Trained innate immunity modulates osteoblast and osteoclast differentiation

Macrophages are key regulators in bone repair and regeneration. Recent studies have shown that long-term epigenetic changes and metabolic shifts occur during specific immune training of macrophages that affect their functional state, resulting in heightened (trained) or reduced (tolerant) responses upon exposure to a second stimulus. This is known as innate immune memory. Here, we study the impact of macrophages' memory trait on osteoblast differentiation of human mesenchymal stromal cells (hMSCs) and osteoclast differentiation. An in vitro trained immunity protocol of monocyte-derived macrophages was employed using inactivated Candida albicans and Bacillus Calmette-Guérin (BCG) to induce a 'trained' state and Pam3CSK4 (PAM) and Lipopolysaccharides (LPS) to induce a 'tolerance' state. Macrophages were subsequently cocultured with hMSCs undergoing osteogenic differentiation during either resting (unstimulated) or inflammatory conditions (restimulated with LPS). Alkaline phosphatase activity, mineralization, and cytokine levels (TNF, IL-6, oncostatin M and SDF-1α) were measured. In addition, macrophages underwent osteoclast differentiation. Our findings show that trained and tolerized macrophages induced opposing results. Under resting conditions, BCG-trained macrophages enhanced ALP levels (threefold), while under inflammatory conditions this was found in the LPS-tolerized macrophages (fourfold). Coculture of hMSCs with trained macrophages showed mineralization while tolerized macrophages inhibited the process under both resting and inflammatory conditions. While osteoclast differentiation was not affected in trained-macrophages, this ability was significantly loss in tolerized ones. This study further confirms the intricate cross talk between immune cells and bone cells, highlighting the need to consider this interaction in the development of personalized approaches for bone regenerative medicine.

Evaluation and 1-year follow-up of patients presenting at a Lyme borreliosis expertise centre: a prospective cohort study with validated questionnaires

OBJECTIVES

To describe the course of symptoms reported by patients with symptoms attributed to Lyme borreliosis (LB) without being subsequently diagnosed with LB.

METHODS

We performed a prospective cohort study with patients presenting at the outpatient clinic of two clinical LB centres. The primary outcome was the prevalence of persistent symptoms, which were defined as clinically relevant fatigue (CIS, subscale fatigue), pain (SF-36, subscale bodily pain), and cognitive impairment (CFQ) for ≥ 6 months and onset < 6 months over the first year of follow-up. Outcomes were compared with a longitudinal cohort of confirmed LB patients and a general population cohort. Prevalences were standardised to the distribution of pre-defined confounders in the confirmed LB cohort.

RESULTS

Participants (n = 123) reported mostly fatigue, arthralgia, myalgia, and paraesthesia as symptoms. The primary outcome could be determined for 74.8% (92/123) of participants. The standardised prevalence of persistent symptoms in our participants was 58.6%, which was higher than in patients with confirmed LB at baseline (27.2%, p < 0.0001) and the population cohort (21.2%, p < 0.0001). Participants reported overall improvement of fatigue (p < 0.0001) and pain (p < 0.0001) but not for cognitive impairment (p = 0.062) during the follow-up, though symptom severity at the end of follow-up remained greater compared to confirmed LB patients (various comparisons p < 0.05).

CONCLUSION

Patients with symptoms attributed to LB who present at clinical LB centres without physician-confirmed LB more often report persistent symptoms and report more severe symptoms compared to confirmed LB patients and a population cohort.

Adipose tissue induces trained innate immunity in patients with obesity

Introduction

Obesity is the most prevalent modifiable risk factor for atherosclerotic cardiovascular disease and is characterized as a chronic inflammatory disease. Cells of the innate immune system, especially monocytes and macrophages, play a pivotal role in the various stages of atherosclerosis, although it still remains elusive why the strong inflammatory response persists in time. We recently showed that cells of the innate immune system, such as monocytes, can adopt a long-term immunological memory. Upon brief stimulation with atherogenic stimuli, monocytes demonstrate an enhanced long-term pro-inflammatory and pro-atherogenic phenotype. This is termed trained immunity and is mediated via epigenetic and metabolic reprogramming. The clinical relevance of these findings was verified in patients with symptomatic atherosclerosis, in which circulating monocytes showed a trained immune phenotype.

Purpose

As various adipose tissue-related particles, including pro-inflammatory cytokines and fatty acids, are capable of inducing trained immunity in vitro, we hypothesized that adipose tissue from obese subjects might induce training in peripheral monocytes, thereby contributing to the increased risk of atherosclerotic CVD in these patients. In line with this hypothesis, it is unclear whether chronic inflammation sustains after a previous period of obesity despite significant weight loss.

Methods

We obtained blood from 25 patients with obesity before and 6 months after bariatric surgery. Monocyte subsets and activation phenotype were studied using flow cytometry. Cytokine production capacity of isolated PBMCs was studied after ex vivo stimulation with several infectious and metabolic stimuli and we characterized isolated monocytes using transcriptomics. Next, we obtained visceral (VAT) and subcutaneous adipose tissue (SAT) biopsies from 10 patients. Using our established in vitro model for trained immunity, we co-incubated healthy human monocytes with the adipose tissue biopsies for 24 hours in a trans-well set-up. After 24 hours, the adipose tissue was removed and monocytes were rested. On day 6, the cells were re-stimulated for 24 hours with a second stimulus and cytokine production and the transcriptome of the macrophages was analyzed.

Results

Both SAT and VAT obtained from patients with obesity can induce a long-term memory in healthy human monocytes, as demonstrated by an increased cytokine production capacity 6 days after co-incubation. Interestingly, VAT induced a higher cytokine response compared to SAT. Analysis of the inflammatory phenotype of peripheral cells before and after bariatric surgery is currently ongoing.

Conclusions

Adipose tissue-secreted metabolites, particularly secreted by VAT, have the potential to induce persistent innate immune cell activation. Our further analyses will show whether the secretion of these molecules and the activation of the innate immune system persists upon weight loss.

Funding Acknowledgement

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Dutch Heart Foundation

Urate-induced epigenetic modifications in myeloid cells

OBJECTIVES

Hyperuricemia is a metabolic condition central to gout pathogenesis. Urate exposure primes human monocytes towards a higher capacity to produce and release IL-1β. In this study, we assessed the epigenetic processes associated to urate-mediated hyper-responsiveness.

METHODS

Freshly isolated human peripheral blood mononuclear cells or enriched monocytes were pre-treated with solubilized urate and stimulated with LPS with or without monosodium urate (MSU) crystals. Cytokine production was determined by ELISA. Histone epigenetic marks were assessed by sequencing immunoprecipitated chromatin. Mice were injected intraarticularly with MSU crystals and palmitate after inhibition of uricase and urate administration in the presence or absence of methylthioadenosine. DNA methylation was assessed by methylation array in whole blood of 76 participants with normouricemia or hyperuricemia.

