Mesenchymal stem cell therapy in proteoglycan induced arthritis.

OBJECTIVES: To explore the immunosuppressive effect and mechanism of action of intraperitoneal (ip) and intra-articular (ia) mesenchymal stem cell (MSC) injection in proteoglycan induced arthritis (PGIA). METHODS: MSC were administered ip or ia after establishment of arthritis. We used serial bioluminescence imaging (BLI) to trace luciferase-transfected MSC. Mice were sacrificed at different time points to examine immunomodulatory changes in blood and secondary lymphoid organs. RESULTS: Both ip and local ia MSC injection resulted in a beneficial clinical and histological effect on established PGIA. BLI showed that MSC ip and ia in arthritic mice are largely retained for several weeks in the peritoneal cavity or injected joint respectively, without signs of migration. Following MSC treatment pathogenic PG-specific IgG2a antibodies in serum decreased. The Th2 cytokine IL-4 was only upregulated in PG-stimulated lymphocytes from spleens in ip treated mice and in lymphocytes from draining lymph nodes in ia treated mice. An increase in production of IL-10 was seen with equal distribution. Although IFN-γ was also elevated, the IFN-γ/IL-4 ratio in MSC treated mice was opposite to the ratio in (untreated) active PGIA. CONCLUSIONS: MSC treatment, both ip and ia, suppresses PGIA, a non-collagen induced arthritis model. MSC are largely retained for weeks in the injection region. MSC treatment induced at the region of injection a deviation of PG-specific immune responses, suggesting a more regulatory phenotype with production of IL-4 and IL-10, but also of IFN-γ, and a systemic decrease of pathogenic PG-specific IgG2a antibodies. These findings underpin the potential of MSC treatment in resistant arthritis.

Mutations in MVK, encoding mevalonate kinase, cause hyperimmunoglobulinaemia D and periodic fever syndrome.

Hyperimmunoglobulinaemia D and periodic fever syndrome (HIDS; MIM 260920) is an autosomal recessive disorder characterized by recurrent episodes of fever associated with lymphadenopathy, arthralgia, gastrointestinal dismay and skin rash. Diagnostic hallmark of HIDS is a constitutively elevated level of serum immunoglobulin D (IgD), although patients have been reported with normal IgD levels. To determine the underlying defect in HIDS, we analysed urine of several patients and discovered increased concentrations of mevalonic acid during severe episodes of fever, but not between crises. Subsequent analysis of cells from four unrelated HIDS patients revealed reduced activities of mevalonate kinase (MK; encoded by the gene MVK), a key enzyme of isoprenoid biosynthesis. Sequence analysis of MVK cDNA from the patients identified three different mutations, one of which was common to all patients. Expression of the mutant cDNAs in Escherichia coli showed that all three mutations affect the activity of the encoded proteins. Moreover, immunoblot analysis demonstrated a deficiency of MK protein in patient fibroblasts, indicating a protein-destabilizing effect of the mutations.

Transition of rheumatologic care, from teenager to adult: which health assessment questionnaire can be best used?

OBJECTIVES: Transition of care for adolescents includes a transfer from paediatric to adult health care. This requires a transfer of specific measurements, which evaluate disease profiles such as functional ability. One of the most common measurements is the Health Assessment Questionnaire (HAQ). METHODS: Results of the Childhood HAQ (CHAQ) and HAQ were compared among adolescents diagnosed with rheumatic diseases involving the musculoskeletal system. All adolescents had recently dealt with or would in the near future be dealing with transition. RESULTS: Overall results of both questionnaires were comparable; intra-class correlation for consistency (ICC) was 0.95 (95% confidence interval 0.93-0.97). For a smooth transfer from CHAQ to HAQ, both correlation and agreement are required. Agreement between both questionnaires was not found. Described by limits of agreement, results of HAQ can differ from CHAQ as much as 0.95. CONCLUSIONS: Despite strong correlations for consistency, lack of agreement was found in the results of CHAQ and HAQ. If correlation persists over time, this study suggests evaluating both the childhood and adult version of the HAQ during the transition period. When transfer into adulthood is completed, comparison to earlier tests at younger age is available and reliable.

Current educational status of paediatric rheumatology in Europe: the results of PReS survey.

