Differences in the inflammatory proteome of East African and Western European adults and associations with environmental and dietary factors

Non-communicable diseases (NCDs) are rising rapidly in urbanizing populations in sub-Saharan Africa. Assessment of inflammatory and metabolic characteristics of a urbanizing African population and the comparison with populations outside Africa could provide insight in the pathophysiology of the rapidly increasing epidemic of NCDs, including the role of environmental and dietary changes. Using a proteomic plasma profiling approach comprising 92 inflammation-related molecules, we examined differences in the inflammatory proteome in healthy Tanzanian and healthy Dutch adults. We show that healthy Tanzanians display a pro-inflammatory phenotype compared to Dutch subjects, with enhanced activity of the Wnt/β-catenin signalling pathway and higher concentrations of different metabolic regulators such as 4E-BP1 and fibroblast growth factor 21. Among the Tanzanian volunteers, food-derived metabolites were identified as an important driver of variation in inflammation-related molecules, emphasizing the potential importance of lifestyle changes. These findings endorse the importance of the current dietary transition and the inclusion of underrepresented populations in systems immunology studies.

Evolution of cytokine production capacity in ancient and modern European populations

As our ancestors migrated throughout different continents, natural selection increased the presence of alleles advantageous in the new environments. Heritable variations that alter the susceptibility to diseases vary with the historical period, the virulence of the infections, and their geographical spread. In this study we built polygenic scores for heritable traits that influence the genetic adaptation in the production of cytokines and immune-mediated disorders, including infectious, inflammatory, and autoimmune diseases, and applied them to the genomes of several ancient European populations. We observed that the advent of the Neolithic was a turning point for immune-mediated traits in Europeans, favoring those alleles linked with the development of tolerance against intracellular pathogens and promoting inflammatory responses against extracellular microbes. These evolutionary patterns are also associated with an increased presence of traits related to inflammatory and auto-immune diseases.

The neuromuscular and multisystem features of RYR1-related malignant hyperthermia and rhabdomyolysis: A study protocol

INTRODUCTION

Malignant hyperthermia (MH) and exertional rhabdomyolysis (ERM) have long been considered episodic phenotypes occurring in response to external triggers in otherwise healthy individuals with variants in RYR1. However, recent studies have demonstrated a clinical and histopathological continuum between patients with RYR1-related congenital myopathies and those with ERM or MH susceptibility. Furthermore, animal studies have shown non-neuromuscular features such as a mild bleeding disorder and an immunological gain-of-function associated with MH/ERM related RYR1 variants raising important questions for further research. Awareness of the neuromuscular disease spectrum and potential multisystem involvement in RYR1-related MH and ERM is essential to optimize the diagnostic work-up, improve counselling and and future treatment strategies for patients affected by these conditions. This study will examine in detail the nature and severity of continuous disease manifestations and their effect on daily life in patients with RYR1-related MH and ERM.

METHODS

The study protocol consists of four parts; an online questionnaire study, a clinical observational study, muscle imaging, and specific immunological studies. Patients with RYR1-related MH susceptibility and ERM will be included. The imaging, immunological and clinical studies will have a cross-sectional design, while the questionnaire study will be performed three times during a year to assess disease impact, daily living activities, fatigue and pain. The imaging study consists of muscle ultrasound and whole-body magnetic resonance imaging studies. For the immunological studies, peripheral mononuclear blood cells will be isolated for in vitro stimulation with toll-like receptor ligands, to examine the role of the immune system in the pathophysiology of RYR1-related MH and ERM.

DISCUSSION

This study will increase knowledge of the full spectrum of neuromuscular and multisystem features of RYR1-related MH and ERM and will establish a well-characterized baseline cohort for future studies on RYR1-related disorders. The results of this study are expected to improve recognition of RYR1-related symptoms, counselling and a more personalized approach to patients affected by these conditions. Furthermore, results will create new insights in the role of the immune system in the pathophysiology of MH and ERM.

TRIAL REGISTRATION

This study was pre-registered at ClinicalTrials.gov (ID: NCT04610619).

Trained immunity as a novel approach against COVID-19 with a focus on Bacillus Calmette-Guérin vaccine: mechanisms, challenges and perspectives

COVID-19 is a severe health problem in many countries and has altered day-to-day life in the whole world. This infection is caused by the SARS-CoV-2 virus, and depending on age, sex and health status of the patient, it can present with variety of clinical symptoms such as mild infection, a very severe form or even asymptomatic course of the disease. Similarly to other viruses, innate immune response plays a vital role in protection against COVID-19. However, dysregulation of innate immunity could have a significant influence on the severity of the disease. Despite various efforts, there is no effective vaccine against the disease so far. Recent data have demonstrated that the Bacillus Calmette-Guérin (BCG) vaccine could reduce disease severity and the burden of several infectious diseases in addition to targeting its primary focus tuberculosis. There is growing evidence for the concept of beneficial non-specific boosting of immune responses by BCG or other microbial compounds termed trained immunity, which may protect against COVID-19. In this manuscript, we review data on how the development of innate immune memory due to microbial compounds specifically BCG can result in protection against SARS-CoV-2 infection. We also discuss possible mechanisms, challenges and perspectives of using innate immunity as an approach to reduce COVID-19 severity.

Rare NOX3 Variants Confer Susceptibility to Agranulocytosis During Thyrostatic Treatment of Graves' Disease

Agranulocytosis is a rare and serious adverse effect of antithyroid drugs, with unknown etiology. The present study aimed to uncover genetic susceptibility and underlying mechanisms of antithyroid drug-induced agranulocytosis (ATDAC). We studied two independent families with familial Graves' disease, of which several members developed ATDAC. In addition, six sporadic ATDAC patients with Graves' disease were investigated. Whole exome sequencing analysis of affected and unaffected family members was performed to identify genetic susceptibility variants for ATDAC, followed by functional characterization of primary granulocytes from patients and unrelated healthy controls. Whole exome sequencing, cosegregation analysis, and stringent selection criteria of candidate gene variants identified NOX3 as a genetic factor related to ATDAC. Functional studies revealed increased apoptosis of methimazole-treated granulocytes from patients carrying NOX3 variants. In conclusion, genetic variants in NOX3 may confer susceptibility to antithyroid drug-induced apoptosis of granulocytes. These findings contribute to the understanding of the mechanisms underlying ATDAC.

ABCG2 polymorphisms in gout: insights into disease susceptibility and treatment approaches

As a result of the association of a common polymorphism (rs2231142, Q141K) in the ATP-binding cassette G2 (ABCG2) transporter with serum urate concentration in a genome-wide association study, it was revealed that ABCG2 is an important uric acid transporter. This review discusses the relevance of ABCG2 polymorphisms in gout, possible etiological mechanisms, and treatment approaches. The 141K ABCG2 urate-increasing variant causes instability in the nucleotide-binding domain, leading to decreased surface expression and function. Trafficking of the protein to the cell membrane is altered, and instead, there is an increased ubiquitin-mediated proteasomal degradation of the variant protein as well as sequestration into aggresomes. In humans, this leads to decreased uric acid excretion through both the kidney and the gut with the potential for a subsequent compensatory increase in renal urinary excretion. Not only does the 141K polymorphism in ABCG2 lead to hyperuricemia through renal overload and renal underexcretion, but emerging evidence indicates that it also increases the risk of acute gout in the presence of hyperuricemia, early onset of gout, tophi formation, and a poor response to allopurinol. In addition, there is some evidence that ABCG2 dysfunction may promote renal dysfunction in chronic kidney disease patients, increase systemic inflammatory responses, and decrease cellular autophagic responses to stress. These results suggest multiple benefits in restoring ABCG2 function. It has been shown that decreased ABCG2 141K surface expression and function can be restored with colchicine and other small molecule correctors. However, caution should be exercised in any application of these approaches given the role of surface ABCG2 in drug resistance.

High variability of TLR4 gene in different ethnic groups in Iran

Infectious diseases exert a constant evolutionary pressure on the innate immunity genes. TLR4, an important member of the TLR family, specifically recognizes conserved structures of various infectious pathogens. Two functional TLR4 polymorphisms, Asp299Gly and Thr399Ile, modulate innate host defense against infections, and their prevalence between various populations has been proposed to be influenced by local infectious pressures. If this assumption is true, strong local infectious pressures would lead to a homogeneous pattern of these ancient TLR4 polymorphisms in geographically-close populations, while a weak selection or genetic drift may result in a diverse pattern. We evaluated TLR4 polymorphisms in 15 ethnic groups in Iran, to assess whether infections exerted selective pressures on different haplotypes containing these variants. The Iranian subpopulations displayed a heterogeneous pattern of TLR4 polymorphisms, comprising various percentages of Asp299Gly and Thr399Ile, alone or in combination. The Iranian sample, as a whole, showed an intermediate mixed pattern when compared with commonly-found patterns in Africa, Europe, Eastern Asia and the Americas. These findings suggest a weak, or absent, selection pressure on TLR4 polymorphisms in the Middle-East that does not support the assumption of an important role of these polymorphisms in the host defense against local pathogens.

Attenuated atherosclerosis upon IL-17R signaling disruption in LDLr deficient mice

Atherosclerosis is an inflammatory disease characterized by the influx of macrophages and T cells and IL-17 may connect innate and adaptive immune responses involved in atherogenesis. We investigated the role of IL-17 receptor signaling in atherosclerosis and transplanted LDLr deficient recipient mice with IL-17R deficient bone marrow. Induction of atherosclerosis by Western-type diet induced a 46% reduction in lesion size in the aortic root and the plaque composition revealed no significant changes in collagen content and neutrophil counts, but a reduction in mast cell number and an increase in macrophage number. In addition, we observed a decrease in anti-oxLDL antibodies of the IgG class upon IL-17R BMT, while introduction of IL-17R deficient bone marrow resulted in a reduced IL-6 production and an increased IL-10 production. In conclusion, signaling via the IL-17 receptor in bone marrow derived cells enhances the process of atherosclerosis.