RESULTS

High concentrations of urate enhanced the inflammatory response in vitro in human cells and in vivo in mice, and broad-spectrum methylation inhibitors reversed this effect. Assessment of histone 3 lysine 4 trimethylation (H3K4me3) and histone 3 lysine 27 acetylation (H3K27ac) revealed differences in urate-primed monocytes compared to controls. Differentially methylated regions (e.g. HLA-G, IFITM3, PRKAB2) were found in people with hyperuricemia compared to normouricemia in genes relevant for inflammatory cytokine signaling.

CONCLUSION

Urate alters the epigenetic landscape in selected human monocytes or whole blood of people with hyperuricemia compared to normouricemia. Both histone modifications and DNA methylation show differences depending on urate exposure. Subject to replication and validation, epigenetic changes in myeloid cells may be a therapeutic target in gout.

Mimicking Behçet's disease: GM-CSF gain of function mutation in a family suffering from a Behçet's disease-like disorder marked by extreme pathergy

Behçet's disease (BD) is an inflammatory disease mainly affecting men along the ancient Silk Route. In the present study we describe a Dutch family suffering from BD-like disease with extreme pathergic responses, but without systemic inflammation. Genetic assessment revealed a combination of the human leukocyte antigen (HLA)-B*51 risk-allele together with a rare heterozygous variant in the CSF2 gene (c.130A>C, p.N44H) encoding for granulocyte-macrophage colony-stimulating factor (GM-CSF) found by whole exome sequencing. We utilized an over-expression vector system in a human hepatocyte cell line to produce the aberrant variant of GM-CSF. Biological activity of the protein was measured by signal transducer and activator of transcription 5 (STAT-5) phosphorylation, a downstream molecule of the GM-CSF receptor, in wild-type peripheral mononuclear cells (PBMCs) using flow cytometry. Increased STAT-5 phosphorylation was observed in response to mutated GM-CSF when compared to the wild-type or recombinant protein. CSF2 p.N44H results in disruption of one of the protein's two N-glycosylation sites. Enzymatically deglycosylated wild-type GM-CSF also enhanced STAT-5 phosphorylation. The patient responded well to anti-tumor necrosis factor (TNF)-α treatment, which may be linked to the capacity of TNF-α to induce GM-CSF in phorbol 12-myristate 13-acetate (PMA)-treated PBMCs, while GM-CSF itself only induced dose-dependent interleukin (IL)-1Ra production. The identified CSF2 pathway could provide novel insights into the pathergic response of BD-like disease and offer new opportunities for personalized treatment.

A systems genomics approach identifies SIGLEC15 as a susceptibility factor in recurrent vulvovaginal candidiasis

Candida vaginitis is a frequent clinical diagnosis with up to 8% of women experiencing recurrent vulvovaginal candidiasis (RVVC) globally. RVVC is characterized by at least three episodes per year. Most patients with RVVC lack known risk factors, suggesting a role for genetic risk factors in this condition. Through integration of genomic approaches and immunological studies in two independent cohorts of patients with RVVC and healthy individuals, we identified genes and cellular processes that contribute to the pathogenesis of RVVC, including cellular morphogenesis and metabolism, and cellular adhesion. We further identified SIGLEC15, a lectin expressed by various immune cells that binds sialic acid-containing structures, as a candidate gene involved in RVVC susceptibility. Candida stimulation induced SIGLEC15 expression in human peripheral blood mononuclear cells (PBMCs) and a polymorphism in the SIGLEC15 gene that was associated with RVVC in the patient cohorts led to an altered cytokine profile after PBMC stimulation. The same polymorphism led to an increase in IL1B and NLRP3 expression after Candida stimulation in HeLa cells in vitro. Last, Siglec15 expression was induced by Candida at the vaginal surface of mice, where in vivo silencing of Siglec15 led to an increase in the fungal burden. Siglec15 silencing was additionally accompanied by an increase in polymorphonuclear leukocytes during the course of infection. Identification of these pathways and cellular processes contributes to a better understanding of RVVC and may open new therapeutic avenues.

Validation of cellular tests for Lyme borreliosis (VICTORY) study

Background

Lyme borreliosis (LB) is a tick-borne disease caused by spirochetes belonging to the Borrelia burgdorferi sensu lato species. Due to a variety of clinical manifestations, diagnosing LB can be challenging, and laboratory work-up is usually required in case of disseminated LB. However, the current standard of diagnostics is serology, which comes with several shortcomings. Antibody formation may be absent in the early phase of the disease, and once IgG-seroconversion has occurred, it can be difficult to distinguish between a past (cured or self-cleared) LB and an active infection. It has been postulated that novel cellular tests for LB may have both higher sensitivity earlier in the course of the disease, and may be able to discriminate between a past and active infection.

Methods

VICTORY is a prospective two-gate case-control study. We strive to include 150 patients who meet the European case definitions for either localized or disseminated LB. In addition, we aim to include 225 healthy controls without current LB and 60 controls with potentially cross-reactive conditions. We will perform four different cellular tests in all of these participants, which will allow us to determine sensitivity and specificity. In LB patients, we will repeat cellular tests at 6 weeks and 12 weeks after start of antibiotic treatment to assess the usefulness as ‘test-of-cure’. Furthermore, we will investigate the performance of the different cellular tests in a cohort of patients with persistent symptoms attributed to LB.

Discussion

This article describes the background and design of the VICTORY study protocol. The findings of our study will help to better appreciate the utility of cellular tests in the diagnosis of Lyme borreliosis.

Trial registration

NL7732 (Netherlands Trial Register, trialregister.nl).

Electronic supplementary material

The online version of this article (10.1186/s12879-019-4323-6) contains supplementary material, which is available to authorized users.

Non-specific effects of BCG in protozoal infections: tegumentary leishmaniasis and malaria

BACKGROUND

Leishmaniasis and malaria are major causes of illness in the poorest countries. In the absence of efficient strategies to prevent infections and to control the transmission of the parasites by insect vectors, treatment relies on drug therapy. Vaccine development continues on several fronts; however none of the candidates developed has so far been shown to provide long-lasting protection at a population level. Because the bacillus Calmette-Guérin (BCG) vaccine can induce heterologous protective effects, we hypothesize that BCG has beneficial effects in the control of tegumentary leishmaniasis (TL) and malaria.

AIMS

In this review we describe evidence for the protective efficacy of BCG against tegumentary leishmaniasis and malaria in humans.

SOURCES

Relevant data from peer-reviewed scientific literature published on Pubmed up to January 2019 were examined.

CONTENT

From experimental animal and various human studies with BCG and one recent randomized malaria trial there is evidence that BCG has beneficial effects in Leishmania spp. and Plasmodium falciparum infections. Although the precise mechanisms remain unknown, BCG can activate innate immune responses, and an increasing body of evidence demonstrates that the induction of trained innate immunity could explain its non-specific protective effects.

IMPLICATIONS

Despite many years of research to prevent and treat TL and malaria, these diseases remain a public health problem in tropical countries. Future studies are required to examine if BCG vaccination could be used as an effective treatment option.

Romidepsin suppresses monosodium urate crystal-induced cytokine production through upregulation of suppressor of cytokine signaling 1 expression

Background

Acute gouty arthritis currently is the most common form of inflammatory arthritis in developed countries. Treatment is still suboptimal. Dosage of urate-lowering therapy is often too low to reach target urate levels, and adherence to therapy is poor. In this study, we therefore explore a new treatment option to limit inflammation in acute gout: specific histone deacetylase (HDAC) inhibition.