OBJECTIVES: To understand the status of education and problems in paediatric rheumatology practice in Europe, through a survey. METHODS: A 26-item questionnaire was conducted during the 14th Congress of the Paediatric Rheumatology European Society in Istanbul, 2007. Physicians who were practicing or studying within the field of paediatric rheumatology for at least one year were included in the survey. RESULTS: One hundred and twenty eight physicians, 79 paediatric rheumatologists (including 5 paediatric immunologists and 10 paediatric nephrologists), 34 paediatric rheumatology fellows and 15 adult rheumatologists completed the survey. The physicians were from: Europe 95 (81.9%), South America 12 (10.4%), Middle East 5 (4.3%), Asia 2 (1.7%), Africa 2 (1.7%). The duration of training for paediatric rheumatology ranged between 1-5 years (mean: 3.12+/-1.11). Sixty physicians scored their education as unsatisfactory and among those, 48 physicians were from Europe. Physicians reported good skills in the following items; intraarticular injections (83.3%); soft tissue injections (47.6%); evaluation of radiographs (67.5%); whereas competence in the evaluation of computed tomography/magnetic resonance imaging (30.5%); and musculoskeletal sonography (16.7%) was much lower. A need for improved basic science and rotations among relevant fields were specifically expressed. CONCLUSION: Being a relatively new speciality in the realm of paediatrics, paediatric rheumatology education at the European level needs to be further discussed, revised and uniformed.

Bacille-Calmette-Guerin vaccination and the development of allergic disease in children: a randomized, prospective, single-blind study.

BACKGROUND: The increase in the prevalence of allergic diseases in countries with a so-called western lifestyle may be due to a decrease in exposure to infectious agents in early life. OBJECTIVE: To establish the effect of Bacille-Calmette-Guerin (BCG) vaccination in 6-week-old high-risk infants in a prospective single-blind, randomized, placebo-controlled trial on the prevalence of allergic disease at the age of 4 and 18 months. METHODS: Subjects were 121 predominantly Caucasian high-risk newborns, having either a mother, or both a father and at least one sibling with past or present allergic disease. BCG or placebo was administered at the age of 6 weeks, and repeated once when both a post-vaccination scar and a positive TB skin test were absent at the age of 4 months. RESULTS: At the age of 18 months, the prevalence of allergic disease was not significantly different between the two groups. A trend towards less eczema (P=0.07) and significantly less use of medication for eczema was shown in the BCG group compared with the placebo group (P=0.04). CONCLUSION: A single (or once repeated) BCG vaccination in 6-week-old high-risk Caucasian infants was not associated with a 50% reduction in the prevalence of allergic disease. However, there could be a smaller beneficial effect of BCG, especially because a trend towards less eczema and significantly less use of medication for eczema was shown. For definite proof, a larger study should be carried out.

Calcinosis in juvenile dermatomyositis: a possible role for the vitamin K-dependent protein matrix Gla protein.

OBJECTIVES: The aims of the present study were to investigate whether the calcification inhibitor matrix Gla protein (MGP) is expressed in muscle biopsies of patients with juvenile dermatomyositis (JDM), and whether different forms of MGP are differentially expressed in JDM patients with and without subcutaneous calcifications. METHODS: Muscle tissue from six JDM patients (three without calcinosis, two with calcinosis and one recently diagnosed patient), four patients with muscular dystrophy, three patients with IBM and five normal histological control subjects was used for immunohistochemistry staining using novel antibodies to different conformations of MGP. RESULTS: In the JDM patients, all forms of MGP [non-carboxylated MGP (ucMGP), carboxylated MGP (cMGP), non-phosphorylated MGP (serMGP) and phosphorylated MGP (pserMGP)] were more intensely stained in the perifascicular compared with the central muscle fibres. In addition, these MGP species were demonstrated in the pathological muscle fibres of IBM and dystrophy patients, but hardly in normal histological muscle tissue. In JDM patients with calcifications, only pserMGP was increased compared with those without calcifications. All forms of MGP were also found in various staining intensities in the microvasculature and macrophages of normal histological and disease biopsies. CONCLUSIONS: MGP was expressed at the site of muscle damage in JDM patients as well as in patients with muscular dystrophy and IBM. The difference in staining intensity of pserMGP appeared to distinguish between JDM patients with and without calcifications, whereas cMGP, the other functional form, was equally expressed.

Extremes in vitamin K status of bone are related to bone ultrasound properties in children with juvenile idiopathic arthritis.

