Essentiality of Nfatc1 short isoform in osteoclast differentiation and its self-regulation.

During osteoclast differentiation, the expression of the transcription factor nuclear factor of activated T cell 1 (Nfatc1) increases in an autoproliferative manner. Nfatc1 isoforms are of three sizes, and only the short isoform increases during osteoclast differentiation. Genetic ablation of the whole Nfatc1 gene demonstrated that it is essential for osteoclastogenesis; however, the specific role of the Nfatc1 short form (Nfatc1/αA) remains unknown. In this study, we engineered Nfatc1 short form-specific knockout mice and found that these mice died in utero by day 13.5. We developed a novel osteoclast culture system in which hematopoietic stem cells were cultured, proliferated, and then differentiated into osteoclasts in vitro. Using this system, we show that the Nfatc1/αA isoform is essential for osteoclastogenesis and is responsible for the expression of various osteoclast markers, the Nfatc1 short form itself, and Nfatc1 regulators.

Potential role of type I interferon/IP-10 axis in the pathogenesis of anti-MDA5 antibody-positive dermatomyositis.

OBJECTIVES: Dermatomyositis (DM) patients with anti-melanoma differentiation-associated protein 5 (MDA5) antibodies are known for poor prognosis. This study was designed to identify humoral factors that are readily detectable in the disease and may reflect its activity and pathophysiology. METHODS: We first quantified the serum level expression of 28 cytokines in the serum of patients with collagen vascular diseases using bead-based multiplex immunoassays. We completed these evaluations at hospital admission and followed up with three DM patients with anti-MDA5 antibodies during hospitalisation. We also performed an immunohistochemical analysis of skin samples obtained from two patients. RESULTS: The serum level of interferon gamma-induced protein 10 (IP-10) was significantly higher in DM patients with anti-MDA5 antibodies than in those without the antibody, decreasing drastically upon treatment. Interestingly, this time course paralleled not that of interferon (IFN)-γ, which was originally reported to be the inducer of IP-10, but that of IFN-α2. Immunohistochemical analysis revealed that most of the IP-10-positive cells were macrophages. Furthermore, monocytes stimulated with type I IFN in vitro produced IP-10 in a dose-dependent manner. CONCLUSIONS: IP-10 is a potentially useful disease activity marker of DM with anti-MDA5 antibodies, correlating more with IFN-α2 then IFN-γ. IP-10 released from macrophages might prompt the infiltration of macrophages themselves. Thus, the type I IFN/IP-10 axis may play a pivotal role in the pathogenesis of this intractable disease.

Transition from epoprostenol to selexipag in a patient with systemic sclerosis and pulmonary hypertension during the postoperative period of colon cancer surgery: A case report.

Introduction: Most pulmonary vasodilators are administered orally; however, in patients with pulmonary hypertension undergoing gastrointestinal surgery, a switch to parenteral drugs is needed. Parenteral pulmonary vasodilators carry a risk of infection and reduced quality of life owing to long-term central venous catheterization; therefore, it is preferable to switch them to oral vasodilators after surgery. Here, we present the case of a patient with systemic sclerosis complicated by pulmonary hypertension and colon cancer, for which treatment was successfully switched from epoprostenol to selexipag postoperatively. Case Description: A 59-year-old woman, who was diagnosed with mixed group I and III pulmonary hypertension and systemic sclerosis, was on oral triple pulmonary vasodilators for pulmonary hypertension and Raynaud's phenomenon. She was diagnosed as having colon cancer 3 months before admission. Despite the severe pulmonary condition and treatment with oral triple pulmonary vasodilators, colon cancer resection surgery was performed with the management for pulmonary hypertension through multidisciplinary treatments in collaboration with cardiology specialists. Medications for patients with pulmonary hypertension undergoing gastrointestinal surgery need to be switched from oral vasodilators to epoprostenol perioperatively. On postoperative day 19, 0.4 mg/day of selexipag was administered with epoprostenol. Subsequently, the epoprostenol dosage was gradually decreased, and selexipag was increased. On postoperative day 30, the dose of selexipag was increased to 1.2 mg/day and epoprostenol was discontinued. The patient was discharged on postoperative day 40. Conclusion: In our case, transition from epoprostenol to selexipag contributed to a more useful management strategy for systemic sclerosis and pulmonary hypertension in the postoperative period.

