitro with OT‐II T‐cells or adoptively transferred into OT‐II mice, and T‐cell responses were determined by immunoassay. Dectin‐1 activated Ptpn22^?/? BMDCs enhanced T‐cell secretion of IL‐17 in vitro and in vivo in an IL‐1β dependent manner. Immunoblotting revealed that compared to WT, dectin‐1 activated Ptpn22^?/? BMDCs displayed enhanced Syk and Erk phosphorylation. Dectin‐1 activation of BMDCs expressing Ptpn22^R619W (the mouse orthologue of human PTPN22^R620W) also resulted in increased IL‐1β secretion and T‐cell dependent IL‐17 responses, indicating that in the context of dectin‐1 Ptpn22^R619W operates as a loss‐of‐function variant. These findings highlight PTPN22 as a novel regulator of dectin‐1 signals, providing a link between genetically conferred perturbations of innate receptor signaling and the risk of autoimmune disease.     

Prediction of disease severity in neuromyelitis optica by the levels of interleukin (IL)‐6 produced during remission phase

T helper type 17 (Th17) cytokines have been implicated in the pathogenesis of neuromyelitis optica (NMO). As humanized anti‐interleukin (IL)‐6R (tocilizumab) immunoglobulin (Ig)G has been used as disease‐modifying therapy for NMO, the objective of our study was to investigate the role of endogenous IL‐6 on NMO‐derived CD4⁺ T cell behaviour. High production of IL‐6, IL‐17 and IL‐21 by CD4⁺ T‐cells was detected in NMO patients. Further, IL‐21 and IL‐6 levels were related directly to the level of neurological disabilities. The addition of anti‐IL‐6R IgG not only reduced directly the production of these cytokines, but also almost abolished the ability of activated autologous monocytes in enhancing IL‐6, IL‐17 and IL‐21 release by CD4⁺ T cells. In contrast, the production of IL‐10 was amplified in those cell cultures. Further, anti‐IL‐6R monoclonal antibodies (mAb) also potentiated the ability of glucocorticoid in reducing Th17 cytokines. Finally, the in‐vivo and in‐vitro IL‐6 levels were significantly higher among those patients who experienced clinical relapse during 2‐year follow‐up. In summary, our results suggest a deleterious role of IL‐6 in NMO by favouring, at least in part, the expansion of corticoid‐resistant Th17 cells.     

Expansion of regulatory T cells via IL‐2/anti‐IL‐2 mAb complexes suppresses experimental myasthenia

Human autoimmune diseases are often characterized by a relative deficiency in CD4⁺CD25⁺ regulatory T cells (Treg). We therefore hypothesized that expansion of Treg can ameliorate autoimmune pathology. We tested this hypothesis in an experimental model for autoimmune myasthenia gravis (MG), a B‐cell‐mediated disease characterized by auto‐Ab directed against the acetylcholine receptor within neuromuscular junctions. We showed that injection of immune complexes composed of the cytokine IL‐2 and anti‐IL‐2 mAb (JES6‐1A12) induced an effective and sustained expansion of Treg, via peripheral proliferation of CD4⁺CD25⁺Foxp3⁺ cells and peripheral conversion of CD4⁺CD25^?Foxp3^? cells. The expanded Treg potently suppressed autoreactive T‐ and B‐cell responses to acetylcholine receptor and attenuated the muscular weakness that is characteristic of MG. Thus, IL‐2/anti‐IL‐2 mAb complexes can expand functional Treg in vivo, providing a potential clinical application of this modality for treatment of MG and other autoimmune disorders.     