Methods

Peripheral blood mononuclear cells (PBMCs) were cultured with a combination of monosodium urate crystals (MSU) and palmitic acid (C16.0) in order to activate the NLRP3 inflammasome and induce IL-1β production. HDAC inhibitors and other compounds were added beforehand with a 1-h pre-incubation period.

Results

The HDAC1/2 inhibitor romidepsin was most potent in lowering C16.0+MSU-induced IL-1β production compared to other specific class I HDAC inhibitors. At 10 nM, romidepsin decreased IL-1β, IL-1Ra, IL-6, and IL-8 production. IL-1β mRNA was significantly decreased at 25 nM. Although romidepsin increased PTEN expression, PBMCs from patients with germline mutations in PTEN still responded well to romidepsin. Romidepsin also increased SOCS1 expression and blocked STAT1 and STAT3 activation. Furthermore, experiments with bortezomib showed that blocking the proteasome reverses the cytokine suppression by romidepsin.

Conclusions

Our results show that romidepsin is a very potent inhibitor of C16.0+MSU-induced cytokines in vitro. Romidepsin upregulated transcription of SOCS1, which was shown to directly target inflammatory signaling molecules for proteasomal degradation. Inhibiting the proteasome therefore reversed the cytokine-suppressive effects of romidepsin. HDAC1/2 dual inhibition could therefore be a highly potent new treatment option for acute gout, although safety has to be determined in vivo.

Electronic supplementary material

The online version of this article (10.1186/s13075-019-1834-x) contains supplementary material, which is available to authorized users.

Role of gut microbiota in chronic low-grade inflammation as potential driver for atherosclerotic cardiovascular disease: a systematic review of human studies

A hallmark of obesity is chronic low-grade inflammation, which plays a major role in the process of atherosclerotic cardiovascular disease (ACVD). Gut microbiota is one of the factors influencing systemic immune responses, and profound changes have been found in its composition and metabolic function in individuals with obesity. This systematic review assesses the association between the gut microbiota and markers of low-grade inflammation in humans. We identified 14 studies which were mostly observational and relatively small (n = 10 to 471). The way in which the microbiome is analysed differed extensively between these studies. Lower gut microbial diversity was associated with higher white blood cell counts and high sensitivity C-reactive protein (hsCRP) levels. The abundance of Bifidobacterium, Faecalibacterium, Ruminococcus and Prevotella were inversely related to different markers of low-grade inflammation such as hsCRP and interleukin (IL)-6. In addition, this review speculates on possible mechanisms through which the gut microbiota can affect low-grade inflammation and thereby ACVD. We discuss the associations between the microbiome and the inflammasome, the innate immune system, bile acids, gut permeability, the endocannabinoid system and TMAO. These data reinforce the importance of human research into the gut microbiota as potential diagnostic and therapeutic strategy to prevent ACVD.

HDAC inhibitors modulate innate immune responses to micro-organisms relevant to chronic mucocutaneous candidiasis

Signal transducer and activator of transcription 1 (STAT-1) gain-of-function (GOF) mutations cause chronic mucocutaneous candidiasis (CMC), a disease associated with Candida albicans and Staphylococcus aureus infection. Patients suffer from dysegulated immune responses due to aberrant cell programming and function. We investigated the effect of inhibitory molecules targeting histone deacetylases (HDACi) on the immune responses of peripheral blood mononuclear cells (PBMCs) of healthy controls and patients with CMC towards microbes relevant for CMC. PBMCs cells were pretreated with HDACi and challenged with C. albicans or S. aureus. Innate and adaptive cytokines were measured in cell culture supernatants by enzyme-linked immunosorbent assay (ELISA). We assessed the effect of HDAC inhibitors on T helper type 1 (Th1) and Th17 cells and measured STAT-1 and STAT-3 phosphorylation using flow cytometry. Panobinostat, a pan-HDAC inhibitor, strongly inhibits innate and adaptive cytokines upon challenge with C. albicans or S. aureus. Specific inhibitors (entinostat or RGFP966) also had a tendency to lower production of most innate cytokines in CMC patient cells. Entinostat and RGFP966 increased the production of interleukin (IL)-22 specifically after S. aureus challenge in patient cells. In healthy and control cells, entinostat and RGFP966 treatment down-regulated STAT-1 phosphorylation while pSTAT-3 levels remained stable. HDACi modulate cytokine production in response to C. albicans and S. aureus. Pan-inhibitors lower overall cytokine production, whereas specific inhibitors confer a selective effect. Entinostat and RGFP966 are promising therapeutic candidates to treat STAT-1 GOF due to their capacity to restore IL-22 production and decrease STAT-1 phosphorylation; however, their inhibition of innate cytokines poses a possible risk to secondary infections.

Pitfalls in cytokine measurements - Plasma TGF-β1 in chronic fatigue syndrome

BACKGROUND

Serum TGF-β1 concentrations are reported to be elevated in chronic fatigue syndrome (CFS). However, measurement of circulating cytokines is a complex procedure and control of pre-analytical procedures is essential. The objective of the current study was to measure circulating TGF-β1 concentrations in CFS patients compared to healthy controls, taking into account differences in pre-analytical procedures.

METHODS

Two cohorts of female CFS patients were included. In both studies patients were asked to bring a healthy, age-matched control. At baseline, TGF-β1 levels were measured in plasma and additionally P-selectin, a marker of platelet activity, was determined in a subgroup of participants.

RESULTS

50 patients and 48 controls were included in cohort I, and 90 patients and 29 controls in cohort II. Within the cohorts there were no differences in TGF-β1 concentrations. However, between the cohorts there was a large discrepancy, which appeared to be caused by differences in g-force of the centrifuges used. The lower g-force used in cohort II (1361 g) caused more platelet activation, reflected by higher p-selectin concentrations, compared to cohort I (p < 0.0001), which was confirmed in a second independent experiment. There was a correlation between TGF-β1 and p-selectin concentrations (r 0.79, p < 0.0001).

CONCLUSION

These results demonstrate that control of pre-analytical procedures is an essential aspect when measuring circulating cytokines. No evidence for enhanced TGF-β1 in patients with CFS was found.

Risk of infections in patients with gout: a population-based cohort study

To investigate the risk of various types of infections (pneumonia and urinary tract infection (UTI)), and infection-related mortality in patients with gout compared with population-based controls. A retrospective cohort study was conducted using data from the UK Clinical Practice Research Datalink (CPRD). All patients with a first diagnosis of gout and aged >40 years between January 1987-July 2014, were included and matched with up to two controls. Time-varying Cox proportional hazards models were used to estimate the risk of infections and mortality. 131,565 patients and 252,763 controls (mean age: 64 years, 74% males, mean follow-up of 6.7 years) were included in the full cohort. After full statistical adjustment, the risk of pneumonia was increased (adj. HR 1.27, 95% CI 1.18 to 1.36), while the risk of UTI (adj. HR 0.99, 95% CI 0.97 to 1.01) was similar in patients compared to controls. No differences between patients and controls were observed for infection-related mortality due to pneumonia (adj. HR 1.03, 95% CI 0.93 to 1.14) or UTI (adj. HR 1.16, 95% CI 0.98 to 1.37). In conclusion, patients with gout did not have decreased risks of pneumonia, UTI or infection-related mortality compared to population-based controls.