Immune Reconstitution Inflammatory Syndrome Associated with Pneumocystis jirovecii Pneumonia and Cytomegalovirus Colitis in a Patient with Rheumatoid Arthritis.

A 68-year-old woman presenting with rheumatoid arthritis was admitted due to pancytopenia caused by methotrexate. Pneumocystis jirovecii pneumonia was diagnosed based on the abnormal shadows observed on chest computed tomography, the presence of serum ß-D-glucan, and positive P. jirovecii-DNA results in a sputum analysis. Subsequently, after treatment with leucovorin and trimethoprim-sulfamethoxazole, lung consolidation was found to be aggravated, along with a rapidly increasing leukocyte count. In addition, cytomegalovirus colitis was diagnosed. Both conditions were associated with immune reconstitution inflammatory syndrome caused by recovery from leukopenia. The patient was successfully treated with intravenous methylprednisolone pulse therapy and ganciclovir.

Epstein-Barr virus encephalitis in a patient with rheumatoid arthritis.

A 53-year-old woman with a 6-year history of rheumatoid arthritis (RA) presented with pharyngeal pain, fever, and altered mental status. The patient had been treated with methotrexate (MTX) 12 mg/week, baricitinib 4 mg/day, and tacrolimus 2 mg/day. Magnetic resonance imaging of the brain revealed diffuse high-intensity lesions in the cerebral white matter, basal ganglia, brainstem, and right cerebellar hemisphere. She was diagnosed with Epstein-Barr virus (EBV) encephalitis due to elevated levels of EBV-DNA in the cerebrospinal fluid and serum. Although MTX-associated lymphoproliferative disorders are well-known complications in patients with RA, EBV encephalitis requires careful attention for such patients undergoing treatment with multiple potent immunosuppressants.

Dual effects of interleukin-10 on natural killer cells and monocytes and the implications for adult-onset Still's disease.

OBJECTIVES: We compared the serum levels of multiple cytokines in patients with adult-onset Still's disease (AOSD) and healthy controls to assess the effects of humoral factors on natural killer (NK) cells and monocytes. METHODS: We quantified the serum levels of 10 cytokines in the patients using bead-based multiplex immunoassays, along with interleukin (IL-)18 using ELISA. We then sorted NK cells and monocytes from the peripheral blood mononuclear cells (PBMCs) of healthy volunteers, cultured them in the presence or absence of cytokines that were detected in some or all of the serum samples from the AOSD patients and their combinations in vitro, and analysed the culture supernatant. RESULTS: IL-6 and IL-18 were the main cytokines increased in the serum of AOSD patients. When NK cells were cultured with the cytokines and IL-10, the combination of IL-10 and IL-18 substantially induced interferon (IFN-)γ. IL-6 had little effect on NK cells, probably because they barely expressed the IL-6 receptor and glycoprotein 130 (gp130). IFN-γ induced monocytes to produce IL-1ß, IL-6 and tumour necrosis factor (TNF-)α whereas IL-10 inhibited the induction of these proinflammatory cytokines. CONCLUSIONS: IL-10 evidently has dual effects on NK cells (stimulation) and on monocytes (inhibition). Better understanding the roles of the cytokine network would shed light on the pathogenesis of AOSD.

Characterization and Function of Tumor Necrosis Factor and Interleukin-6-Induced Osteoclasts in Rheumatoid Arthritis.

OBJECTIVE: We have previously reported that stimulation of mouse bone marrow-derived macrophages with tumor necrosis factor (TNF) and interleukin-6 (IL-6) induces differentiation of osteoclast-like cells. We undertook this study to clarify the characterization and function of human TNF and IL-6-induced osteoclasts using peripheral blood collected from patients with rheumatoid arthritis (RA) and healthy donors. METHODS: Peripheral blood monocytes were cultured with a combination of TNF and IL-6, TNF alone, IL-6 alone, or with RANKL, and their bone resorption ability was evaluated. Expression levels of NFATc1, proinflammatory cytokines, and matrix metalloproteinase 3 were analyzed. The effects of NFAT inhibitor and JAK inhibitor were examined. Furthermore, the relationship between the number of TNF and IL-6-induced osteoclasts or RANKL-induced osteoclasts differentiated from peripheral blood mononuclear cells (PBMCs) in patients with RA and the modified total Sharp score (mTSS) or whole-body bone mineral density (BMD) was examined. RESULTS: Peripheral blood monocytes stimulated with a TNF and IL-6-induced osteoclasts were shown to demonstrate the ability to absorb bone matrix. Cell differentiation was not inhibited by the addition of osteoprotegerin. Stimulation with a combination of TNF and IL-6 promoted NFATc1 expression, whereas the NFAT and JAK inhibitors prevented TNF and IL-6-induced osteoclast formation. Expression levels of IL1ß, TNF, IL12p40, and MMP3 were significantly increased in TNF and IL-6-induced osteoclasts, but not in RANKL-induced osteoclasts. The number of TNF and IL-6-induced osteoclasts differentiated from PBMCs in patients with RA positively correlated with the mTSS, whereas RANKL-induced osteoclast numbers negatively correlated with the whole-body BMD of the same patients. CONCLUSION: Our results demonstrate that TNF and IL-6-induced osteoclasts may contribute to the pathology of inflammatory arthritis associated with joint destruction, such as RA.