APRIL (TNFSF13) regulates collagen‐induced arthritis,IL‐17 production and Th2 response

A proliferation‐inducing ligand (APRIL or TNFSF13) shares receptors with B‐cell activation factor of the TNF family (BAFF) on B and T cells. Although much is known about the function of APRIL in B cells, its role in T cells remains unclear. Blocking both BAFF and APRIL suggested that BAFF and/or APRIL contributed to collagen‐induced arthritis (CIA); however, the role of APRIL alone in CIA remained unresolved. We show here that, in vitro, our newly generated APRIL^?/? mice exhibited increased T‐cell proliferation, enhanced Th2 cytokine production under non‐polarizing conditions, and augmented IL‐13 and IL‐17 production under Th2 polarizing conditions. Upon immunization with OVA and aluminum potassium sulfate, APRIL^?/? mice responded with an increased antigen‐specific IgG1 response. We also show that in APRIL^?/? mice, the incidence of CIA was significantly reduced compared with WT mice in parallel with diminished levels of antigen‐specific IgG2a autoantibody and IL‐17 production. Our data indicate that APRIL plays an important role in the regulation of cytokine production and that APRIL‐triggered signals contribute to arthritis. Blockade of APRIL thus may be a valuable adjunct in the treatment of rheumatoid arthritis.     

Interleukin‐27 suppresses osteoclastogenesis via induction of interferon‐γ

Interleukin (IL)‐27 is a heterodimeric cytokine that is known to have both stimulatory and inhibitory functions during immune responses. We investigated the effects of IL‐27 on arthritis and bone erosion in the murine collagen‐induced arthritis (CIA) model. We demonstrate that the inhibitory effect of IL‐27 on osteoclastogenesis is associated with interferon‐γ (IFN‐γ) production by using an IFN‐γ knockout mouse model. The IL‐27‐Fc was injected into both CIA and IFN‐γ‐deficient mice. The effects of IL‐27‐Fc on osteoclast differentiation were evaluated both in vitro and in vivo. The IL‐27‐Fc‐injected mice showed significantly lower arthritis indices and fewer tartrate‐resistant acid‐phosphatase‐positive osteoclasts in their joint tissues than untreated mice. Interleukin‐27 inhibited osteoclastogenesis from bone marrow‐derived mononuclear cells in vitro, which was counteracted by the addition of anti‐IFN‐γ antibody. The IL‐27‐Fc did not affect arthritis in IFN‐γ knockout mice. Interleukin‐27 also suppressed osteoclast differentiation in human and intriguingly, it could promote the expression of IFN‐γ on priming osteoclasts. These results imply that IL‐27 suppressed the generation of CIA and osteoclastogenesis, which were mediated by the induction of IFN‐γ.     

Regulatory effects of IFN‐β on production of osteopontin and IL‐17 by CD4+ T Cells in MS

IFN‐β currently serves as one of the major treatments for MS. Its anti‐inflammatory mechanism has been reported as involving a shift in cytokine balance from Th1 to Th2 in the T‐cell response against elements of the myelin sheath. In addition to the Th1 and Th2 groups, two other important pro‐inflammatory cytokines, IL‐17 and osteopontin (OPN), are believed to play important roles in CNS inflammation in the pathogenesis of MS. In this study, we examined the potential effects of IFN‐β on the regulation of OPN and IL‐17 in MS patients. We found that IFN‐β used in vitro at 0.5–3 ng/mL significantly inhibited the production of OPN in primary T cells derived from PBMC. The inhibition of OPN was determined to occur at the CD4⁺ T‐cell level. In addition, IFN‐β inhibited the production of IL‐17 and IL‐21 in CD4⁺ T cells. It has been described that IFN‐β suppresses IL‐17 production through the inhibition of a monocytic cytokine, the intracellular translational isoform of OPN. Our further investigation demonstrated that IFN‐β also acted directly on the CD4⁺ T cells to regulate OPN and IL‐17 expression through the type I IFN receptor‐mediated activation of STAT1 and suppression of STAT3 activity. Administration of IFN‐β to EAE mice ameliorated the disease severity. Furthermore, spinal cord infiltration of OPN⁺ and IL‐17⁺ cells decreased in IFN‐β‐treated EAE mice along with decreases in serum levels of OPN and IL‐21. Importantly, decreased OPN production by IFN‐β treatment contributes to the reduced migratory activity of T cells. Taken together, the results from both in vitro and in vivo experiments indicate that IFN‐β treatment can down‐regulate the OPN and IL‐17 production in MS. This study provides new insights into the mechanism of action of IFN‐β in the treatment of MS.