Therapeutic effect of neutralizing endogenous IL-18 activity in the collagen-induced model of arthritis

Two distinct IL-18 neutralizing strategies, i.e. a rabbit polyclonal anti-mouse IL-18 IgG and a recombinant human IL-18 binding protein (rhIL-18BP), were used to treat collagen-induced-arthritic DBA/1 mice after clinical onset of disease. The therapeutic efficacy of neutralizing endogenous IL-18 was assessed using different pathological parameters of disease progression. The clinical severity in mice undergoing collagen-induced arthritis was significantly reduced after treatment with both IL-18 neutralizing agents compared to placebo treated mice. Attenuation of the disease was associated with reduced cartilage erosion evident on histology. The decreased cartilage degradation was further documented by a significant reduction in the levels of circulating cartilage oligomeric matrix protein (an indicator of cartilage turnover). Both strategies efficiently slowed disease progression, but only anti-IL-18 IgG treatment significantly decreased an established synovitis. Serum levels of IL-6 were significantly reduced with both neutralizing strategies. In vitro, neutralizing IL-18 resulted in a significant inhibition of TNF-alpha, IL-6, and IFN-gamma secretion by macrophages. These results demonstrate that neutralizing endogenous IL-18 is therapeutically efficacious in the murine model of collagen-induced arthritis. IL-18 neutralizing antibody or rhIL-18BP could therefore represent new disease-modifying anti-rheumatic drugs that warrant testing in clinical trials in patients with rheumatoid arthritis.

A tropism-modified adenoviral vector increased the effectiveness of gene therapy for arthritis

Adenoviral vectors (AdV) are used for anti-inflammatory cytokine therapy in experimental arthritis. Cell entry of AdV is dependent on the initial recognition of the coxsackie-adenovirus receptor (CAR) on cells. Recently, an Arg-Gly-Asp (RGD) motif was introduced in the HI loop of the fiber knob, this enables the adenovirus to bypass CAR and mediate cell entry via RGD binding integrins. In this study, we explored the transduction efficiency of the RGD-modified adenovirus in synovium and compared the RGD-modified with the conventional adenoviral vector for their effectiveness to modulate the murine collagen-induced arthritis (CIA) model when used to overexpress mIL-1Ra in the knee joint. Twenty-four hours after intra-articular injection of 10(7) fluorescent forming units (ffu) virus, luciferase (luc) activity in Ad5LucRGD-injected joints was up to 38 times higher than in AdCMVLuc-injected joints, and in arthritic joints the transduction efficiency was up to 69 times higher for the Ad5LucRGD viruses. Transduction of the synovial lining by the RGD-modified adenovirus containing the mIL-1Ra transgene, markedly improved the inhibition of CIA compared with the conventional virus in both a prophylactic and therapeutic treatment protocol. These results show that targeting integrins with the RGD-modified AdV improved the outcome of gene therapy for arthritis.

Genetic ablation of interferon-gamma up-regulates interleukin-1beta expression and enables the elicitation of collagen-induced arthritis in a nonsusceptible mouse strain

OBJECTIVE

To determine whether the lack of interferon-gamma (IFNgamma) alters resistance to collagen-induced arthritis (CIA) in a nonsusceptible mouse strain, and if so, to identify changes in the antibody, cellular type II collagen (CII)-specific immune responses, and cytokine gene expression that might account for the altered susceptibility.

METHODS

CIA-resistant C57BL/6 and C57BL/6 IFNgamma-/- mice were immunized with bovine CII in Freund's complete adjuvant (CFA) or in CFA alone. Animals were monitored for signs of arthritis for up to 80 days; arthritis severity was assessed visually and histologically. Sera were collected at various time points after immunization for measurement of anti-CII antibody levels. T cell responses to bovine CII were assessed in proliferation assays. Cytokine messenger RNA (mRNA) expression in lymph node cells and in synovial cells from arthritic paws was measured by RNase protection assays, and levels of cytokine protein production were determined by enzyme-linked immunosorbent assay.

RESULTS

IFNgamma-/- mice developed a severe autoimmune arthritis that was dependent on immunization with CII. IFNgamma-/- mice produced significantly higher amounts of IgG1 and IgG2b antibody to the autoantigen, murine CII, compared with wild-type C57BL/6 mice and had an enhanced T cell proliferative response to bovine CII. Enhanced production of mature interleukin-1/beta (IL-1beta) protein was observed, but no significant changes in Th1 or Th2 cytokines. Although IL-6 and tumor necrosis factor alpha transcripts were clearly evident in the synovial cells from the arthritic paws of IFNgamma-/- mice, neither message was elevated to the levels measured for IL-1beta expression. Treatment of IFNgamma-/- mice with anti-IL-1beta significantly reduced the incidence and severity of the inflammation.

CONCLUSION

Endogenous IFNgamma plays a role in the regulation of IL-1beta, in this model of autoimmune arthritis.

Lethal Escherichia coli and Salmonella typhimurium endotoxemia is mediated through different pathways

Despite the differences in the molecular structure between lipopolysaccharides (LPS) isolated from Escherichia coli, Klebsiella pneumoniae or Salmonella typhimurium, the potential differences in their biological effects in vivo have not been investigated. In the present study, TNF and LT double knock-out (TNF-/-LT-/-) mice were almost as susceptible as TNF+/+LT+/+ controls to S. typhimurium LPS, but they were significantly more resistant to lethal endotoxemia induced by E. coli or K. pneumoniae LPS. The effect was not due to endotoxin-associated proteins. In the knock-out mice, this difference in lethality was accompanied by decreased interleukin-1 (IL-1) and interferon-gamma (IFN-gamma) production after challenge with E. coli LPS, whereas after S. typhimurium LPS more IL-1 and IFN-gamma were produced. In contrast, more IL-10 was produced after challenge of mice with E. coli LPS than with S. typhimurium LPS. The hypothesis that a combination of pro-inflammatory cytokines is responsible for the mortality after S. typhimurium LPS was suggested by experiments in mice deficient in IL-1beta-converting enzyme (ICE-/- mice). ICE-/-mice, lacking mature IL-1beta and IL-18, but also defective in IFN-gamma and TNF production, were completely protected against both E. coli and S. typhimurium LPS. Experiments in Toll-like receptor (TLR)-4 defective mice suggested that the difference is not due to differential activation of TLR4. In conclusion, TNF and LT play a central role in the lethality due to E. coli LPS, whereas the lethal effects of S. typhimurium LPS are mediated through mechanisms also involving other cytokines such as IFN-gamma, IL-1 and IL-18.

IL-1-independent role of IL-17 in synovial inflammation and joint destruction during collagen-induced arthritis

T cell IL-17 displays proinflammatory properties and is expressed in the synovium of patients with rheumatoid arthritis. Its contribution to the arthritic process has not been identified. Here, we show that blocking of endogenous IL-17 in the autoimmune collagen-induced arthritis model results in suppression of arthritis. Also, joint damage was significantly reduced. In contrast, overexpression of IL-17 enhanced collagen arthritis. Moreover, adenoviral IL-17 injected in the knee joint of type II collagen-immunized mice accelerated the onset and aggravated the synovial inflammation at the site. Radiographic and histologic analysis showed markedly increased joint destruction. Elevated levels of IL-1beta protein were found in synovial tissue. Intriguingly, blocking of IL-1alphabeta with neutralizing Abs had no effect on the IL-17-induced inflammation and joint damage in the knee joint, implying an IL-1 independent pathway. This direct potency of IL-17 was underscored in the unabated IL-17-induced exaggeration of bacterial cell wall-induced arthritis in IL-1beta(-/-) mice. In conclusion, this data shows that IL-17 contributes to joint destruction and identifies an IL-1-independent role of IL-17. These findings suggest IL-17 to be a novel target for the treatment of destructive arthritis and may have implications for tissue destruction in other autoimmune diseases.

Effects of treatment with a fully human anti-tumour necrosis factor alpha monoclonal antibody on the local and systemic homeostasis of interleukin 1 and TNFalpha in patients with rheumatoid arthritis

OBJECTIVES

To study the short term effects of a single dose of D2E7, a fully human anti-tumour necrosis factor (TNFalpha) monoclonal antibody (mAb), on the local and systemic homeostasis of interleukin 1beta (IL1beta) and TNFalpha in patients with rheumatoid arthritis (RA).

METHODS

All patients with RA enrolled in a phase I, single dose, placebo controlled study with D2E7 in our centre were studied. Systemic cytokine levels, acute phase reactants, and leucocyte counts were studied at days 0, 1, and 14 after the first administration of anti-TNF mAb (n=39) or placebo (n=11). The cellularity and the expression of IL1 and TNFalpha in synovial tissue were studied in knee biopsy specimens obtained at baseline and at day 14 in 25 consenting patients.