Treatment of psoriatic arthritis complicated by systemic lupus erythematosus with the IL-17 blocker secukinumab and an analysis of the serum cytokine profile.

Psoriasis is a chronic disease of the skin that often affects the joints (psoriatic arthritis, PsA). Biologic agents such as TNF-α, IL-23 and IL-17 blockers have been proven to be quite effective against psoriasis and PsA, indicating the importance of those cytokines in the pathogenesis of the diseases. The importance of the IL-23/IL-17 axis has also been reported in systemic lupus erythematosus (SLE), but the safety and effectiveness of IL-17 blockers in SLE remain largely unknown. We encountered a patient with PsA and SLE. We treated him with an IL-17 blocker, secukinumab, and quantified the serum levels of various cytokines before and after the initiation of secukinumab therapy. As expected, the treatment was effective against the symptoms of PsA. No serious adverse events were observed in terms of SLE. Interestingly, serum IL-6 was substantially decreased after the initiation of therapy, whereas serum IL-17 was under the detection limit. These data indicate that IL-17 is produced locally, upstream of IL-6 production.

Risk factors correlated with immunosuppressant discontinuation in antineutrophil cytoplasmic antibody-associated vasculitis patients.

AIM: The use of an immunosuppressant is recommended as a treatment for remission induction in anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV). However, the immunosuppressant is sometimes discontinued due to an adverse event. We sought to identify the cause and risk factors for immunosuppressant discontinuation in patients with AAV receiving remission induction treatment. METHODS: We retrospectively analyzed the cases of AAV patients treated in 2005-2016 with immunosuppressants to induce remission. We defined "discontinuation" as stopping, switching, or delaying immunosuppressant administration due to adverse events. We performed a multivariate analysis to identify risk factors for immunosuppressant discontinuation. RESULTS: We identified 50 patients treated with an immunosuppressant for remission induction: cyclophosphamide was used in 45 patients (90%), methotrexate in 4 (8%), and cyclosporine A in 1 patient (2%). Among them, 26 patients (52%) underwent discontinuation of the immunosuppressant. Infection and myelosuppression were the major causes of discontinuation. Multivariate Cox proportional hazards regression analysis revealed that a cumulative dose of prednisolone ≥ 2000 mg (hazard ratio [HR] =2.18, 95% confidence interval [CI] =1.37-3.70, P < .001), performance status of 3-4 (HR = 1.80, 95% CI = 1.07-3.03, P = .027), and oral cyclophosphamide (HR = 1.81, 95% CI = 1.11-2.97, P = .018) were independent risk factors correlated with immunosuppressant discontinuation. CONCLUSION: Physicians should be aware of risk factors predicting immunosuppressant discontinuation when treating AAV patients with an immunosuppressant.

Salmonella enterica Subspecies arizonae Detected from Bilateral Pleural Fluid in a Patient with Systemic Lupus Erythematosus and Malignant Lymphoma.

A 72-year-old woman was admitted to our hospital with bilateral pleural effusions. She had a 31-year history of systemic lupus erythematosus and had been treated with prednisolone and azathioprine. Pleural fluid culture revealed Salmonella enterica subsp. arizonae infection. This pathogen rarely infects humans but is commonly found in the gut flora of reptiles, especially snakes. Our patient had not come in contact with reptiles. Despite antibiotic therapies and negative pleural cultures, the pleural effusion persisted. Colon cancer was detected concomitantly, and she finally died. The autopsy revealed that the pleuritis was due to underlying diffuse large B cell lymphoma.