OBJECTIVE: Osteopenia is a common complication of juvenile idiopathic arthritis (JIA). In adults, low bone density and increased fracture risk are associated with low vitamin K status of bone. The vitamin K-dependent protein osteocalcin plays an important role in bone metabolism. Its activity depends upon post-translational carboxylation in which vitamin K is an essential co-factor. Hence, vitamin K deficiency leads to under-carboxylated (i.e., inactive) osteocalcin (ucOC). Little is known about the vitamin K status and bone health in children with juvenile idiopathic arthritis (JIA). We studied the vitamin K status of bone and its association with bone mass properties in children with JIA compared to healthy children. METHODS: We performed a cross sectional study in 55 children with JIA and 54 healthy controls between 6-18 years of age. Bone markers, ultrasound bone mass properties and vitamin K status of bone were determined. RESULTS: Overall, no differences in vitamin K status of bone were found between the study groups. Among children with JIA, a high ratio of ucOC/cOC indicating low vitamin K status was associated with low bone ultrasound parameters, whereas children with a high vitamin K status had markedly higher bone properties. This association was independent of physical activity, age, gender and BMI. CONCLUSION: These results suggest that vitamin K may be one of multiple risk factors for low bone mass in children with JIA, in addition to other recognized determinants of bone mass. The question remains whether JIA patients would benefit from increased dietary vitamin K intake.

Exercise therapy in juvenile idiopathic arthritis.

BACKGROUND: Exercise therapy is considered an important component of the treatment of arthritis. The efficacy of exercise therapy has been reviewed in adults with rheumatoid arthritis but not in children with juvenile idiopathic arthritis (JIA). OBJECTIVES: To assess the effects of exercise therapy on functional ability, quality of life and aerobic capacity in children with JIA. SEARCH STRATEGY: The Cochrane Central Register of Controlled Trials (CENTRAL), Cochrane Database of Systematic Reviews (The Cochrane Library), MEDLINE (January 1966 to April 2007), CINAHL (January 1982 to April 2007), EMBASE (January 1966 to October 2007), PEDro (January 1966 to October 2007), SportDiscus (January 1966 to October 2007), Google Scholar (to October 2007), AMED (Allied and Alternative Medicine) (January 1985 to October 2007), Health Technologies Assessment database (January 1988 to October 2007), ISI Web Science Index to Scientific and Technical Proceedings (January 1966 to October 2007) and the Chartered Society of Physiotherapy website (http://www.cps.uk.org) were searched and references tracked. SELECTION CRITERIA: Randomised controlled trials (RCTs) of exercise treatment in JIA. DATA COLLECTION AND ANALYSIS: Potentially relevant references were evaluated and all data were extracted by two review authors working independently. MAIN RESULTS: Three out of 16 identified studies met the inclusion criteria, with a total of 212 participants. All the included studies fulfilled at least seven of 10 methodological criteria. The outcome data of the following measures were homogenous and were pooled in a meta-analysis: functional ability (n = 198; WMD -0.07, 95% CI -0.22 to 0.08), quality of life (CHQ-PhS: n = 115; WMD -3.96, 95% CI -8.91 to 1.00) and aerobic capacity (n = 124; WMD 0.04, 95% CI -0.11 to 0.19). The results suggest that the outcome measures all favoured the exercise therapy but none were statistically significant. None of the studies reported negative effects of the exercise therapy. AUTHORS' CONCLUSIONS: Overall, based on 'silver-level' evidence (www.cochranemsk.org) there was no clinically important or statistically significant evidence that exercise therapy can improve functional ability, quality of life, aerobic capacity or pain. The low number of available RCTs limits the generalisability. The included and excluded studies were all consistent about the adverse effects of exercise therapy; no short-term detrimental effects of exercise therapy were found in any study. Both included and excluded studies showed that exercise does not exacerbate arthritis. The large heterogeneity in outcome measures, as seen in this review, emphasises the need for a standardised assessment or a core set of functional and physical outcome measurements suited for health research to generate evidence about the possible benefits of exercise therapy for patients with JIA. Although the short-term effects look promising, the long-term effect of exercise therapy remains unclear.

Differential processing of proenkephalin-A by human peripheral blood monocytes and T lymphocytes.