Involvement of matrix metalloproteinases in chronic Q fever

OBJECTIVES

Chronic Q fever is a persistent infection with the intracellular Gram-negative bacterium Coxiella burnetii, which can lead to complications of infected aneurysms. Matrix metalloproteinases (MMPs) cleave extracellular matrix and are involved in infections as well as aneurysms. We aimed to study the role of MMPs in the pathogenesis of chronic Q fever.

METHODS

We investigated gene expression of MMPs through microarray analysis and MMP production with ELISA in C. burnetii-stimulated peripheral blood mononuclear cells (PBMCs) of patients with chronic Q fever and healthy controls. Twenty single nucleotide polymorphisms (SNPs) of MMP and tissue inhibitor of MMP genes were genotyped in 139 patients with chronic Q fever and 220 controls with similar cardiovascular co-morbidity. Additionally, circulating MMPs levels in patients with chronic Q fever were compared with those in cardiovascular controls with and without a history of past Q fever.

RESULTS

In healthy controls, the MMP pathway involving four genes (MMP1, MMP7, MMP10, MMP19) was significantly up-regulated in C. burnetii-stimulated but not in Escherichia coli lipopolysaccharide -stimulated PBMCs. Coxiella burnetii induced MMP-1 and MMP-9 production in PBMCs of healthy individuals (both p<0.001), individuals with past Q fever (p<0.05, p<0.01, respectively) and of patients with chronic Q fever (both p<0.001). SNPs in MMP7 (rs11568810) (p<0.05) and MMP9 (rs17576) (p<0.05) were more common in patients with chronic Q fever. Circulating MMP-7 serum levels were higher in patients with chronic Q fever (median 33.5 ng/mL, interquartile range 22.3-45.7 ng/mL) than controls (20.6 ng/mL, 15.9-33.8 ng/mL).

CONCLUSION

Coxiella burnetii-induced MMP production may contribute to the development of chronic Q fever.

Synovial macrophages promote TGF-β signaling and protect against influx of S100A8/S100A9-producing cells after intra-articular injections of oxidized low-density lipoproteins

OBJECTIVE

Low-density lipoproteins (LDL) in inflamed synovium is oxidized and taken-up by synoviocytes. In this study, we investigate whether direct injection of oxidized LDL (oxLDL) into a normal murine knee joint induces joint pathology and whether synovial macrophages are involved in that process.

DESIGN

Synovium was obtained from end-stage osteoarthritis (OA) patients in order to analyze LDL-uptake. Murine knee joints were injected five consecutive days with oxLDL, LDL, or vehicle (phosphate buffered saline (PBS)). This procedure was repeated in mice depleted of synovial macrophages by intra-articular injection of clodronate liposomes 7 days prior to the consecutive injections. Joint pathology was investigated by immunohistochemistry, flow cytometry (FCM) and synovial RNA expression and protein production.

RESULTS

Synovial tissue of OA patients showed extensive accumulation of apolipoprotein B. Multiple injections of oxLDL in murine knee joints significantly increased TGF-β activity in synovial wash-outs, but did not induce catabolic or inflammatory processes. In contrast, repeated injections of oxLDL in macrophage-depleted knee joints led to increased synovial thickening in combination with significantly upregulated protein and RNA levels of CCL2 and CCL3. FCM-analyses revealed increased presence of monocytes and neutrophils in the synovium, which was confirmed by immunohistochemistry. Also protein levels of S100A8/A9 were significantly increased in synovial wash-outs of oxLDL-injected joints, as was expression of aggrecanase-induced neo-epitopes. Interestingly, no raise in TGF-β concentrations was measured in macrophage-depleted joints.

CONCLUSIONS

OxLDL can affect joint pathology, since synovial macrophages promote anabolic processes after oxLDL injections. In absence of synovial macrophages, however, oxLDL induces production of pro-inflammatory mediators and aggrecanase activity combined with increased influx of monocytes and neutrophils.

Association of a variable number tandem repeat in the NLRP3 gene in women with susceptibility to RVVC

Vaginal infections with Candida spp. frequently occur in women of childbearing age. A small proportion of these women experience recurrent vulvovaginal candidosis (RVVC), which is characterized by at least three episodes of infection in one year. In addition to known risk factors such as antibiotics, diabetes, or pregnancy, host genetic variation and inflammatory pathways such as the IL-1/Th17 axis have been reported to play a substantial role in the pathogenesis of RVVC. In this study, we assessed a variable number tandem repeat (VNTR) polymorphism in the NLRP3 gene that encodes a component of the inflammasome, processing the proinflammatory cytokines IL-1β and IL-18. A total of 270 RVVC patients and 583 healthy controls were analyzed, and increased diseases susceptibility was associated with the presence of the 12/9 genotype. Furthermore, functional studies demonstrate that IL-1β production at the vaginal surface is higher in RVVC patients bearing the 12/9 genotype compared to controls, whereas IL-1Ra levels were decreased and IL-18 levels remained unchanged. These findings suggest that IL-1β-mediated hyperinflammation conveyed by the NLRP3 gene plays a causal role in the pathogenesis of RVVC and may identify this pathway as a potential therapeutic target in the disease.

Pattern recognition pathways leading to a Th2 cytokine bias in allergic bronchopulmonary aspergillosis patients

BACKGROUND

Allergic bronchopulmonary aspergillosis (ABPA) is characterised by an exaggerated Th2 response to Aspergillus fumigatus, but the immunological pathways responsible for this effect are unknown.

OBJECTIVE

The aim of this study was to decipher the pattern recognition receptors (PRRs) and cytokines involved in the Aspergillus-specific Th2 response and to study Aspergillus-induced responses in healthy controls and ABPA patients.

METHODS

Peripheral blood mononuclear cells (PBMCs) were stimulated with heat-killed Aspergillus conidia, various other pathogens, or PRR ligands. PRRs and cytokine pathways were blocked with PRR-blocking reagents, anti-TNF (Etanercept or Adalimumab), IL-1Ra (Anakinra) or IFNγ (IFN-gamma). ELISA and FACS were used to analyse cytokine responses.

RESULTS

Aspergillus was the only pathogen that stimulated the Th2 cytokines IL-5 and IL-13, while Gram-negative bacteria, Gram-positive bacteria, Candida albicans, chitin, β-glucan or Toll-like receptor (TLR) ligands did not. Depletion of CD4(+) cells abolished IL-13 production. Blocking complement receptor 3 (CR3) significantly reduced IL-5 and IL-13, while blocking TLR2, TLR4 or dectin-1 had no effect. ABPA patients displayed increased Aspergillus-induced IL-5 and IL-13 and decreased IFNγ production compared with healthy controls. All biological agents tested showed the capability to inhibit Th2 responses, but also decreased Aspergillus-induced IFNγ.