A Non-smoking Woman with Anti-phospholipid Antibodies Proved to Have Thromboangiitis Obliterans.

A 48-year-old woman with severe pain and numbness of her right leg and foot was admitted to our hospital. She had never smoked and had little exposure to passive smoking. Initially, polyarteritis nodosa with anti-phospholipid antibodies was considered. Combination therapy with methylprednisolone pulse therapy, intravenous cyclophosphamide pulse therapy, vasodilators, antiplatelet agents, and anticoagulants was not effective. Vasculopathy was progressive, and she presented with gangrene of the toes. She required amputation of her right leg. The pathological findings of the amputated leg revealed thromboangiitis obliterans (TAO). TAO should be considered even in non-smoking women. Non-response to immunosuppressant and anticoagulant therapies may be a clue to the diagnosis of TAO.

Change in smoking cessation stage over 1 year in patients with schizophrenia: a follow up study in Japan.

BACKGROUND: We performed a follow up study about willingness and behaviors to quit smoking among smokers with schizophrenia in Japan. METHODS: Participants were outpatients with schizophrenia aged 20-69 years who had been visiting the hospital for ≥1 year as of April 1, 2016, and had visited the hospital more than once in the previous 6 months. A baseline survey on smoking behaviors including current smoking status and smoking cessation stage, was administered in 420 participants that were randomly extracted from a patient pool (n = 680) in 2016, and a follow-up survey was administered in 2017. We calculated the distribution and change in smoking cessation stage, number of smokers and nonsmokers after 1 year, and quitting rate from a naturalistic 1-year smoking-cessation follow up. RESULTS: The number of baseline respondents was 350; 113 current smokers and 68 former smokers. Among the 113 current smokers, 104 (92.0%) were followed for 1 year, 79 (70.0%) were interested in smoking cessation, and only 7 had received smoking cessation treatments at baseline. Among the tracked 104 participants, only 6 (5.8%) stopped smoking after 1 year. Among the 25 participants who had intentions to quit smoking within 6 months at baseline, 6 (24.0%) maintained their intention to quit smoking for 1 year, and 16 (64.0%) did not maintain their intention to quit smoking. CONCLUSIONS: Our findings showed that many smokers with schizophrenia were interested in quitting smoking, but few patients received treatment and actually quit smoking. Timely intervention, including the option to receive smoking cessation treatment, is necessary for those patients with schizophrenia who smoke. TRIAL REGISTRATION: UMIN Clinical Trials Registry (UMIN000023874, registered on August 31, 2016).

Changes in the pattern of cytokine production from peripheral blood mononuclear cells in patients with rheumatoid arthritis treated with infliximab and their relation to plasma arginase activity.

AIM: The aim of this study was to quantify the production of T-cell cytokines from the peripheral blood mononuclear cells (PBMCs) of RA patients before and after treatment with anti-tumor necrosis factor (TNF)-α infliximab (IFX). METHOD: We stimulated the PBMCs of RA patients (n = 24) in vitro and quantified the cytokines in the culture supernatant using enzyme-linked immunosorbent assay. RESULTS: Unexpectedly, the cytokines tested, interferon (IFN)-γ, interleukin (IL)-4 and IL-17, were all found to have increased, rather than decreased, after the treatment. When the patients were divided into two groups according to the plasma activity of arginase, which is implicated in the immune-suppressive function of myeloid-derived suppressor cells, the substantial increase in the cytokine production ex vivo was only detected in the group in which the arginase activity was decreased after the treatment with IFX. In fact, although the ex vivo production of IL-21 increased along with the other cytokines, the plasma concentration of IL-21 decreased significantly after IFX treatment. CONCLUSION: It is important to exercise caution in interpreting ex vivo cytokine production data, in that they can be negatively influenced by the immune-suppressive mechanisms that prevent excessive inflammation. Thus, to analyze the T-cell response accurately, T-cell markers that are detectable in the serum or plasma need to be discovered. The concentrations of IFN-γ, IL-4 and IL-17 were all below detection limits, but that of IL-21 was detectable in the plasma and inversely correlated with the production of IL-21 ex vivo. This may indicate the involvement of Th17 response in the pathogenesis of RA.

Altered gene expression profiles of histone lysine methyltransferases and demethylases in rheumatoid arthritis synovial fibroblasts.