Human peripheral blood mononuclear cells are analyzed for preproenkephalin gene expression and peptide processing. Met-enkephalin immunoreactivity as detected with a specific antiserum is found in the cytoplasm of monocytes but not in T lymphocytes. Secretion of met-enkephalin was analyzed with an RIA that is specific for the met-enkephalin pentapeptide. Unfractionated PBMC spontaneously released 40 pg/ml met-enkephalin and this increased two- to fourfold after stimulation with PHA. Lower levels (less than 100 pg/ml) of met-enkephalin were detected in supernatants from purified T cells that were activated with PHA and IL-2. In contrast, stimulation of purified monocytes with LPS or PMA resulted in the release of up to 600 pg/ml of the processed peptide. To examine whether T cells can produce met-enkephalin precursor peptides, T cell conditioned media were treated with trypsin and carboxypeptidase-B, which is known to release met-enkephalin from the propeptide. This increased levels of met-enkephalin to 400 pg/ml, indicating that lymphocytes secrete the propeptide but do not process it to met-enkephalin. The 1.4-kb preproenkephalin mRNA is detected in activated blood mononuclear cells and in purified monocytes and T cells. To determine whether monocytes or lymphocytes express met-enkephalin in vivo, lymphoid tissues were analyzed by immunohistochemistry. In human spleen tissue, positive cells were found in the red pulp but not in the follicles, which is also consistent with met-enkephalin expression in monocytes. In summary, these results show that human peripheral blood mononuclear cells express preproenkephalin mRNA and that monocytes, but not T cells, process the propeptide to metenkephalin.

Juvenile chronic arthritis: T cell reactivity to human HSP60 in patients with a favorable course of arthritis.

Synovial fluid and peripheral blood mononuclear cell proliferative responses to the 60-kD human heat shock protein (HSP60) were studied in 23 patients with juvenile chronic arthritis (JCA) and 7 non-JCA control patients. All patients showed active arthritis at the time of study. The patients were divided into two groups according to the presence (group A) or absence (group B) of T lymphocyte reactivity to human HSP60. We show that reactivity to human HSP60 is primarily, though not exclusively, occurring in patients with a remitting course of disease, i.e., the subgroup of HLA-B27 negative JCA patients with an oligoarticular onset. Immunohistochemical analysis of HSP expression in synovial membranes showed a significantly higher intensity of staining in JCA patients than in non-JCA controls. The results suggest that, in accordance with the earlier observation made in experimental models, T lymphocyte reactivity to human HSP60 in this subgroup of JCA patients may be part of T cell regulatory mechanisms that control the development of arthritis.

[The basic biomedical subjects are of undiminished importance in the training of medical doctors]. / De biomedische basisvakken zijn onverminderd van belang voor de artsopleiding.

The contemporary physician is not merely a professional who is trained in the recognition of clinical syndromes and the application of evidence-based medicine. A good understanding of the basic biomedical sciences is necessary to comprehend what is wrong with a patient and what form of treatment is the most appropriate, especially if a disease manifests itself in an unfamiliar way.

Incidence and hemodynamic characteristics of near-fainting in healthy 6- to 16-year old subjects.

OBJECTIVES: We studied the incidence and hemodynamic characteristics of near-fainting under orthostatic stress in healthy children and teenagers. BACKGROUND: Orthostatic stress testing is increasingly used to identify young subjects with unexplained syncope. However, the associated incidence of syncope and hemodynamic responses in normal young subjects are not well known. METHODS: Eighty-four healthy subjects 6 to 16 years old performed forced breathing, stand-up and 70 degrees tilt-up tests. An intravenous line to sample blood for biochemical assessment of sympathetic function was introduced between the stand-up and tilt-up tests. Finger arterial pressure was measured continuously. Left ventricular stroke volume was computed from the pressure pulsations. RESULTS: Sixteen of the 84 subjects were excluded because of technical problems. The incidence of a near-fainting response in the remaining 68 subjects was 10% (7 of 68) for the stand-up test and 40% (29 of 68) for the tilt-up test. Baseline parasympathetic and sympathetic activity of nonfainting and near-fainting subjects was not different. Near-fainting was characterized by attenuated systemic vasoconstriction and exaggerated tachycardia that occurred as early as 1 min after return to the upright position. On tilt-up, plasma adrenaline levels increased by a factor of 2, with slightly higher increments in the near-fainting subjects. CONCLUSIONS: Inadequate vasoconstriction is the common underlying mechanism of near-fainting in young subjects. The remarkably high incidence of near-fainting during the tilt-up test after intravascular instrumentation raises serious doubts about the utility of this procedure in evaluating syncope of unknown origin in young subjects.

Disturbed neuroendocrine-immune interactions in chronic fatigue syndrome.