CONCLUSIONS AND CLINICAL RELEVANCE

Aspergillus conidia are unique in triggering Th2 responses in human PBMCs, through a CR3-dependent pathway. ABPA patients display a significantly increased Aspergillus-induced Th2/Th1 ratio that can be modulated by biologicals. These data provide a rationale to explore IFNγ therapy in ABPA as a corticosteroid-sparing treatment option, by dampening Th2 responses and supplementing the IFNγ deficiency at the same time.

Defective trained immunity in patients with STAT-1-dependent chronic mucocutaneaous candidiasis

Patients with signal transducer and activator of transcription-1 (STAT1)-dependent chronic mucocutaneous candidiasis (CMC) and patients with STAT3-dependent hyper-immunoglobulin (Ig)E syndrome (HIES) display defects in T helper type 17 (Th17) cytokine production capacity. Despite this similar immune defect in Th17 function, they show important differences in the type of infections to which they are susceptible. Recently, our group reported differential regulation of STAT-1 and STAT-3 transcription factors during epigenetic reprogramming of trained immunity, an important host defence mechanism based on innate immune memory. We therefore hypothesized that STAT1 and STAT3 defects have different effects on trained immunity, and this may partly explain the differences between CMC and HIES regarding the susceptibility to infections. Indeed, while trained immunity was normally induced in cells isolated from patients with HIES, the induction of innate training was defective in CMC patients. This defect was specific for training with Candida albicans, the main pathogen encountered in CMC, and it involved a type II interferon-dependent mechanism. These findings describe the role of STAT-1 for the induction of trained immunity, and may contribute to the understanding of the differences in susceptibility to infection between CMC and HIES patients. This study could also provide directions for personalized immunotherapy in patients suffering from these immunodeficiencies.

Autophagy is redundant for the host defense against systemic Candida albicans infections

Autophagy has been demonstrated to play an important role in the immunity against intracellular pathogens, but very little is known about its role in the host defense against fungal pathogens such as Candida albicans. Therefore, the role of autophagy for the host defense against C. albicans was assessed by complementary approaches using mice defective in autophagy, as well as immunological and genetic studies in humans. Although C. albicans induced LC3-II formation in macrophages, myeloid cell-specific ATG7(-/-) mice with defects in autophagy did not display an increased susceptibility to disseminated candidiasis. In in vitro experiments in human blood mononuclear cells, blocking autophagy modulated cytokine production induced by lipopolysaccharide, but not by C. albicans. Furthermore, autophagy modulation in human monocytes did not influence the phagocytosis and killing of C. albicans. Finally, 18 single-nucleotide polymorphisms in 13 autophagy genes were not associated with susceptibility to candidemia or clinical outcome of disease in a large cohort of patients, and there was no correlation between these genetic variants and cytokine production in either candidemia patients or healthy controls. Based on these complementary in vitro and in vivo studies, it can be concluded that autophagy is redundant for the host response against systemic infections with C. albicans.

Autophagy activity is up-regulated in adipose tissue of obese individuals and modulates proinflammatory cytokine expression

Autophagy, an evolutionary conserved process aimed at recycling damaged organelles and protein aggregates in the cell, also modulates proinflammatory cytokine production in peripheral blood mononuclear cells. Because adipose tissue inflammation accompanied by elevated levels of proinflammatory cytokines is characteristic for the development of obesity, we hypothesized that modulation of autophagy alters adipose tissue inflammatory gene expression and secretion. We tested our hypothesis using ex vivo and in vivo studies of human and mouse adipose tissue. Levels of the autophagy marker LC3 were elevated in sc adipose tissue of obese vs. lean human subjects and positively correlated to both systemic insulin resistance and morphological characteristics of adipose tissue inflammation. Similarly, autophagic activity levels were increased in adipose tissue of obese and insulin resistant animals as compared with lean mice. Inhibition of autophagy by 3-methylalanine in human and mouse adipose tissue explants led to a significant increase in IL-1β, IL-6, and IL-8 mRNA expression and protein secretion. Noticeably, the enhancement in IL-1β, IL-6, and keratinocyte-derived chemoattractant (KC) by inhibition of autophagy was more robust in the presence of obesity. Similar results were obtained by blocking autophagy using small interfering RNA targeted to ATG7 in human Simpson-Golabi-Behmel syndrome adipocytes. Our results demonstrate that autophagy activity is up-regulated in the adipose tissue of obese individuals and inhibition of autophagy enhances proinflammatory gene expression both in adipocytes and adipose tissue explants. Autophagy may function to dampen inflammatory gene expression and thereby limit excessive inflammation in adipose tissue during obesity.

Oxidized LDL enhances pro-inflammatory responses of alternatively activated M2 macrophages: a crucial role for Krüppel-like factor 2

OBJECTIVE

Macrophages are key players in atherogenesis because of their properties to form foam cells that produce a large variety of pro-inflammatory mediators. We addressed the potency of phenotypic different macrophages to accumulate oxidized LDL.

METHODS AND RESULTS

Surprisingly, anti-inflammatory M2 macrophages but not pro-inflammatory M1 macrophages rapidly accumulated oxidized LDL. Simultaneously, expression of Krüppel-like factor 2, a nuclear transcription factor known to suppress inflammation in endothelial cells and monocytes, decreased and the functional phenotype of M2 macrophages shifted towards a pro-inflammatory profile, characterized by higher production of IL-6, IL-8 and MCP-1 and lower expression of IL-10 upon stimulation with LPS. In contrast, Krüppel-like factor 2 expression and the phenotype of M1 macrophages remained largely unchanged upon oxidized LDL exposure. Downregulation of Krüppel-like factor 2 expression of M2 macrophages using siRNA technology led to a significant increase of LPS-induced MCP-1 secretion.

CONCLUSIONS

We show that (1) anti-inflammatory M2 macrophages are more susceptible to foam cell formation than pro-inflammatory M1 macrophages, (2) exposure to oxidized LDL renders M2 macrophages pro-inflammatory, and (3) Krüppel-like factor 2 is involved in the enhanced secretion of MCP-1 by M2 macrophages loaded with oxidized LDL. The phenotype switch of M2 macrophages from an anti- to a pro-inflammatory profile may play an important role in pathogenesis of atherosclerosis, and could represent a novel therapeutic target.

Chronic yersiniosis due to defects in the TLR5 and NOD2 recognition pathways

Infection with Yersinia enterocolitica leads to a self-limiting disease, but in a small number of cases a protracted course can develop. The host genetic factors contributing to the advancement of the disease to the chronic phase are not known. We describe a patient suffering from an abdominal inflammatory mass due to chronic yersiniosis. Functional assays revealed defects in the recognition of flagellin by Toll-like receptor 5 (TLR5) and of muramyl dipeptide by NOD2, leading to a defective inflammatory response to Yersinia enterocolitica. Genetic sequencing showed that the patient was compound heterozygous for five different mutations in TLR5, while being homozygous for the 3020insC NOD2 mutation. In conclusion, we describe a patient in whom specific defects in the TLR5 and NOD2 recognition pathways led to chronic yersiniosis.

von Willebrand factor activation, granzyme-B and thrombocytopenia in meningococcal disease

SUMMARY BACKGROUND

During invasive meningococcal disease, severe thrombocytopenia is strongly associated with a poor outcome.