RESULTS

A single dose of anti-TNF mAb induced a rapid clinical improvement, a decrease in acute phase reaction, and increased lymphocyte counts in patients with active RA. The protein levels of IL1beta in the circulation were low and remained unchanged, but the systemic levels of IL1beta mRNA (p=0.002) and the concentrations of IL1 receptor antagonist (IL1ra) and IL6 (p=0.0001) had already dropped within 24 hours and this persisted up to day 14. Systemic levels of TNFalpha mRNA were low and remained unchanged, though total TNFalpha (free and bound) in the circulation increased after D2E7, probably reflecting the presence of TNF-antiTNF mAb complexes (p<0.005, at days 1 and 14). Both TNF receptors dropped below baseline levels at day 14 (p<0.005). Despite clinical improvement of arthritis, no consistent immunohistological changes were seen two weeks after anti-TNF administration. Endothelial staining for IL1beta tended to decrease in treated patients (p=0.06) but not in responders. The staining for IL1beta and TNFalpha in sublining layers and vessels was mutually correlated (r(s)=0.47 and 0.58 respectively, p<0.0005) and the microscopic scores for inflammation correlated with sublining TNFalpha and IL1beta scores (r(s)=0.65 and 0.54 respectively, p<0.0001), though none of these showed significant changes during the study.

CONCLUSIONS

Blocking TNFalpha in RA results in down regulation of IL1beta mRNA at the systemic level and in reduction of the endogenous antagonists for IL1 and TNF and of other cytokines related to the acute phase response, such as IL6, within days. At the synovial level, anti-TNF treatment does not modulate IL1beta and TNFalpha in the short term. The synovial expression of these cytokines does not reflect clinical response to TNF neutralisation.

An IFN-gamma-independent proinflammatory role of IL-18 in murine streptococcal cell wall arthritis

IL-18 is a member of the IL-1 family of proteins that exerts proinflammatory effects. It was formally known as IFN-gamma-inducing factor and is a pivotal cytokine for the development of Th1 responses. Apart from Th1 immune-stimulatory activity, IL-18 induces the production of proinflammatory cytokines such as TNF-alpha and IL-1 in vitro. The goal was to investigate the role of endogenous IL-18 in murine streptococcal cell wall (SCW)-induced arthritis. Furthermore, we investigated whether IL-18 neutralization had an impact on local TNF and IL-1 production. C57BL/6, BALB/c, and IFN-gamma-deficient mice were injected with 2 mg of rabbit anti-murine IL-18 Abs shortly before induction of arthritis by intra-articular injection of 25 microg of SCW fragments into the right knee joint. Suppression of joint swelling was noted on days 1 and 2 of SCW arthritis after blockade of endogenous IL-18. Analysis of local cytokine concentrations showed that IL-18, TNF-alpha, and IL-1ss levels were decreased. Severe inhibition of chondrocyte proteoglycan synthesis was seen in the vehicle-treated control animals, whereas a reversal of the inhibition of chondrocyte proteoglycan synthesis was found in the anti-IL-18-exposed animals. Blockade of endogenous IL-18 in IFN-gamma-deficient mice showed results similar to those found in wild-type animals, identifying a role for IL-18 that is IFN-gamma independent. The present study indicates that IL-18 is a proinflammatory cytokine during the onset of murine SCW arthritis, and this inflammatory role of IL-18 is IFN-gamma independent.

IL-4 gene therapy for collagen arthritis suppresses synovial IL-17 and osteoprotegerin ligand and prevents bone erosion

Bone destruction is the most difficult target in the treatment of rheumatoid arthritis (RA). Here, we report that local overexpression of IL-4, introduced by a recombinant human type 5 adenovirus vector (Ad5E1mIL-4) prevents joint damage and bone erosion in the knees of mice with collagen arthritis (CIA). No difference was noted in the course of CIA in the injected knee joints between Ad5E1mIL-4 and the control vector, but radiographic analysis revealed impressive reduction of joint erosion and more compact bone structure in the Ad5E1mIL-4 group. Although severe inflammation persisted in treated mice, Ad5E1mIL-4 prevented bone erosion and diminished tartrate-resistant acid phosphatase (TRAP) activity, indicating that local IL-4 inhibits the formation of osteoclast-like cells. Messenger RNA levels of IL-17, IL-12, and cathepsin K in the synovial tissue were suppressed, as were IL-6 and IL-12 protein production. Osteoprotegerin ligand (OPGL) expression was markedly suppressed by local IL-4, but no loss of OPG expression was noted with Ad5E1mIL-4 treatment. Finally, in in vitro studies, bone samples of patients with arthritis revealed consistent suppression by IL-4 of type I collagen breakdown. IL-4 also enhanced synthesis of type I procollagen, suggesting that it promoted tissue repair. These findings may have significant implications for the prevention of bone erosion in arthritis.

Reduction of interleukin-17-induced inhibition of chondrocyte proteoglycan synthesis in intact murine articular cartilage by interleukin-4

OBJECTIVE

To investigate the role of interleukin-4 (IL-4) and IL-10 in basal and IL-1- and IL-17-mediated inhibition of chondrocyte metabolism.

METHODS

Cartilage explants of patellae from naive mice were incubated with IL-17 and/or IL-1 alone or were pretreated with IL-4 and IL-10. In addition, knee joints of naive mice were injected intraarticularly with IL-4 and IL-10 alone or were coinjected with IL-1. Chondrocyte proteoglycan (PG) synthesis was measured in intact murine articular cartilage. Levels of nitric oxide (NO) were measured using the Griess reagent.

RESULTS

IL-17, a novel cytokine secreted by CD4+ activated memory T cells, inhibited chondrocyte PG synthesis in intact murine articular cartilage, although the suppressive effect was less potent than that of IL-1. The suppressive effect of IL-17 was completely abolished in the presence of L-NIO (L-NS-[1-iminoethyl]ornithine), an inhibitor of NO metabolism, and IL-17 only slightly induced inhibition of PG synthesis in cartilage explants of patellae from iNOS (inducible NO synthase) knockout mice. This indicates that the suppressive effect of IL-17 was mediated by NO. Pretreatment with IL-4, but not IL-10, significantly reduced the inhibition of chondrocyte PG synthesis induced by IL-1 or IL-17. The IL-4-induced reduction in the inhibitory effects of IL-1 and IL-17 on chondrocyte PG synthesis was accompanied by decreased NO formation in the culture supernatants.

CONCLUSION

IL-17 plays a role in the inhibition of chondrocyte PG synthesis. IL-4 and IL-10 have no effect on basal chondrocyte metabolism. However, IL-4-pretreated cartilage is less sensitive to the suppressive effect of IL-1 as well as IL-17. This suggests that IL-4 is protective in T cell-driven cartilage disturbances, probably through reduction of iNOS.

Intra-articular IL-10 gene transfer regulates the expression of collagen-induced arthritis (CIA) in the knee and ipsilateral paw

We studied the effects of local IL-10 application, introduced by a recombinant human type 5 adenovirus vector, in the mouse knee joint during the early phase of CIA. One intra-articular injection with the IL-10-expressing virus (Ad5E1mIL-10) caused substantial over-expression of IL-10 in the mouse knee joint, using virus dosages which did not induce distracting inflammation. High expression of IL-10 was noted for a few days, being maximal at day 1. One intra-articular injection of Ad5E1mIL-10 in the knee joints of collagen type II (CII)-immunized mice, before onset of CIA was noted, reduced the incidence of collagen arthritis in that knee. Of high interest, the protective effect of local IL-10 expression by Ad5E1mIL-10 was not restricted to the knee joint alone. The arthritis incidence in the ipsilateral paw was highly suppressed. In contrast, local IL-10 over-expression was not effective when treatment was started after onset of CIA. Further analysis in the acute streptococcal cell wall-induced arthritis model revealed that local IL-10 over-expression markedly suppressed the production of tumour necrosis factor-alpha (TNF-alpha) and IL-1alpha, but had no significant effect on IL-1beta and IL-12 production in the inflamed synovium. These data indicate that local over-expression of IL-10 in the knee joint of mice regulates the expression of collagen arthritis, probably through down-regulation of TNF-alpha.

Blockade of endogenous interleukin 12 results in suppression of murine streptococcal cell wall arthritis by enhancement of interleukin 10 and interleukin 1Ra

OBJECTIVE

The goal of this study was to investigate the role of endogenous interleukin 12 (IL12) in acute murine streptococcal cell wall (SCW) arthritis.

METHODS

C57black/6 mice were injected intraperitoneally with rat anti-murine IL12 (C17.8), shortly before induction of arthritis by intra-articular injection of 25 microg SCW fragments into the right knee joint. Joint swelling and chondrocyte synthetic function was analysed several days after induction of SCW arthritis. Local cytokine profile was determined, protein by using ELISA and mRNA by RT-PCR technology. To confirm the findings at later time points, tissue chamber model of inflammation was used. Histology was performed to examine cell influx and cartilage damage.

RESULTS

Suppression of joint swelling was noted at days 2 and 4, whereas no suppressive effect of anti-IL12 was found at day 1. Severe inhibition of chondrocyte proteoglycan synthesis was seen at day 1 in both arthritic control and anti-IL12 treated mice. However, chondrocyte function was restored at day 4 of arthritis in the anti-IL12 injected animals, but not in the arthritic controls. Moreover, cell influx in synovial tissue and joint cavity was reduced by anti-IL12 treatment. Neutralisation of IL12 reduced the local levels of IL1beta, IL12 and interferon gamma, when examined shortly after induction of SCW arthritis, whereas tumour necrosis factor alpha levels were not affected. In contrast, IL10 and IL1Ra protein and mRNA levels were strongly up regulated in synovial tissues after IL12 blockade. Enhancement of IL10 and IL1Ra by anti-IL12 was confirmed in a tissue chamber model with SCW induced inflammation.