The present study was designed to investigate the interaction between neuroendocrine mediators and the immune system in chronic fatigue syndrome (CFS). We examined the sensitivity of the immune system to the glucocorticoid agonist dexamethasone and the beta2-adrenergic agonist terbutaline in 15 adolescent girls with CFS and 14 age- and sex-matched controls. Dexamethasone inhibits T-cell proliferation in healthy controls and in CFS patients. However, the maximal effect of dexamethasone on T-cell proliferation is significantly reduced in CFS patients as compared with controls. The beta2-adrenergic receptor agonist terbutaline inhibits tumor necrosis factor-alpha production and enhances interleukin-10 production by monocytes. Our data demonstrate that the capacity of a beta2-adrenergic agonist to regulate the production of these two cytokines is also reduced in CFS patients. We did not observe differences in baseline or CRH-induced cortisol and ACTH between CFS patients and controls. Baseline noradrenaline was similar in CFS and controls, whereas baseline adrenaline levels were significantly higher in CFS patients. We conclude that CFS is accompanied by a relative resistance of the immune system to regulation by the neuroendocrine system. Based on these data, we suggest CFS should be viewed as a disease of deficient neuroendocrine-immune communication.

High nocturnal melatonin in adolescents with chronic fatigue syndrome.

Decreased quality of sleep is frequently reported by chronic fatigue syndrome (CFS) patients. The pineal hormone melatonin is involved in regulation of sleep. We analyzed the nocturnal rise in melatonin in 13 adolescent CFS patients and 15 healthy age-matched controls. Saliva samples were collected at hourly intervals between 1700 and 0200 h. Nocturnal saliva melatonin levels were significantly higher in CFS patients, compared with controls, at midnight, 0100 h, and 0200 h (P < 0.001). No differences were observed in timing of melatonin increase in saliva between patients and controls. Time of sleep onset and duration of sleep did not differ significantly between patients and controls. However, all CFS patients and only one of the controls in our study group reported unrefreshing sleep. Our data demonstrate that sleep problems in adolescents with CFS are associated with increased melatonin levels during the first part of the night. Based on these data, we suggest that there is no indication for melatonin supplementation in adolescents with CFS.

Organization of the mevalonate kinase (MVK) gene and identification of novel mutations causing mevalonic aciduria and hyperimmunoglobulinaemia D and periodic fever syndrome.

Mevalonic aciduria (MA) and hyperimmunoglobulinaemia D and periodic fever syndrome (HIDS) are two autosomal recessive inherited disorders both caused by a deficient activity of the enzyme mevalonate kinase (MK) resulting from mutations in the encoding MVK gene. Thus far, disease-causing mutations only could be detected by analysis of MVK cDNA. We now describe the genomic organization of the human MVK gene. It is 22 kb long and contains 11 exons of 46 to 837 bp and 10 introns of 379 bp to 4.2 kb. Three intron-exon boundaries were confirmed from natural splice variants, indicating the occurrence of exon skipping. Sequence analysis of 27 HIDS and MA patients confirmed all previously reported genotypes based on cDNA analysis and identified six novel nucleotide substitutions resulting in missense or nonsense mutations, providing new insights in the genotype/phenotype relation between HIDS and MA.

Flow cytometric determination of FcgammaRIIa (CD32) polymorphism.

A guanine to adenine point mutation results in an arginine (R) to histidine (H) substitution in FcgammaRIIa at residue 131 that strongly impacts receptor function. This FcgammaRIIa polymorphism is mostly typed by allele-specific polymerase chain reactions (PCR) or in functional assays, dependent on ligand binding. Both types of methods are laborious, time consuming, and not readily available in routine laboratories. We generated a panel of human antibodies against FcgammaRII, and one of them, MDE-9, selectively recognized the FcgammaRIIa-H131 allotype. MDE-9 was applicable to detect FcgammaRIIa-H131 in both flow cytometry and immunohistochemistry. MDE-9 was used to develop an FcgammaRIIa allotyping method based on flow cytometry. In a "single-tube assay", FITC-labeled MDE-9 (specific for FcgammaRIIa-H131) and Cy3-labeled mAb 41H16 (specific for FcgammaRIIa-R131) were added to 50 mul samples of whole blood. The results of flow cytometric FcgammaRIIa allotyping correlated completely with PCR genotyping. This novel allotyping assay should facilitate the screening of patients in a routine diagnostic setting. In addition, a combination of MDE-9 and 41H16 can be used in FcgammaRIIa-H/H131 homozygous individuals to detect FcgammaRIIa and FcgammaRIIb surface expression on monocytes. This is an important application of these antibodies because, to this day, no antibodies were available to specifically study the surface expression of FcgammaRIIb.