OBJECTIVES

In order to elucidate the pathophysiological mechanism behind the development of thrombocytopenia, we studied the role of von Willebrand factor (VWF) in meningococcal disease.

PATIENTS/METHODS

Thirty-two children with severe meningococcal disease admitted to our university hospital were included in this study. VWF and related parameters were measured and results were correlated with the development of shock and thrombocytopenia.

RESULTS

At admission, all patients had increased levels of (active) VWF and VWF propeptide. The highest VWF propeptide levels were observed in patients with shock, indicating acute endothelial activation. Although VWF propeptide levels in patients with shock, with or without thrombocytopenia, were similar, increased active VWF was significantly lower in patients with thrombocytopenia as compared with patients without thrombocytopenia. ADAMTS13 was moderately decreased. However, the VWF multimeric pattern was minimally increased. We assume that these findings are explained by VWF consumption and perhaps by granzyme B (GrB). In vitro experiments showed that GrB is able to cleave VWF multimers in plasma, whereas GrB was high in patients with shock, who developed thrombocytopenia.

CONCLUSIONS

Our results demonstrate that consumption of VWF, derived from endothelial cells, could be a key feature of meningococcal disease and primary to the development of thrombocytopenia during shock.

The natural soluble form of IL-18 receptor beta exacerbates collagen-induced arthritis via modulation of T-cell immune responses

OBJECTIVE

IL-18 is a pluripotent cytokine that has been implicated in the development of rheumatoid arthritis. A soluble form of the IL-18 receptor accessory protein (sIL-18Rbeta) with unknown function has recently been identified. This study examined the ability of sIL-18Rbeta to inhibit IL-18 biological activities and to modulate immune responses during collagen-induced arthritis (CIA).

METHODS

Adenoviruses encoding sIL-18Rbeta were administered intravenously in type II collagen-immunised DBA/1 mice. Humoral responses were analysed by determining anti-bovine collagen type II (BCII) antibody levels by ELISA. Cytokine production by splenic T cells and cytokine levels in serum were measured by Luminex multi-analyte technology. CD4(+)CD25(+)Foxp3(+) regulatory T cells (Treg) were measured by flow cytometry.

RESULTS

Intravenous delivery of Ad5.sIL-18Rbeta in collagen-immunised mice led to enhanced transgene expression in splenic antigen-presenting cells (APC). A co-culture of these sIL-18Rbeta-transduced APC with purified splenic CD3(+) T cells led to a marked inhibition of IL-18-induced IFNgamma, IL-4 and IL-17 production by CD3(+) T cells. Remarkably, systemic treatment with Ad5.sIL-18Rbeta caused an exacerbation of arthritis, and histological evaluation of knee joints showed increased cartilage and bone erosion. No significant differences were observed in anti-BCII antibodies, but the aggravation was accompanied by decreased IFNgamma (-30%) and IL-4 (-44%) and increased IL-17 (+84%) production by splenic CD3(+) T cells. In addition, reduced circulating levels of CD4(+)CD25(+)Foxp3(+) Treg and anti-inflammatory IL-10 were shown.

CONCLUSION

This study identifies sIL-18Rbeta as a novel IL-18 inhibitor, which promotes CIA after intravenous overexpression by affecting Treg levels and supporting a T helper type 17 response.

Milder clinical hyperimmunoglobulin E syndrome phenotype is associated with partial interleukin-17 deficiency

Mutations in the signal transducer and activator of transcription 3 (STAT3) were reported to cause hyperimmunoglobulin E syndrome (HIES). The present study investigates T helper type 17 (Th17) responses triggered by the relevant stimuli Staphylococcus aureus and Candidia albicans in five 'classical' HIES patients, and a family with three patients who all had a milder HIES phenotype. We demonstrate that patients with various forms of HIES have different defects in their Th17 response to S. aureus and C. albicans, and this is in line with the clinical features of the disease. Interestingly, a partial deficiency of interleukin (IL)-17 production, even when associated with STAT3 mutations, leads to a milder clinical phenotype. We also observed defective Th17 responses in patients with the 'classical' presentation of the disease but without STAT3 mutations. These data demonstrate that defective IL-17 production in response to specific pathogens can differ between patients with HIES and that the extent of the defective Th17 response determines their clinical phenotype.

Type I interferons might form the link between Toll-like receptor (TLR) 3/7 and TLR4-mediated synovial inflammation in rheumatoid arthritis (RA)

BACKGROUND

Rheumatoid arthritis (RA) has been associated with an increased risk of infections, but the underlying pathways have not yet been identified. Toll-like receptors (TLR) probably play a role in synovial inflammation and may also contribute to the understanding of the role of infections in RA.

OBJECTIVES

To investigate if the synovial expression of TLR3 and TLR7 in RA correlates with that of inflammatory cytokines, and to assess whether this has functional consequences for local cytokine production and to study potential links between the TLR3/7 axis and TLR4 in RA synovium.

METHODS

Immunohistochemistry was used to study the expression of TLR3, TLR7, interferon alpha (IFNalpha), tumour necrosis factor alpha (TNFalpha) and interleukins IL1beta, IL12, IL17 and IL18 in RA synovium obtained by arthroscopy from 34 patients with RA. Monocytes, monocyte-derived dendritic cells (MoDCs) and RA synovial fibroblasts were stimulated via TLR3 (poly-IC) and TLR7 (loxorubin), after which IL1beta, IL6 and TNFalpha were measured by Luminex bead array technology. Following preincubation with IFNalpha, IL1beta and IL18, TLR3 and TLR7 mRNA expression was assessed using real-time PCR. Cytokine production after preincubation with IFNalpha and subsequent TLR stimulation was measured.

RESULTS

Synovial TLR3/7 expression was co-expressed with IFNalpha, IL1beta and IL18, but not with TNFalpha, IL12 and IL17. Stimulation of TLR3/TLR7 on monocytes, MoDCs or synovial fibroblasts led to secretion of type I IFN but no biologically active IL1beta or IL18 could be detected. Type I IFNalpha increased TLR3/7 mRNA expression whereas IL1beta and IL18 did not. In spite of the fact that the mRNA level of TLR4 remained unchanged, IFNalpha enhanced the response to TLR4 agonists, a phenomenon that was clearly more marked in patients with RA.

CONCLUSION

Type I interferons are highly co-expressed with TLR3/TLR7 in RA synovium. They enhance TLR3/TLR7-mediated cytokine production and also TLR4-mediated responses.

Combined blockade of granulocyte-macrophage colony stimulating factor and interleukin 17 pathways potently suppresses chronic destructive arthritis in a tumour necrosis factor alpha-independent mouse model

OBJECTIVE

A pathogenic role for granulocyte-macrophage colony stimulating factor (GM-CSF) and interleukin (IL)17 in rheumatoid arthritis (RA) has been suggested. In previously published work, the therapeutic potentials of GM-CSF and IL17 blockade in arthritis have been described. In the present study, the simultaneous blockade of both pathways in a mouse model for chronic arthritis was investigated to identify whether this double blockade provides a superior therapeutic efficacy.