CONCLUSIONS

This study indicates that IL12 is a pro-inflammatory cytokine during onset of acute SCW arthritis. Balances of proinflammatory and anti-inflammatory cytokines were strongly improved by anti-IL12 treatment.

Neutralization of IL-18 reduces neutrophil tissue accumulation and protects mice against lethal Escherichia coli and Salmonella typhimurium endotoxemia

In addition to stimulating IFN-gamma synthesis, IL-18 also possesses inflammatory effects by inducing synthesis of the proinflammatory cytokines TNF and IL-1beta and the chemokines IL-8 and macrophage inflammatory protein-1alpha. We hypothesized that neutralization of IL-18 would have a beneficial effect in lethal endotoxemia in mice. IL-1beta converting enzyme (ICE)-deficient mice, lacking the ability to process mature IL-18 and IL-1beta, were completely resistant to lethal endotoxemia induced by LPS derived from either Escherichia coli or Salmonella typhimurium. In contrast, both wild-type and IL-1beta-/- mice were equally susceptible to the lethal effects of LPS, implicating that absence of mature IL-18 or IFN-gamma but not IL-1beta in ICE-/- mice is responsible for this resistance. However, IFN-gamma-deficient mice were not resistant to S. typhimurium LPS, suggesting an IFN-gamma-independent role for IL-18. Anti-IL-18 Abs protected mice against a lethal injection of either LPS. Anti-IL-18 treatment also reduced neutrophil accumulation in liver and lungs. The increased survival was accompanied by decreased levels of IFN-gamma and macrophage inflammatory protein-2 in anti-IL-18-treated animals challenged with E. coli LPS, whereas IFN-gamma and TNF concentrations were decreased in treated mice challenged with S. typhimurium. In conclusion, neutralization of IL-18 during lethal endotoxemia protects mice against lethal effects of LPS. This protection is partly mediated through inhibition of IFN-gamma production, but mechanisms involving decreased neutrophil-mediated tissue damage due to the reduction of either chemokines (E. coli LPS) or TNF (S. typhimurium LPS) synthesis by anti-IL-18 treatment may also be involved.

Induction of tolerance with intranasal administration of human cartilage gp-39 in DBA/1 mice: amelioration of clinical, histologic, and radiologic signs of type II collagen-induced arthritis

OBJECTIVE

Human cartilage glycoprotein 39 (HC gp-39) was recently identified as a candidate autoantigen in the pathogenesis of rheumatoid arthritis. In the present studies, we investigated the capacity of HC gp-39 to interfere in clinical disease induced by an unrelated autoantigen, type II collagen (CII), by the induction of cross-tolerance.

METHODS

DBA-1j/Bom mice were immunized with bovine CII/complete Freund's adjuvant and were given intraperitoneal booster injections of CII on day 21. Tolerance was induced via the intranasal pathway with either the disease-inducing antigen (CII), a control antigen (ovalbumin), or HC gp-39 either before priming with CII or near the day of the booster injection. Arthritis was monitored visually, and joint pathology was examined histologically and radiologically. In addition, CII antibody levels in serum were analyzed by enzyme-linked immunosorbent assay.

RESULTS

In contrast to treatment before priming, intranasal application of HC gp-39 after immunization markedly suppressed disease activity and prevented joint destruction, whereas application of ovalbumin or CII was ineffective. Interference of HC gp-39 with the immune response to CII was demonstrated by decreased anti-CII antibody levels. The combined data indicate that intranasal treatment with HC gp-39 may trigger modulatory or regulatory mechanisms that interfere with the expression of disease in murine collagen-induced arthritis.

CONCLUSION

HC gp-39 is the first cross-tolerance-inducing protein in arthritis that down-modulates a spectrum of disease features when given in a semitherapeutic protocol.

Role of tumour necrosis factor alpha in experimental arthritis: separate activity of interleukin 1beta in chronicity and cartilage destruction

Chronic arthritis is characterised by persistent joint inflammation and concomitant joint destruction. Using murine arthritis models and neutralising antibodies as well as cytokine specific knockout conditions, it was found that tumour necrosis factor alpha (TNFalpha) is important in early joint swelling. Membrane bound TNFalpha is sufficient to drive this aspect of inflammation as well as the acute cellular infiltrate in the synovial tissue. Interleukin 1 (IL1) is not necessarily a dominant cytokine in early joint swelling, but has a pivotal role in sustained cellular infiltration and erosive cartilage damage. TNFalpha independent IL1 production is a prominent feature in murine arthritis models. These observations provide evidence for potential uncoupling of joint inflammation and erosive changes, implying that both cytokines need to be targeted to achieve optimal treatment.

IL-1 alpha beta blockade prevents cartilage and bone destruction in murine type II collagen-induced arthritis, whereas TNF-alpha blockade only ameliorates joint inflammation

Anti-TNF-alpha treatment of rheumatoid arthritis patients markedly suppresses inflammatory disease activity, but so far no tissue-protective effects have been reported. In contrast, blockade of IL-1 in rheumatoid arthritis patients, by an IL-1 receptor antagonist, was only moderately effective in suppressing inflammatory symptoms but appeared to reduce the rate of progression of joint destruction. We therefore used an established collagen II murine arthritis model (collagen-induced arthritis(CIA)) to study effects on joint structures of neutralization of either TNF-alpha or IL-1. Both soluble TNF binding protein and anti-IL-1 treatment ameliorated disease activity when applied shortly after onset of CIA. Serum analysis revealed that early anti-TNF-alpha treatment of CIA did not decrease the process in the cartilage, as indicated by the elevated COMP levels. In contrast, anti-IL-1 treatment of established CIA normalized COMP levels, apparently alleviating the process in the tissue. Histology of knee and ankle joints corroborated the finding and showed that cartilage and joint destruction was significantly decreased after anti-IL-1 treatment but was hardly affected by anti-TNF-alpha treatment. Radiographic analysis of knee and ankle joints revealed that bone erosions were prevented by anti-IL-1 treatment, whereas the anti-TNF-alpha-treated animals exhibited changes comparable to the controls. In line with these findings, metalloproteinase activity, visualized by VDIPEN production, was almost absent throughout the cartilage layers in anti-IL-1-treated animals, whereas massive VDIPEN appearance was found in control and sTNFbp-treated mice. These results indicate that blocking of IL-1 is a cartilage- and bone-protective therapy in destructive arthritis, whereas the TNF-alpha antagonist has little effect on tissue destruction.

TNF alpha and IL-1 beta are separate targets in chronic arthritis

Chronic arthritis is characterized by persistent joint inflammation and concomitant joint destruction. Using murine arthritis models and neutralizing antibodies as well as cytokine-specific knockout conditions, it was found that tumor necrosis factor alpha (TNF alpha) is important in joint swelling, whereas a direct role in tissue destruction is unlikely. Interleukin-1 (IL-1) is not a dominant cytokine in early joint swelling, but has a pivotal role in sustained cell infiltration and erosive cartilage damage. TNF alpha-independent IL-1 production is a prominent feature in murine arthritis models, implying that IL-1 as well as TNF alpha are appropriate targets for therapy. These observations provide evidence for the potential uncoupling of joint inflammation and erosive changes and underline the need for TNF alpha/IL-1 directed combination-therapy approaches.

Adenoviral vector-mediated overexpression of IL-4 in the knee joint of mice with collagen-induced arthritis prevents cartilage destruction

Rheumatoid arthritis is a chronic inflammatory joint disease, leading to cartilage and bone destruction. In this study, we investigated the effects of local IL-4 application, introduced by a recombinant human type 5 adenovirus vector, in the knee joint of mice with collagen-induced arthritis. One intraarticular injection with an IL-4-expressing virus caused overexpression of IL-4 in the mouse knee joint. Enhanced onset and aggravation of the synovial inflammation were found in the IL-4 group. However, despite ongoing inflammation, histologic analysis showed impressive prevention of chondrocyte death and cartilage erosion. In line with this, chondrocyte proteoglycan synthesis was enhanced in the articular cartilage. This was quantified with ex vivo 35S-sulfate incorporation in patellar cartilage and confirmed by autoradiography on whole knee joint sections. Reduction of cartilage erosion was further substantiated by lack of expression of the stromelysin-dependent cartilage proteoglycan breakdown neoepitope VDIPEN in the Ad5E1 mIL-4-treated knee joint. Reduced metalloproteinase activity was also supported by markedly diminished mRNA expression of stromelysin-3 in the synovial tissue. Histologic analysis revealed marked reduction of polymorphonuclear cells in the synovial joint space in the IL-4-treated joints. This was confirmed by immunolocalization studies on knee joint sections using NIMP-R14 staining and diminished mRNA expression of macrophage-inflammatory protein-2 in the synovium tissue. mRNA levels of TNF-alpha and IL-1beta were suppressed as well, and IL-1beta and nitric oxide production by arthritic synovial tissue were strongly reduced. Our data show an impressive cartilage-protective effect of local IL-4 and underline the feasibility of local gene therapy with this cytokine in arthritis.

Animal models of arthritis in NOS2-deficient mice

OBJECTIVE

To study the role of nitric oxide (NO) in cartilage destruction in murine models of arthritis and osteoarthritis.

METHODS

Joint inflammation was induced in the knee joint by intraarticular injection of Zymosan. Osteoarthritis was induced by local injection of bacterial collagenase, causing joint instability. The effect of NO deficiency was studied by comparing the effects in normal mice and mice with genetically disrupted NOS2 (inducible NO synthase). Impact on articular cartilage was evaluated by histology and measurement of chondrocyte 35S-proteoglycan synthesis.