OBJECTIVES: Aberrant histone lysine methylation (HKM) has been reported in rheumatoid arthritis (RA) synovial fibroblasts (SFs). As histone lysine methyltransferases (HKMTs) and demethylases (HKDMs) regulate HKM, these enzymes are believed to be dysregulated in RASFs. The aim of this study is to clarify whether gene expressions of HKMTs and HKDMs are altered in RASFs. METHODS: SFs were isolated from synovial tissues obtained from RA or osteoarthritis (OA) patients during total knee joint replacement. The mRNA levels of 34 HKMTs and 22 HKDMs were examined after stimulation with tumour necrosis factor α (TNF-α) in RASFs and OASFs. RESULTS: The gene expression of the 12 HKMTs, including MLL1, MLL3, SUV39H1, SUV39H2, PRDM2, EZH2, SETD2, NSD2, NSD3, SMYD4, DOT1, and PR-set7, that catalyse the methylation of H3K4, H3K9, H3K27, H3K36, H3K79, or H4K20 was higher after TNFα stimulation in RASFs vs. OASFs. The gene expression of the 4 HKDMs, including FBXL10, NO66, JMJD2D, and FBXL11, that catalyse the methylation of H3K4, H3K9, or H3K36 was higher after TNFα stimulation in RASFs vs. OASFs. CONCLUSIONS: The study findings suggest that the HKM-modifying enzymes are involved in the alteration of HKM, which results in changes in the gene expression of RASFs.

A case of systemic lupus erythematosus with multiple nodules in the bilateral lungs and vertebrae.

We encountered a case of a middle-aged woman with systemic lupus erythematosus. As the patient had progressive peripheral neuropathy including foot drop, we intended to treat her with intensive immunosuppressive therapy as soon as possible. Pretreatment assessment, however, revealed multiple nodular lesions in the lungs and bones, suggesting disseminated tumor metastasis or miliary tuberculosis. To our surprise, gallium and bone scintigraphy as well as cytodiagnosis revealed no sign of malignancy or infection, leading us to suspect the presence of another multisystem disorder. The presence of subependymal nodules and a periungual fibroma strongly suggested tuberous sclerosis (TS). A genetic test revealed a mutation in the TSC1 gene and confirmed the diagnosis. Thus, the multiple nodular lesions were most likely a hyperplasia due to TS. Although the odds of a comorbidity of more than one multisystem disorder are considered to be quite low, it should be kept in mind that when such a situation does exist, the comorbidity may make the presenting symptoms extremely diverse.

Histone Methylation and STAT-3 Differentially Regulate Interleukin-6-Induced Matrix Metalloproteinase Gene Activation in Rheumatoid Arthritis Synovial Fibroblasts.

OBJECTIVE: Synovial fibroblasts (SFs) produce matrix-degrading enzymes that cause joint destruction in rheumatoid arthritis (RA). Epigenetic mechanisms play a pivotal role in autoimmune diseases. This study was undertaken to elucidate the epigenetic mechanism that regulates the transcription of matrix metalloproteinases (MMPs) in RASFs. METHODS: MMP gene expression and histone methylation profiles in the MMP promoters were examined in RASFs. The effect of WD repeat domain 5 (WDR5) silencing on histone methylation and MMP gene expression in RASFs was analyzed. MMP gene expression, surface expression of the interleukin-6 (IL-6) receptor, phosphorylation of STAT-3, and binding of STAT-3 in the MMP promoters were investigated in RASFs stimulated with IL-6. RESULTS: The MMP-1, MMP-3, MMP-9, and MMP-13 genes were actively transcribed in RASFs. Correspondingly, the level of histone H3 trimethylated at lysine 4 (H3K4me3) was elevated, whereas that of H3K27me3 was suppressed in the MMP promoters in RASFs. The decrease in H3K4me3 via WDR5 small interfering RNA reduced the levels of messenger RNA for MMP-1, MMP-3, MMP-9, and MMP-13 in RASFs. Interestingly, IL-6 signaling significantly increased the expression of MMP-1, MMP-3, and MMP-13, but not MMP-9, in RASFs. Although the IL-6 signaling pathway was similarly active in RASFs and osteoarthritis SFs, STAT-3 bound to the MMP-1, MMP-3, and MMP-13 promoters, but not the MMP-9 promoter, after IL-6 stimulation in RASFs. CONCLUSION: Our findings indicate that histone methylation and STAT-3 regulate spontaneous and IL-6-induced MMP gene activation in RASFs. The combination of chromatin structure and transcription factors may regulate distinct arthritogenic properties of RASFs.