Stress induces increases in IL-6 production by leucocytes of patients with the chronic inflammatory disease juvenile rheumatoid arthritis: a putative role for alpha(1)-adrenergic receptors.

Juvenile rheumatoid arthritis (JRA) is characterized by chronic inflammation of the joints. In the present study we demonstrate that exposure of JRA patients to a noradrenergic stressor (cold pressor test) results in enhanced LPS-induced IL-6 production by peripheral blood cells of these patients. Healthy, age-matched controls had the same rise in norepinephrine, but do not respond with changes in IL-6 production after exposure to the cold pressor test. Moreover, PBMC of patients with JRA express mRNA encoding alpha(1)-adrenergic receptors (AR), predominantly of the alpha(1d)-AR subtype. In contrast, we could not detect mRNA encoding for alpha(1)-AR in PBMC of healthy controls. The results of this study suggest that expression of alpha(1)-AR mRNA in PBMC during chronic inflammation is associated with altered responses of the immune system to stress.

T helper 2 cytokines induce preproenkephalin mRNA expression and proenkephalin A in human peripheral blood mononuclear cells.

We investigated the regulatory influence of several cytokines on the expression of preproenkephalin (PPE) mRNA in human peripheral blood mononuclear cells (PBMC). By use of a quantitative reverse-transcriptase-polymerase chain reaction (RT-PCR), we demonstrate that the T helper 2 cytokines IL-4 and IL-10 are more potent in upregulating PPE mRNA expression in human PBMC than the T helper 1 cytokines IL-2 and gamma-IFN. In addition, TGF-beta is also an effective inducer of PPE mRNA. TGF-beta, IL-4 and IL-10 increase the cytoplasmatic concentration of met-enkephalin in PBMC. Secretion of met-enkephalin in the culture supernatant of IL-4- or IL-10-stimulated PBMC could not be observed, but proenkephalin A-derived met-enkephalin containing peptides could be demonstrated. IL-4 and IL-10 do not induce PPE mRNA via the same pathways. We could observe that PKA is involved in IL-4 mediated PPE mRNA induction, whereas IL-10 apparently uses another route.

Functional alpha 1-adrenergic receptors on leukocytes of patients with polyarticular juvenile rheumatoid arthritis.

During the last decade it has been shown that the central nervous system can influence the immune system. In healthy individuals, catecholamines can inhibit the production of pro-inflammatory cytokines like interleukin-6 (IL-6) and tumor necrosis factor alpha (TNF-alpha) via interaction with beta 2-adrenergic receptors. In contrast, we show here that catecholamines can stimulate the production of the interleukin-6 (IL-6) in children with the chronic inflammatory disease polyarticular juvenile rheumatoid arthritis (JRA). The induction of IL-6 is mediated by triggering of alpha 1-adrenergic receptors on peripheral blood leucocytes of the patients with polyarticular JRA. Functional alpha 1-adrenergic receptors are absent on leukocytes of normal donors and on leukocytes of patients with the oligoarticular form of the disease.

Role of endogenous pro-enkephalin A-derived peptides in human T cell proliferation and monocyte IL-6 production.

In this paper, we describe that met-enkephalin and/or enkephalin-containing intermediary peptides of the prohormone pro-enkephalin A are produced and secreted by human peripheral blood T cells and monocytes. The peptides are produced after stimulation with the mitogenic monoclonal antibodies anti-CD2.1/2.2 and anti-CD28. In monocytes, enkephalin synthesis was induced by stimulation with lipopolysaccharide. We demonstrate here that these immune cell-derived enkephalins play an important regulatory role in the immune response. By using an anti-sense oligonucleotide strategy we could block the production of enkephalins. Blockade of the production of met-enkephalin and enkephalin-containing intermediary peptides resulted in enhancement of the proliferative T cell response and inhibition of monocyte IL-6 secretion. In vitro reconstitution of the anti-sense treated cultures with synthetic met-enkephalin or the delta-type specific opioid receptor agonist deltorphin could reverse inhibition of monocyte IL-6 production, suggesting that endogenous enkephalins act via membrane opioid receptors. In contrast, addition of met-enkephalin or deltorphin to the anti-sense treated T cell cultures did not have any effect on T cell proliferation.