RESULTS

NOS2 deficiency prevented chondrocyte proteoglycan synthesis inhibition in the arthritic cartilage and restored normal responsiveness to IGF-1. Net cartilage proteoglycan depletion was markedly reduced in the absence of NOS2, although inflammation was hardly affected. Osteoarthritic joint pathology was also significantly reduced, including diminished cartilage lesions and osteophyte formation.

CONCLUSION

NO plays a major role in cartilage damage in both arthritic and osteoarthritic conditions.

Synergistic protection against cartilage destruction by low dose prednisolone and interleukin-10 in established murine collagen arthritis

OBJECTIVE

To investigate potential synergy of low dosages glucocorticosteroids (GC's) and interleukin-10 (IL-10), using established murine collagen-induced arthritis (CIA) as a model.

METHODS

DBA-1J/BOM mice were immunized with bovine type II collagen and boosted at day 21. Mice with established CIA were selected and treated for at least 7 days with either prednisolone (0.05-5 mg/kg), IL-10 (0.1-5 micrograms/day) or the combination of prednisolone/IL-10 (0.05/1 and 0.05/5). Arthritis score was monitored visually, and joint pathology was examined by histology, and serum cartilage oligomeric matrix protein (COMP) measured.

RESULTS

Amelioration of CIA was found with dosages of 1 and 5 mg/kg prednisolone, while a dose of 0.05 mg/kg prednisolone was ineffective. Treatment of CIA with 5 micrograms/day IL-10 resulted in a mild, but significant suppression. Synergistic effects were seen with the combination of low dose prednisolone and IL-10 (0.05 mg/kg, 1 microgram/day). Both arthritis score and joint pathology were significantly reduced. Moreover, COMP levels were significantly decreased after IL-10/prednisolone treatment, confirming decreased cartilage involvement. Of great interest, treatment of CIA with prednisolone/IL-10 markedly reduced IL-1 beta and enhanced IL-10 production by synovial tissue. In addition, synovial mRNA levels for IL-1 beta were decreased, while mRNA levels for IL-10 and IL-1Ra were upregulated by combined treatment.

CONCLUSION

This study demonstrates synergistic effects of combined treatment with prednisolone and IL-10 on suppressing disease activity of CIA as well as reducing cartilage.

Protection against cartilage and bone destruction by systemic interleukin-4 treatment in established murine type II collagen-induced arthritis

INTRODUCTION

Rheumatoid arthritis (RA) is associated with an increased production of a range of cytokines including tumour necrosis factor (TNF)-alpha and interleukin (IL)-1, which display potent proinflammatory actions that are thought to contribute to the pathogenesis of the disease. Although TNF-alpha seems to be the major cytokine in the inflammatory process, IL-1 is the key mediator with regard to cartilage and bone destruction. Apart from direct blockage of IL-1/TNF, regulation can be exerted at the level of modulatory cytokines such as IL-1 and IL-10. IL-4 is a pleiotropic T-cell derived cytokine that can exert either suppressive or stimulatory effects on different cell types, and was originally identified as a B-cell growth factor and regulator of humoral immune pathways. IL-4 is produced by activated CD4+T cells and it promotes the maturation of TH2 cells. IL-4 stimulates proliferation, differentiation and activation of several cell types, including fibroblasts, endothelial cells and epithelial cells. IL-4 is also known to be a potent anti-inflammatory cytokine that acts by inhibiting the synthesis of proinflammatory cytokines such as IL-1, TNF-alpha, IL-6, IL-8 and IL-12 by macrophages and monocytes. Moreover, IL-4 stimulates the synthesis of several cytokine inhibitors such as interleukin-1 receptor antagonist (IL-1Ra), soluble IL-1-receptor type II and TNF receptors IL-4 suppresses metalloproteinase production and stimulates tissue inhibitor of metalloproteinase-1 production in human mononuclear phagocytes and cartilage explants, indicating a protective effect of IL-4 towards extracellular matrix degradation. Furthermore, IL-4 inhibits both osteoclast activity and survival, and thereby blocks bone resorption in vitro. Of great importance is that IL-4 could not be detected in synovial fluid or in tissues. This absence of IL-4 in the joint probably contributes to the disturbance in the Th1/Th2 balance in chronic RA. Collagen-induced arthritis (CIA) is a widely used model of arthritis that displays several features of human RA. Recently it was demonstrated that the onset of CIA is under stringent control of IL-4 and IL-10. Furthermore, it was demonstrated that exposure to IL-4 during the immunization stage reduced onset and severity of CIA. However, after cessation of IL-4 treatment disease expression increased to control values.

AIMS

Because it was reported that IL-4 suppresses several proinflammatory cytokines and matrix degrading enzymes and upregulates inhibitors of both cytokines and catabolic enzymes, we investigated the tissue protective effect of systemic IL-4 treatment using established murine CIA as a model. Potential synergy of low dosages of anti-inflammatory glucocorticosteroids and IL-4 was also evaluated.

METHODS

DBA-1J/Bom mice were immunized with bovine type II collagen and boosted at day 21. Mice with established CIA were selected at day 28 after immunization and treated for days with IL-4, prednisolone, or combinations of prednisolone and IL-4. Arthritis score was monitored visually. Joint pathology was evaluated by histology, radiology and serum cartilage oligomeric matrix protein (COMP). In addition, serum levels of IL-1Ra and anticollagen antibodies were determined.

RESULTS

Treatment of established CIA with IL-4 (1microgram/day) resulted in suppression of disease activity as depicted in Figure 1. Of great interest is that, although 1 microgram/day IL-4 had only a moderate effect on the inflammatory component of the disease activity, it strongly reduced cartilage pathology, as determined by histological examination (Fig. 1). Moreover, serum COMP levels were significantly reduced, confirming decreased cartilage involvement. In addition, both histological and radiological analysis showed that bone destruction was prevented (Fig. 1). Systemic IL-4 administration increased serum IL-1Ra levels and reduced anticollagen type II antibody levels. Treatment with low-dose IL-4 (0.1 microgram/day) was ineffective in suppressing disease score, serum COMP or joint destruction. Synergistic suppression of both arthritis severity and COMP levels was noted when low-dose IL-4 was combined with prednisolone (0.05 mg/kg/day), however, which in itself was not effective.

DISCUSSION

In the present study, we demonstrate that systemic IL-4 treatment ameliorates disease progression of established CIA. Although clinical disease progression of established CIA. Although clinical disease progression was only arrested and not reversed, clear protection against cartilage and bone destruction was noted. This is in accord with findings in both human RA and animal models of RA that show that inflammation and tissue destruction sometimes are uncoupled processes. Of great importance is that, although inflammation was still present, strong reduction in serum COMP was found after exposure to IL-4. This indicated that serum COMP levels reflected cartilage damage, although a limited contribution of the inflamed synovium cannot be excluded. Increased serum IL-1Ra level (twofold) was found after systemic treatment with IL-4, but it is not likely that this could explain the suppression of CIA. We and others have reported that high dosages of IL-1Ra are needed for marked suppression of CIA. As reported previously, lower dosages of IL-4 did not reduce clinical disease severity of established CIA. Of importance is that combined treatment of low dosages of IL-4 and IL-10 appeared to have more potent anti-inflammatory effects, and markedly protected against cartilage destruction. Improved anti-inflammatory effect was achieved with IL-4/prednisolone treatment. In addition, synergistic effects were found for the reduction of cartilage and bone destruction. This indicates that systemic IL-4/prednisolone treatment may provide a cartilage and bone protective therapy for human RA.

Different roles of tumour necrosis factor alpha and interleukin 1 in murine streptococcal cell wall arthritis

In this study two different aspects of tumour necrosis factor alpha (TNF-alpha) and interleukin 1 (IL-1) in locally induced murine streptococcal cell wall arthritis (SCW) were investigated. First, the kinetics and interdependence of TNF-alpha and IL-1 release; and second; their involvement in inflammation and cartilage destruction. Kinetic studies showed that the TNF-alpha peak level preceded the IL-1 peak level. However, in vivo neutralization of TNF-alpha did not result in decreased IL-1 bioactivity or immunoreactivity, suggesting that there is no dominant TNF-alpha-dependent IL-1 release in this model. Inflammation was studied by measuring knee joint swelling and inflammatory cell influx. Impact on cartilage was studied by measuring chondrocyte proteoglycan synthesis and cartilage proteoglycan depletion. The role of TNF-alpha in these phenomena was investigated using anti-TNF-alpha antibodies and tumour necrosis factor binding protein (TNFbp). Similarly, the role of IL-1 was studied using anti-IL-1 antibodies or IL-1 receptor antagonist (IL-1Ra). Anti-TNF-alpha treatment significantly reduced joint swelling, whereas this effect was not found by using anti-IL-1 or IL-1Ra. In contrast, neutralization of IL-1, but not TNF-alpha, resulted in a significant decrease of chondrocyte proteoglycan synthesis inhibition. Moreover, histology revealed that anti-IL-1 treatment reduced cartilage proteoglycan depletion and inflammatory cell influx. Combined anti-TNF-alpha/anti-IL-1 treatment significantly suppressed both inflammation and cartilage damage. However, the impact on these separate parameters did not exceed the effects of either anti-TNF-alpha or anti-TNF-1. It can be concluded that both TNF-alpha and IL-1 exert specific activities in SCW arthritis. The involvement of TNF-alpha in this model is limited to joint swelling, whereas IL-1 plays a dominant role in cartilage destruction and inflammatory cell influx.