A significant induction of neutrophilic chemoattractants but not RANKL in synoviocytes stimulated with interleukin 17.

Interleukin 17 (IL-17) is a cytokine implicated in the promotion of osteoclastogenesis. Its effect has been believed not to be directly exerted on osteoclast precursors, but rather indirectly carried out via an induction of receptor activator of NF-κB ligand (RANKL), the osteoclast differentiation factor, on osteoclast-supporting cells, which in turn exert an effect on osteoclast precursors. The mechanistic details, however, remain unclear. In this study, we first performed a transcriptome analysis of synoviocytes derived from a patient with rheumatoid arthritis cultured in the presence or absence of IL-17. We discovered that most of the genes significantly induced by IL-17 were chemokines with a chemotactic effect on neutrophils. We confirmed these results by quantitative RT-PCR and ELISA. Unexpectedly, the stimulation with IL-17 alone did not induce the expression of RANKL either at the mRNA or the protein level. The induction of RANKL was observed when IL-17 was added in combination with 1,25-dihydroxyvitamin D3 and prostaglandin E2, well-known inducers of RANKL, although the exact mechanism of this synergistic effect remains unclear. IL-6 and monocyte chemoattractant protein-1 were also significantly induced by IL-17 at both the mRNA and protein levels. Thus, it appears that IL-17 induces the migration of neutrophils and monocytes/macrophages through the activation of synoviocytes, and enhances a positive feedback loop composed of proinflammatory cytokines IL-6 and IL-17.

Aberrant histone acetylation contributes to elevated interleukin-6 production in rheumatoid arthritis synovial fibroblasts.

Accumulating evidence indicates that epigenetic aberrations have a role in the pathogenesis of rheumatoid arthritis (RA). However, reports on histone modifications are as yet quite limited in RA. Interleukin (IL)-6 is an inflammatory cytokine which is known to be involved in the pathogenesis of RA. Here we report the role of histone modifications in elevated IL-6 production in RA synovial fibroblasts (SFs). The level of histone H3 acetylation (H3ac) in the IL-6 promoter was significantly higher in RASFs than osteoarthritis (OA) SFs. This suggests that chromatin structure is in an open or loose state in the IL-6 promoter in RASFs. Furthermore, curcumin, a histone acetyltransferase (HAT) inhibitor, significantly reduced the level of H3ac in the IL-6 promoter, as well as IL-6 mRNA expression and IL-6 protein secretion by RASFs. Taken together, it is suggested that hyperacetylation of histone H3 in the IL-6 promoter induces the increase in IL-6 production by RASFs and thereby participates in the pathogenesis of RA.

Combination of tumor necrosis factor α and interleukin-6 induces mouse osteoclast-like cells with bone resorption activity both in vitro and in vivo.

OBJECTIVE: To clarify the function of osteoclast-like multinuclear cells differentiated from bone marrow-derived macrophages (BMMs) by a combination of tumor necrosis factor α (TNFα) and interleukin-6 (IL-6), and to investigate the molecular mechanisms underlying the differentiation. METHODS: BMMs were stimulated by TNFα and/or IL-6. The cells were then compared with conventional osteoclasts differentiated in vitro by RANKL. An in vitro pit formation assay on dentine slices and an in vivo resorption assay of calvarial bones were performed. We also evaluated the activities and expression levels of NF-κB, c-Fos, and NF-ATc1, which are essential to the differentiation of conventional osteoclasts. Small interfering RNA was used to knock down c-Fos. The effects of genetic ablation of STAT-3 and pharmacologic inhibitors of NF-AT, JAK, and ERK were also studied. RESULTS: Osteoclast-like cell differentiation depended on TNFα and IL-6 and was not inhibited by osteoprotegerin. These differentiated cells were associated with both in vitro and in vivo bone resorption activity. TNFα and IL-6 had a synergistic effect on the activity and expression of c-Fos. Knockdown of c-Fos inhibited the expression of NF-ATc1 and the differentiation of osteoclast-like cells. All of these inhibitors blocked differentiation of the cells in vitro, but surprisingly, the conditional knockout of STAT-3 did not. Tofacitinib also inhibited the bone destruction caused by TNFα and IL-6 in vivo. CONCLUSION: Our results demonstrate that a combination of the inflammatory cytokines TNFα and IL-6 can induce osteoclast-like cells that have in vitro and in vivo bone-resorptive activity.