METHODS

A chronic relapsing arthritis was induced in C57Bl/6 wild type (WT) and C57Bl/6 genetically deficient for IL17 receptor (IL17R knockout (KO)) mice by intra-articular injection of Streptococcal cell wall (SCW) fragments into knees on days 0, 7, 14 and 21. Treatments (intraperitoneal) were given weekly starting on day 14. Animals were analysed for inflammation, joint damage and a range of inflammatory mediators.

RESULTS

Joint swelling and cartilage damage were significantly reduced in the IL17R KO mice and in WT mice receiving anti-GM-CSF neutralising mAb 22E9 compared to isotype control antibodies. The therapeutic effect was significantly more pronounced in mice where IL17 and GM-CSF pathways were inhibited (eg, IL17R KO mice treated with 22E9 mAb). Tumour necrosis factor (TNF)alpha blockade had essentially no effect.

CONCLUSION

Our data further support the therapeutic potentials of GM-CSF and IL17 blockade in a RA model that is no longer responsive to an established TNFalpha antagonist, moreover, our results suggest that concomitant inhibition of both pathways may provide the basis for a highly effective treatment of chronic RA in patients that are resistant to treatment by TNFalpha inhibitors.

Application of a disease-regulated promoter is a safer mode of local IL-4 gene therapy for arthritis

The application of disease-regulated promoters in local gene therapy for rheumatoid arthritis potentiates the development of a sophisticated treatment that relies on a restricted and fine-tuned supply of biologicals. Although several studies have investigated regulated promoters for achieving effective transgene expression during arthritis, none have explored their potential for minimizing deleterious effects arising from constitutive overexpression of transgenes under naive conditions. Using naive and collagen-induced arthritic mice, we examined the applicability of a hybrid interleukin-1 enhancer/interleukin-6 proximal promoter for achieving efficacious murine interleukin-4 gene therapy under arthritic conditions, while minimizing interleukin-4-induced inflammation under naive conditions. We found strong upregulation of transgene expression in virally transduced knee joints under arthritic conditions compared to levels in naive animals. Besides its responsiveness, the promoter strength proved sufficient for generating therapeutically efficacious levels interleukin-4, as demonstrated by the successful protection against cartilage erosion in collagen-induced arthritis. Most importantly, promoter-mediated restriction of the potent chemotactic interleukin-4 in naive animals strongly reduced the amounts of inflammatory cell influx. This study suggests the suitability of the interleukin-1 enhancer/interleukin-6 proximal promoter for the development of a local gene therapy strategy for rheumatoid arthritis that requires fine-tuned and restricted expression of transgenes with a pleiotrophic nature.

Increased voluntary exercise in mice deficient for tumour necrosis factor-alpha and lymphotoxin-alpha

BACKGROUND

The endogenous mediators playing a role in the sensing of fatigue and cessation of exercise are yet to be characterized. We hypothesized that proinflammatory cytokines, in particular tumour necrosis factor-alpha (TNFalpha) and lymphotoxin-alpha (LT) transmit signals leading to fatigue.

MATERIALS AND METHODS

Mice were placed in a cage with a freely rotating exercise wheel and allowed to adapt for 24 h. The running distance was measured for two additional periods of 24 h. The effects of the administration of intravenous anti-TNF antibodies, intracerebral recombinant TNF, or intravenous lipopolysaccharide (LPS) were also determined.

RESULTS

Compared to normal littermates, the voluntary daily running distance was 1.8-fold greater in mice with a disruption of the gene for TNFalpha, and 3-fold greater in mice with a gene disruption for both TNFalpha and LT. Intravenous administration of a monoclonal antibody against murine TNFalpha did not affect the running distance of wild-type mice, whereas administration of TNF intracerebrally reduced by 4-fold the voluntary running distance of the animals. This demonstrates that fatigue is mediated by TNFalpha expressed in the central nervous system (CNS) and not by increased peripheral TNFalpha concentrations. TNFalpha and LT are strong inducers of prostaglandins, but mice with disrupted prostaglandin or prostacyclin receptors exhibited running distances not significantly different from their wild-type littermates. Thus, signalling molecules other than prostaglandins mediate the effect of TNFalpha and LT on exercise capacity.

CONCLUSIONS

Our finding that exercise capacity is controlled by TNFalpha is the first to define the endogenous mediators of fatigue, and may have important implications for diseases with impaired exercise tolerance.

Potential new targets in arthritis therapy: interleukin (IL)-17 and its relation to tumour necrosis factor and IL-1 in experimental arthritis

Rheumatoid arthritis (RA) is a systemic autoimmune disease characterised by chronic joint inflammation and destruction. Interleukin (IL)-17 is a T cell cytokine expressed in the synovium and synovial fluid of patients with RA. IL-17 is a potent inducer of various cytokines such as tumour necrosis factor (TNF) and IL-1. IL-17 has been shown to have additive or even synergistic effects with TNF and IL-1 during the induction of cytokine expression and joint damage in vitro and in vivo. TNFalpha and IL-1 are considered powerful targets in the treatment of RA because of their leading role in driving the enhanced production of cytokines, chemokines, and degradative enzymes. Besides anti-TNF and anti-IL-1 therapies, whose clinical efficacy is now established, new targets have been proposed for RA which is not responding to conventional treatments. This paper discusses the role of IL-17 in experimental arthritis and its interrelationship with TNF and IL-1, currently the most targeted cytokines in the treatment of RA. IL-17 is involved in both initiation and progression of murine experimental arthritis. Studies have shown that IL-17 not only synergises with TNF, but also enhances inflammation and destruction independent of IL-1 and TNF. On the basis of these studies, the authors propose IL-17 as an interesting additional target in the treatment of RA.

GM-CSF neutralisation suppresses inflammation and protects cartilage in acute streptococcal cell wall arthritis of mice

OBJECTIVE

The pathogenic involvement of granulocyte-macrophage colony-stimulating factor (GM-CSF) in arthritis has been put forward. We have investigated the therapeutic effect of GM-CSF neutralisation in the streptococcal cell wall (SCW) arthritis model in mice. In this model, the pathogenic contribution of tumour necrosis factor (TNF)alpha is minor and is expressed only on joint swelling, whereas cartilage proteoglycan depletion is independent of this cytokine.

METHODS

Acute monarthritis was induced by injection of SCW bacterial extracts to mouse knees. Treatments (mAb 22E9 at 300, 100, 30 microg; or Enbrel 300 microg) were given twice intraperitoneally 2 h before and 3 days after disease induction. Swelling was assessed by (99m)Tc uptake into knees on days 1 and 2. Local cytokine levels were determined in patellae washouts on day one. Proteoglycan loss from cartilage was scored on histological sections at termination on day four.