Regulatory role of interleukin 10 in joint inflammation and cartilage destruction in murine streptococcal cell wall (SCW) arthritis. More therapeutic benefit with IL-4/IL-10 combination therapy than with IL-10 treatment alone

Interleukin 10 (IL-10) and IL-4 are important downregulators of a number of macrophage functions. The authors investigated the role of endogenous IL-4 and IL-10 and the therapeutic effect of addition of these cytokines on joint inflammation and cartilage destruction in the early stages of the macrophage dependent murine streptococcal cell wall (SCW) arthritis model. It was demonstrated that endogenous IL-10, but not IL-4, plays a pivotal role in the regulation of SCW arthritis. Blocking endogenous IL-10 with anti-IL-10 antibodies resulted in a sustained arthritis with more dense synovial infiltrate as well as enhanced cartilage damage. Adding exogenous IL-10 further enlarged the suppressive effect of endogenous IL-10. Even more pronounced amelioration was found with the combination IL-4/IL-10. This resulted in a reduced swelling and a restorative overshoot in chondrocyte proteoglycan synthesis at day 4 (140%). Treatment with the combination IL-4/IL-10 not only a marked reduction of tumour necrosis factor alpha (TNF-alpha) levels, like IL-10 treatment alone, but also the IL-1 beta levels were strongly reduced in the synovium. In conclusion, the data is consistent with a dominant role of IL-10 in natural suppression of arthritis expression, whereas combined treatment with IL-4 and IL-10 appears to be of potential therapeutic value.

Dual role of IL-12 in early and late stages of murine collagen type II arthritis

IL-12 can promote Th1 responses, and early administration of IL-12 during immunization was shown to enhance expression of autoimmune collagen-induced arthritis (CIA). We now studied the impact of IL-12 at the stage of disease expression and during established CIA in DBA-1 mice. Accelerated onset and enhanced severity were provoked when i.p. injections of 100 ng of murine IL-12 (mIL-12) were given around the time of arthritis onset. Moreover, the onset of CIA could be ameliorated with anti-mIL-12 Abs, indicating that IL-12 is a pivotal mediator in the expression of CIA. In addition, the effect of anti-mIL-12 treatment was analyzed in established CIA. Continued treatment did not suppress established arthritis. Instead, these mice showed an impressive exacerbation of arthritis shortly after cessation of anti-mIL-12 treatment, indicative of impairment of endogenous control. Exaggerated disease was characterized by massive granulocyte influx and enhanced expression of IL-1 beta and TNF-alpha mRNA in the synovial tissue. Subsequently, we treated established collagen arthritis with recombinant mIL-12 for 7 days. Profound suppression of the arthritis score was noted, including reduced influx of cells and diminished cartilage damage. Tenfold enhanced levels of IL-10 were detected in sera of mIL-12-treated mice, and up-regulated mRNA levels of IL-10, IFN-gamma, and IL-12 were measured in synovial tissue. Finally, the anti-inflammatory effect of IL-12 on CIA could be reversed by coadministration of anti-IL-10 Abs. This study indicates that IL-12 has a stimulatory role in early arthritis expression, whereas it has a suppressive role in the established phase of collagen arthritis.

Dual role of IL-12 in early and late stages of murine collagen type II arthritis

IL-12 can promote Th1 responses, and early administration of IL-12 during immunization was shown to enhance expression of autoimmune collagen-induced arthritis (CIA). We now studied the impact of IL-12 at the stage of disease expression and during established CIA in DBA-1 mice. Accelerated onset and enhanced severity were provoked when i.p. injections of 100 ng of murine IL-12 (mIL-12) were given around the time of arthritis onset. Moreover, the onset of CIA could be ameliorated with anti-mIL-12 Abs, indicating that IL-12 is a pivotal mediator in the expression of CIA. In addition, the effect of anti-mIL-12 treatment was analyzed in established CIA. Continued treatment did not suppress established arthritis. Instead, these mice showed an impressive exacerbation of arthritis shortly after cessation of anti-mIL-12 treatment, indicative of impairment of endogenous control. Exaggerated disease was characterized by massive granulocyte influx and enhanced expression of IL-1 beta and TNF-alpha mRNA in the synovial tissue. Subsequently, we treated established collagen arthritis with recombinant mIL-12 for 7 days. Profound suppression of the arthritis score was noted, including reduced influx of cells and diminished cartilage damage. Tenfold enhanced levels of IL-10 were detected in sera of mIL-12-treated mice, and up-regulated mRNA levels of IL-10, IFN-gamma, and IL-12 were measured in synovial tissue. Finally, the anti-inflammatory effect of IL-12 on CIA could be reversed by coadministration of anti-IL-10 Abs. This study indicates that IL-12 has a stimulatory role in early arthritis expression, whereas it has a suppressive role in the established phase of collagen arthritis.

Prevention of murine collagen-induced arthritis in the knee and ipsilateral paw by local expression of human interleukin-1 receptor antagonist protein in the knee

OBJECTIVE

To determine the efficacy of local human interleukin-1 receptor antagonist (HuIL-1Ra) gene therapy in murine collagen-induced arthritis (CIA).

METHODS

DBA/1 mice were immunized against bovine type II collagen. Before the onset of arthritis, NIH/3T3 fibroblasts transfected with pMFG-IRAP were transplanted into the knee cavity. Normal NIH/3T3 cells served as controls. Paws were evaluated macroscopically for redness, swelling, and deformities during the course of arthritis. Swelling of the knee joints was measured by external gamma counting of 99mtechnetium accumulation in the joint. Paws and knee joints were dissected and processed for histologic studies to evaluate inflammation and cartilage destruction.

RESULTS

The NIH/3T3 fibroblasts survived in the joint cavity of DBA mice for at least 7 days. The transduced cells expressed immunoreactive and bioactive HuIL-1Ra in the knee joint, and produced sufficient amounts to block the effect of 1 ng of recombinant murine IL-1alpha on chondrocyte proteoglycan synthesis. The onset of CIA was almost completely prevented in knee joints containing HuIL-1Ra-producing cells, whereas joints containing normal cells showed severe inflammation and destruction of cartilage. Moreover, onset of CIA in the draining joints (ipsilateral paws) of the HuIL-1Ra gene-bearing knees was also prevented.

CONCLUSION

Local production of HuIL-1Ra in the knee was able to ameliorate the effects of IL-1 on cartilage and could prevent the onset of CIA not only in that knee, but also in the "draining" paw. This indicates the feasibility of gene transfer as a therapeutic approach to modulating arthritis.

Role of interleukin-4 and interleukin-10 in murine collagen-induced arthritis. Protective effect of interleukin-4 and interleukin-10 treatment on cartilage destruction

OBJECTIVE

To examine the role of endogenous interleukin-4 (IL-4) and interleukin-10 (IL-10) and the therapeutic effect of the addition of IL-4 and IL-10 in early and established murine collagen-induced arthritis (CIA).

METHODS

Murine recombinant IL-4, IL-10, or the combination was given intraperitoneally twice daily from the day of arthritis onset up to 7-10 days of CIA in DBA/1 mice. Anti-IL-4, anti-IL-10, or both antibodies were given intraperitoneally before or after the onset of CIA. The effect of cytokine or anticytokine treatment was monitored visually by macroscopic scoring. Histology and reverse transcription-polymerase chain reaction (RT-PCR) analyses were performed at the end of the treatment period.

RESULTS

IL-4 alone did not provoke any effect, IL-10 slightly suppressed the arthritis, but a more pronounced amelioration was found with the combination. This cooperative effect was noted after early treatment but also occurred when the start of treatment was delayed until 1 week after onset. Apart from suppression of macroscopic signs of inflammation, combined treatment with IL-4/IL-10 also reduced cellular infiltrates in the synovial tissue and caused pronounced protection against cartilage destruction. Moreover, levels of mRNA for tumor necrosis factor alpha (TNF alpha) and IL-1 were highly suppressed both in the synovial tissue and in the articular cartilage. In contrast, levels of IL-1 receptor antagonist (IL-1Ra) mRNA remained elevated, which suggests that the mechanism of protection may be related to suppressed production of TNF alpha and IL-1, with concomitant up-regulation of the IL-1Ra/IL-1 balance. However, accelerated onset of CIA and increased severity could be achieved with neutralizing anti-IL-10 antibodies. This expression could be further optimized with a combination of anti-IL-4 and anti-IL-10 antibodies, although anti-IL-4 alone was without effect.

CONCLUSION

Our data are consistent with a dominant role of IL-10 in the natural suppression of arthritis expression, whereas combined treatment with IL-4 and IL-10 appears of potential therapeutic value, not only at the onset, but also in established arthritis.

Quantification of mRNA levels in joint capsule and articular cartilage of the murine knee joint by RT-PCR: kinetics of stromelysin and IL-1 mRNA levels during arthritis

We developed a method to isolate well defined joint specimens from different compartments of normal and arthritic murine knee joints in which mRNA levels of stromelysin and IL-1 were semiquantified using RT-PCR. Joint capsule specimens were isolated on medial and lateral sides of the patella with a biopsy punch. Cartilage layers were isolated from patellae after a mild decalcification with EDTA. EDTA treatment had no effect on the amount and efficiency of amplification of mRNA when tested on isolated chondrocytes. After induction of experimental arthritis, stromelysin mRNA was elevated approximately 50 times in both joint capsule and cartilage. IL-1 was elevated 100 times in joint capsule but only 10 times in cartilage. Kinetic analysis of mRNA levels in cartilage during arthritis showed a prolonged elevation of stromelysin mRNA compared to IL-1. The variation in mRNA levels between joints of individual mice proved to be low, showing that sampling of the specimens and subsequent RT-PCR can be performed reliably. The current method offers a valuable approach to study gene expression in knee joints during murine experimental arthritis.

Localization of insulin-like growth factor-1 receptor in human normal and osteoarthritic cartilage in relation to proteoglycan synthesis and content

Insulin-like growth factor-1 (IGF-1) plays a key role in the regulation of chondrocyte proteoglycan (PG) metabolism. We investigated whether chondrocyte PG synthetic activity correlates with the presence of chondrocyte IGF-1 receptor in the surface, middle and deeper zones of normal human articular cartilage and in cartilage known to display a shift in chondrocyte metabolism, i.e. cultured cartilage or osteoarthritic (OA) cartilage. Cartilage specimens were obtained post mortem from human knees within 18 h after death from donors without known clinical OA history. The samples were taken from macroscopically normal looking regions as well as from damaged regions with osteoarthritic appearance, yielding a range of OA grades from mild to moderate and severe OA. We examined chondrocyte PG synthesis by in situ autoradiography of incorporated [35S]sulphate and chondrocyte IGF-1 receptor localization by immunohistochemistry, followed by confocal laser scanning microscopical (CLSM) analysis in the same cartilage samples. In normal cartilage, both the amount of chondrocyte PG synthesis and the level of chondrocyte IGF-1 receptor localization are at low levels in the surface zone chondrocytes, but both are high in middle and deeper zone chondrocytes. Furthermore, after culture, the increase in chondrocyte PG synthesis in the surface layer coincides with increase in IGF-1 receptor expression. However, in mild OA particularly high levels of chondrocyte synthetic activity were found in the upper cartilage layer, whereas IGF-1 receptor expression was low in this layer, suggesting that factors other than IGF-1 are involved. High chondrocyte PG synthetic activity and chondrocyte IGF-1 receptor staining were found in the upper and deeper layers of moderate OA cartilage, whereas both low levels of chondrocyte activity as well as IGF-1 receptors were observed in cases of severe OA. Our data indicate that IGF-1 displays cellular heterogeneity in chondrocyte stimulation in the various cartilage zones in normal cartilage. Clear zonal correlation is lost in OA cartilage, and patterns of chondrocyte IGF-1 receptor expression and PG synthesis vary with the stage of OA.

Phagocytic lining cells determine local expression of inflammation in type II collagen-induced arthritis

OBJECTIVE

To investigate the in vivo role of phagocytic synovial lining cells in the local expression of inflammation in type II collagen-induced arthritis (CIA) in DBA/1J mice.

METHODS

On various days before arthritis induction (day 7, 5, or 2), phagocytic lining cells were selectively depleted from the synovial layer by injecting multilamellar liposomes containing clodronate (dichloromethylene diphosphonate) directly into the knee joints. As controls, either PBS or PBS-laden liposomes were injected. CIA was induced by immunizing mice with heterologous bovine type II collagen in Freund's complete adjuvant. Arthritis onset was synchronized by a single intraperitoneal injection of lipopolysaccharide; arthritis was evaluated in hematoxylin and eosinstained knee joint sections. Chemotactic activity in synovial washout samples was detected in a Transwell chemotactic assay. Interleukin-1 (IL-1) and tumor necrosis factor alpha (TNF alpha) protein levels were measured in NOB-1 and L929 bioassays, respectively. IL-1 messenger RNA (mRNA) in synovial specimens was measured by reverse transcriptase-polymerase chain reaction. IL-1 was also detected immunohistologically in knee joint sections.

RESULTS

In clodronate-laden liposome-treated, lining-depleted knee joints, there was significantly decreased inflammation compared with controls. Cell influx into the synovium was markedly decreased. Expression of IL-1 mRNA in the synovium was significantly reduced. IL-1 was detected only in some cells in the deeper synovial layer, in contrast to controls, in which large numbers of cells in the deeper synovial layer were stained. In synovial washouts from lining-depleted knee joints, biologically active IL-1 levels were reduced by 40% at 6 hours after arthritis induction. Most strikingly, chemotactic activity was highly decreased in these synovial washout samples. When IL-1 or TNF alpha was injected into the knee joints of immunized mice in which arthritis was not yet expressed, arthritis was not induced in the lining-depleted joints, whereas marked cell influx was found in control joints.

CONCLUSION

Our data indicate that phagocytic lining cells play a crucial role in the local expression of inflammation in systemically induced CIA. Phagocytic lining cells probably form an important source of chemotactic factors which are set free upon activation by IL-1 or TNF alpha.

Anticytokine treatment of established type II collagen-induced arthritis in DBA/1 mice. A comparative study using anti-TNF alpha, anti-IL-1 alpha/beta, and IL-1Ra

OBJECTIVE

To examine the role of tumor necrosis factor alpha (TNF alpha), interleukin-1 alpha (IL-1 alpha), and IL-1 beta in collagen-induced arthritis (CIA), immediately after onset and during the phase of established arthritis.

METHODS

Male DBA/1 mice with collagen-induced arthritis were treated with antibodies against murine TNF alpha and IL-1 alpha/beta at different time points of the disease. IL-1 receptor antagonist (IL-1Ra) was administered using Alzet osmotic minipumps. The effect of anticytokine treatment was monitored by visual scoring. Histology and cytokine reverse transcription polymerase chain reaction (RT-PCR) analyses were performed at the end of the treatment period.

RESULTS

Anti-TNF alpha treatment showed efficacy shortly after onset of the disease, but had little effect on fully established CIA. Histologic analysis after early treatment revealed that anti-TNF alpha significantly reduced joint pathology, as determined by infiltration of inflammatory cells and cartilage damage. Anti-IL-1 alpha/beta treatment ameliorated both early and full-blown CIA. This clear suppression of established arthritis was confirmed by administration of high doses of IL-1Ra. Dose-response experiments showed that a continuous supply of 1 mg/day was needed for optimal suppression. Histologic analysis showed markedly reduced cartilage destruction both in the knee and the ankle joints. Autoradiography demonstrated full recovery of chondrocyte synthetic function of articular cartilage. In addition, we found that the IL-1 beta isoform plays a dominant role in established CIA. Profound suppression of CIA was observed with anti-IL-1 beta, although elimination of both IL-1 alpha and IL-1 beta still gave better protection. Analysis of messenger RNA with RT-PCR revealed that IL-1 beta was highly upregulated in synovium and cartilage at late stages of CIA, whereas anti-IL-1 beta treatment markedly reduced IL-1 beta message in the synovium.

CONCLUSION

The present study identified different TNF alpha/IL-1 dependencies in various stages of CIA and revealed that blocking of TNF alpha does not necessarily eliminate IL-1. Continuous, high doses of IL-1Ra are needed to block CIA.

Histochemical analysis of insulin-like growth factor-1 binding sites in mouse normal and experimentally induced arthritic articular cartilage

Insulin-like growth factor-1 (IGF-1) plays a key role in regulation of chondrocyte metabolism. We examined the localization of IGF-1 binding sites on chondrocytes in cartilage from normal and experimentally induced arthritic mouse knee joints. Cryostat sections from patellar cartilage were incubated either with IGF-1 receptor antibody or biotinylated IGF-1. Subsequently confocal laser scanning microscopy was applied to compare the two staining procedures qualitatively and quantitatively. This approach allowed detailed analysis of membrane-associated and intracellular staining. Using IGF-1 receptor antibody, IGF-1 receptors were found on the cell membrane of chondrocytes in the middle and deeper cartilage zones, whereas intracellular staining was highest in chondrocytes of superficial zones. After incubation with biotinylated IGF-1, distinct membrane staining was not present and fluorescence was localized homogeneously in the middle and deeper zones but not in superficial zones. In cartilage from inflamed knee joints staining with the use of IGF-1 receptor antibody did not change significantly, whereas a pronounced increase in staining was noted with biotinylated IGF-1 in chondrocytes of the middle and deeper zones of cartilage. It is concluded that the staining patterns obtained with the use of IGF-1 receptor antibody and biotinylated IGF-1 are remarkably different, suggesting that the latter also detects IGF-binding proteins. The results suggest that joint inflammation has no consistent effect on IGF-1 receptor expression but may induce a significant upregulation of IGF-binding proteins in chondrocytes of the middle and deeper zones of cartilage.

IL-1 has no direct role in the IGF-1 non-responsive state during experimentally induced arthritis in mouse knee joints

OBJECTIVE

To investigate the involvement of interleukin-1 (IL-1) in the induction or maintenance of the insulin-like growth factor 1 (IGF-1) non-responsive state of chondrocytes during experimental arthritis in mouse knee joints.

METHODS

To characterise IGF-1 nonresponsiveness during arthritis, we measured chondrocyte proteoglycan (PG) synthesis by assaying incorporation of 35S-sulphate into mouse patellar cartilage, obtained from knee joints with experimentally induced arthritis and normal knee joints, cultured with IGF-1. We investigated whether suppressive mediators produced by the arthritic synovium or chondrocytes abolished the IGF-1 stimulation of normal cartilage, and used IL-1 primed cartilage to mimic the arthritic in vivo state. Specific inflammatory mediators responsible for the maintenance of the suppressed IGF-1 response were sought. We measured IGF-1 responsiveness in normal and arthritic patellae cultured with antibodies against tumour necrosis factor (TNF) or IL-1 alpha/beta, with IL-1 receptor antagonist (IL-1ra), and with several inhibitors of proteolytic enzymes or reactive oxygen species, and analysed the role of IL-1 in the development of IGF-1 non-responsiveness by studying IGF-1 responses in cartilage treated with IL-1 antibodies in vivo, at the onset of arthritis.