RESULTS

Treatment with anti-GM-CSF mAb 22E9 showed a dose-related efficacy by decreasing swelling that was significant at the 300 and 100 microg doses in comparison to isotype control, and comparable to dexamethasone (5 mg/ml). Proteoglycan loss from cartilage was also significantly reduced by mAb 22E9 300 microg (p=0.001). This reduced proteoglycan loss observed after GM-CSF neutralisation was not seen after TNFalpha-blockade with Enbrel. Similarly, levels of interleukin 1beta in joints were reduced after treatment with 22E9 mAb (p=0.003) but not in mice receiving Enbrel.

CONCLUSIONS

Our findings show a pathogenic role for GM-CSF in this arthritis model, support the therapeutic potential of neutralising this cytokine, and may indicate therapeutic activity of an anti-GM-CSF mAb in TNFalpha-independent disease situations.

High-resolution multipinhole single-photon-emission computed tomography in experimental and human arthritis

OBJECTIVE

To image inflammatory arthritic lesions in experimental arthritis and in patients with arthritis, using a newly developed high-resolution multipinhole single-photon-emission computed tomography (MPH-SPECT) technique.

METHODS

Six interleukin-1 receptor antagonist-deficient mice with arthritis of the front and back paws and 2 control BALB/c mice were imaged with MPH-SPECT and scored macroscopically for arthritis. SPECT imaging was performed with a conventional gamma camera upgraded with a pyramidal lead collimator affixed with MPH apertures. All images were reconstructed, and uptake in the paws was quantified in counts/weight and injected activity. To transfer the imaging technique to humans we examined the clinically dominant hand of 6 individuals (3 with established rheumatoid arthritis [RA], 1 with early RA, 1 with osteoarthritis, and 1 healthy control).

RESULTS

MPH-SPECT images were high-resolution 3-dimensional tomographic images, which allowed exact localization and quantifiable observation of increased bone metabolism. MPH-SPECT counts of inflamed joints in mice correlated with macroscopic scoring and histologic joint analysis postmortem. In humans, MPH-SPECT images depicted a detailed visualization of tracer accumulation in bony structures of hand and finger joints, and were also capable of imaging increased bone metabolism that had appeared normal with other imaging modalities, e.g., magnetic resonance imaging.

CONCLUSION

The MPH-SPECT technique represents a new diagnostic tool in the detection of bone pathology in small-animal arthritis research. Compared with macroscopic scoring, this new method provides a more objective and higher-precision quantifiable measurement of bone reaction, allowing visualization of inflammatory processes of the whole skeleton in vivo. These results suggest that MPH-SPECT may be useful as a diagnostic instrument for monitoring experimental arthritis, with further potential for use in human studies of RA.

A novel role for suppressor of cytokine signaling 3 in cartilage destruction via induction of chondrocyte desensitization toward insulin-like growth factor

OBJECTIVE

An important mechanism contributing to cartilage destruction in arthritis is chondrocyte desensitization toward its main anabolic factor, insulin-like growth factor 1 (IGF-1). In this study, we sought to determine the role of suppressor of cytokine signaling 3 (SOCS-3) in the induction of IGF-1 desensitization of murine chondrocytes.

METHODS

Chondrocyte responsiveness to IGF-1 was assessed by 35S-sulfate incorporation into proteoglycans (PGs), via aggrecan messenger RNA expression, using quantitative real-time polymerase chain reaction or insulin receptor substrate 1 (IRS-1) tyrosine phosphorylation (Western blot analysis). IGF-1 desensitization of patellar chondrocytes was studied in zymosan-induced arthritis. IGF-1 desensitization was induced in patellar cartilage explants or the H4 chondrocyte cell line, exposed to interleukin-1alpha (IL-1alpha). SOCS-3 protein expression was assessed by immunohistochemistry or by Western blot analysis of protein extracts. The role of SOCS-3 in IGF-1 signaling was elucidated by adenoviral overexpression.

RESULTS

Exposure of murine articular cartilage to IL-1 caused a significant decrease in IGF-1-induced PG synthesis. This effect also occurred in inducible nitric oxide synthase-knockout mice, revealing the involvement of a secondary IL-1-induced factor other than nitric oxide. We showed that IL-1 significantly up-regulated SOCS-3 transcription and protein synthesis in H4 chondrocytes. In contrast, IL-18 was unable to induce SOCS-3 expression and failed to induce chondrocyte IGF-1 desensitization. Histologic analysis of samples from arthritic knee joints revealed high expression of SOCS-3 in chondrocytes. Through adenoviral overexpression of SOCS-3, we obtained direct evidence that SOCS-3 inhibits IGF-1-mediated cell signaling, since IRS-1 phosphorylation was reduced.

CONCLUSION

This study demonstrates that IL-1-induced SOCS-3 expression is a novel mechanism of IGF-1 desensitization in chondrocytes; in conjunction with nitric oxide it can contribute to cartilage damage during arthritis.

The expression of toll-like receptors 3 and 7 in rheumatoid arthritis synovium is increased and costimulation of toll-like receptors 3, 4, and 7/8 results in synergistic cytokine production by dendritic cells

OBJECTIVE

To evaluate the expression of Toll-like receptors (TLRs) 3 and 7 in synovium and to study potential differences in the maturation and cytokine production mediated by TLR-2, TLR-3, TLR-4, and TLR-7/8 by dendritic cells (DCs) from rheumatoid arthritis (RA) patients and DCs from healthy controls.

METHODS

Synovial expression of TLR-3 and TLR-7 in RA was studied using immunohistochemistry. Monocyte-derived DCs from RA patients and healthy controls were cultured for 6 days and subsequently stimulated for 48 hours via TLR-mediated pathways (lipoteichoic acid, Pam(3)Cys, and fibroblast-stimulating lipopeptide 1 for TLR-2, poly[I-C] for TLR-3, lipopolysaccharide and extra domain A for TLR-4, and R848 for TLR-7/8). Phenotypic DC maturation was measured using flow cytometry. The secretion of tumor necrosis factor alpha (TNFalpha), interleukin-6 (IL-6), IL-10, and IL-12 was measured using the Bio-Plex system. Cell lines expressing TLR-2 and TLR-4 were used for the detection of TLR-2 and TLR-4 ligands in serum and synovial fluid from RA patients.

RESULTS

TLR-3 and TLR-7 were highly expressed in RA synovium. All TLR ligands elicited phenotypic DC maturation equally between DCs from RA patients and those from healthy controls. TLR-2- and TLR-4-mediated stimulation of DCs from RA patients resulted in markedly higher production of inflammatory mediators (TNFalpha and IL-6) compared with DCs from healthy controls. In contrast, upon stimulation of TLR-3 and TLR-7/8, the level of cytokine production was equal between DCs from RA patients and those from healthy controls. Remarkably, both TLR-3 and TLR-7/8 stimulation resulted in a skewed balance toward IL-12. Intriguingly, the combined stimulation of TLR-4 and TLR-3-7/8 resulted in a marked synergy with respect to the production of inflammatory mediators. As a proof of concept, TLR-4 ligands were increased in the serum and synovial fluid of RA patients.

CONCLUSION

TLRs are involved in the regulation of DC activation and cytokine production. We hypothesize that various TLR ligands in the joint trigger multiple TLRs simultaneously, favoring the breakthrough of tolerance in RA.