RESULTS

Mediators from the surrounding tissue of both normal and arthritic cartilage suppressed chondrocyte IGF-1 responses. Priming the cartilage with IL-1 did not directly induce IGF-1 non-responsiveness, but enhanced the ability of suppressive mediators from synovium or chondrocytes to downregulate the IGF-1 responsive state. IL-1ra, IL-1 alpha/beta antibody, TNF antibody, or the inhibitors tested did not markedly improve the disturbed IGF-1 response, but treatment with anti-IL-1 at the onset of arthritis prevented the development of IGF-1 non-responsiveness.

CONCLUSION

IL-1 alone does not induce IGF-1 non-responsiveness and is not critical in the maintenance of this phenomenon. However, IL-1 does appear to be an important cofactor in the generation of the IGF-1 non-responsive state.

Chondrocyte IGF-1 receptor expression and responsiveness to IGF-1 stimulation in mouse articular cartilage during various phases of experimentally induced arthritis

OBJECTIVE

To examine the distribution of insulin like growth factor-1 (IGF-1) receptors and the biological response to IGF-1 stimulation in articular cartilage of normal mouse knee joints and arthritic joints taken at various stages of experimentally induced arthritis.

METHODS

In situ IGF-1 receptor expression and responsiveness to IGF-1 stimulation were examined in murine articular cartilage at different phases in two models of experimentally induced arthritis. IGF-1 receptor expression was visualised in joint sections with the use of anti-IGF-1 receptor antibodies and quantified by confocal laser scanning microscopy. Chondrocyte proteoglycan (PG) synthesis was measured by incorporation of 35S-sulphate.

RESULTS

In control cartilage, the majority of IGF-1 receptors were found on chondrocytes localised in the middle and deeper zones of the cartilage, whereas receptor expression in surface zone chondrocytes was very low. During culture of normal articular cartilage, IGF-1 was able to maintain chondrocyte PG synthesis at the in vivo level. Concurrently with the development of arthritis, cartilage lost its capacity to react to IGF-1, but IGF-1 stimulation recovered when the inflammatory response waned. Shortly after induction of arthritis, IGF-1 receptor expression initially declined, but it had returned to normal levels by day 1 and remained increased thereafter.

CONCLUSION

The distribution of IGF-1 receptor expression in the different zones of normal articular cartilage reflects IGF-1 stimulation and metabolic activity of chondrocytes in these layers. This correlation is disturbed in arthritic cartilage, suggesting inadequate or overruled signalling.

Role of interleukin-1, tumor necrosis factor alpha, and interleukin-6 in cartilage proteoglycan metabolism and destruction. Effect of in situ blocking in murine antigen- and zymosan-induced arthritis

OBJECTIVE

To determine the involvement of interleukin-1 (IL-1), tumor necrosis factor (TNF), and IL-6 in the cartilage pathology of murine antigen-induced arthritis (AIA) and zymosan-induced arthritis (ZIA).

METHODS

Arthritis was induced by intraarticular injection of zymosan in naive mice or by subcutaneous injection of methylated bovine serum albumin in sensitized animals. Mini-osmotic pumps releasing human recombinant IL-1 receptor antagonist (IL-1ra) protein were implanted intraperitoneally 2 days before arthritis induction, and neutralizing antibodies directed against murine IL-1 alpha, IL-1 beta, TNF alpha, or IL-6 were administered 1 day before. Proteoglycan (PG) synthesis and degradation were assessed in patellar cartilage.

RESULTS

Murine IL-1 alpha and IL-1 beta injected intraarticularly at doses of 0.1-100 ng suppressed chondrocyte PG synthesis. The highest dose of TNF tested (100 ng) decreased PG synthesis marginally. In contrast, the maximum dose of IL-6 (1 microgram) stimulated PG synthesis 2 days after injection. Treatment of AIA with neutralizing monoclonal antibodies against either TNF alpha or IL-6 did not reduce either the PG degradation or the suppression of its synthesis. However, treatment with anti-IL-1 (alpha + beta) polyclonal antibodies totally prevented PG suppression, although the initial breakdown of PG was unaffected. This effect was confirmed when IL-1ra was administered in high doses. Moreover, treatment of ZIA with anti-IL-1 (alpha + beta), but not with anti-TNF, resulted in normal PG synthesis, confirming the key role played by IL-1 in the inhibition of PG synthesis. Treatment of AIA with anti-IL-1 did not affect inflammation during the acute phase, but a significant reduction of ongoing inflammation was noted at day 7, and there was a marked reduction in the loss of cartilage PG.

CONCLUSION

The suppression of PG synthesis in both ZIA and AIA in mice is due to the combined local action of IL-1 (alpha + beta), and neither IL-6 nor TNF is involved. Moreover, the normalization of PG synthesis brought about by blocking of IL-1 ameliorates the cartilage damage associated with AIA.

Role of beta 2 integrins in the recruitment of phagocytic cells in joint inflammation in the rat

Adhesion molecules of the beta 2 family of integrins play an important role in adhesion and migration of leukocytes to inflammatory sites. Several in vivo studies indicate that not only monoclonal antibodies (mAbs) directed against the common beta subunit (CD18) but also to the individual alpha subunits (CD11a, CD11b) can effectively inhibit different types of inflammation. In this study we report that in the adjuvant arthritis (AA) alpha CD11a, alpha CD11b, or even alpha CD18 treatment could not prevent disease development. Moreover, we examined the same mAbs in an acute nonspecific inflammation at different sites in the rat. We found that pretreatment with alpha CD11a or alpha CD11b could significantly block a zymosan peritonitis, but appeared to have no effect on a locally induced joint or dermal inflammation. Interestingly, alpha CD18 treatment, which blocks the entire CD11/CD18 complex, was able to inhibit the influx of inflammatory cells in a peritonitis as well as in a joint and dermal inflammation. These data not only indicate that the type of joint inflammation determines which adhesion molecules play a role in transendothelial migration, but also that involvement of the beta 2 integrins is highly site specific.

Accelerated onset of collagen-induced arthritis by remote inflammation

Collagen-induced arthritis (CIA) in DBA-1 lac/J mice often has a low incidence, with gradual disease expression occurring over a broad time span (between days 35 and 70). The exact mechanisms underlying spontaneous expression are still poorly understood, although it is evident that some inflammatory cytokines like IL-1, tumour necrosis factor-alpha (TNF-alpha) and transforming growth factor-beta (TGF-beta) are potent accelerators. We have investigated whether we could trigger collagen type II-driven inflammation by: (i) enhancing anti-collagen type II (CII) antibodies, or (ii) a non-related inflammatory process. Male DBA-1 lac/J mice were immunized with 100 micrograms bovine type II collagen in Freund's complete adjuvant (FCA), resulting in a low disease expression at day 28. Addition of anti-CII antibodies slightly enhanced the expression of CIA. Zymosan (3 mg), given intraperitoneally, induced consistent expression of CIA after 1 week, whereas a retarded onset was noted with higher dosages. Local injection of a low dose of Zymosan (60 micrograms) in the knee joint, clearly potentiated the expression of CIA at that particular site. Higher concentrations not only elicited prolonged CIA expression at the injection site, but also induced marked CIA in the draining ankle joint. In contrast, intra-articular injection of Zymosan in nonimmunized DBAs or methylated bovine serum albumin (mBSA)/FCA-immunized controls only induced transient joint inflammation. The nature of the highly erosive CIA was confirmed histologically, and could easily be discriminated from the reversible changes induced with Zymosan. Our data indicate that latent autoimmune reactions may come to expression at the moment of non-specific inflammation, even at a remote site.

Responsiveness of articular cartilage from normal and inflamed mouse knee joints to various growth factors

OBJECTIVE

Disturbed anabolic signalling might contribute to the decreased chondrocyte proteoglycan (PG) synthesis during joint inflammation. Articular cartilage obtained from mouse knee joints with experimentally-induced arthritis exhibits a state of nonresponsiveness towards stimulation of chondrocyte PG synthesis by insulin-like growth factor-1 (IGF-1). Investigations were carried out on the role of other growth factors apart from IGF-1 on regulation of chondrocyte PG synthesis under pathological conditions, that is, during repair after IL-1 exposure as well as during early and later arthritis.

METHODS

Mouse patellae were obtained from normal knee joints and joints injected with IL-1 or zymosan. The patellae were cultured with basic fibroblast growth factor [bFGF], platelet-derived growth factor [PDGF], epidermal growth factor [EGF] or transforming growth factor beta [TGF beta] for 24 hours in the presence or absence of IGF-1. Chondrocyte PG synthesis was measured by 35S-sulphate incorporation.

RESULTS

In normal cartilage none of the tested growth factors elicited stimulatory effects on the chondrocyte PG synthesis as caused by IGF-1. EGF and TGF beta even caused significant inhibition of chondrocyte PG synthesis. Combination of bFGF or PDGF with IGF-1 exerted significant additional stimulation of the 35S-sulphate incorporation. IL-1 exposed cartilage displayed reactivity to IGF-1 as well as to the other growth factors similar to control cartilage. Cartilage obtained from joints with experimentally-induced arthritis exhibited a state of nonresponsiveness towards all individually tested growth factors as well as growth factor combinations.

CONCLUSION

Arthritis causes nonresponsiveness to stimulation of chondrocyte PG synthesis by the tested growth factors, which might be caused by a general receptor function defect.