Disease activity in rheumatoid arthritis is inversely related to cerebral TSPO binding assessed by [11C]PBR28 positron emission tomography.

Reumatoid Arthritis (RA) is an autoimmune disorder characterized by peripheral joint inflammation. Recently, an engagement of the brain immune system has been proposed. The aim with the current investigation was to study the glial cell activation marker translocator protein (TSPO) in a well characterized cohort of RA patients and to relate it to disease activity, peripheral markers of inflammation and autonomic activity. Fifteen RA patients and fifteen healthy controls matched for age, sex and TSPO genotype (rs6971) were included in the study. TSPO was measured using Positron emission tomography (PET) and the radioligand [11C]PBR28. The outcome measure was total distribution volume (VT) estimated using Logan graphical analysis, with grey matter (GM) as the primary region of interest. Additional regions of interest analyses as well as voxel-wise analyses were also performed. Clinical evaluation of disease activity, symptom assessments, serum analyses of cytokines and heart rate variability (HRV) analysis of 24 h ambulatory ECG were performed in all subjects. There were no statistically significant group differences in TSPO binding, either when using the primary outcome VT or when normalizing VT to the lateral occipital cortex (p > 0.05). RA patients had numerically lower VT values than healthy controls (Cohen's D for GM = -0.21). In the RA group, there was a strong negative correlation between [11C]PBR28 VT in GM and disease activity (DAS28)(r = -0.745, p = 0.002, corrected for rs6971 genotype). Higher serum levels of IFNγ and TNF-α were found in RA patients compared to controls (p < 0.05) and several measures of autonomic activity showed significant differences between RA and controls (p < 0.05). However, no associations between markers of systemic inflammation or autonomic activity and cerebral TSPO binding were found. In conclusion, no statistically significant group differences in TSPO binding as measured with [11C]PBR28 PET were detected. Within the RA group, lower cerebral TSPO binding was associated with higher disease activity, suggesting that cerebral TSPO expression may be related to disease modifying mechanisms in RA. In light of the earlier confirmed neuro-immune features of RA, these results warrant further investigations regarding neuro-immune joint-to-CNS signalling to open up for potentially new treatment strategies.

Why sickness hurts: A central mechanism for pain induced by peripheral inflammation.

Low-grade systemic inflammation has been implicated in chronic pain, as well as in comorbid diseases like depression and fatigue. We have previously shown that women's pain perception and regulation is more affected by systemic inflammation than that of men. Here we investigated the neural substrates underlying these effects using an fMRI paradigm previously employed in a clinical population. Fifty-one participants (29 women) were injected with 0.6ng/kg lipopolysaccharide (LPS) or saline to induce a peripheral inflammatory response. The subjects were then tested with a pressure pain fMRI paradigm designed to capture descending pain inhibitory activity 2h after injection, and blood was sampled for cytokine analysis. The subjects injected with LPS became more pain sensitive compared to the placebo group, and the heightened pain sensitivity was paralleled by decreased activity in the ventrolateral prefrontal cortex and the rostral anterior cingulate cortex (rACC) compared to placebo; areas involved in descending pain regulation. The LPS group also had higher activity in the anterior insular cortex, an area underpinning affective and interoceptive pain processing. Women displayed overall less pain-evoked rACC activity compared to men, which may have rendered women less resilient to immune provocation, possibly explaining sex differences in LPS-induced pain sensitivity. Our findings elucidate the pain-related brain circuits affected by experimental peripheral inflammation, strengthening the theoretical link between systemic inflammation and weakened pain regulation in chronic pain disorders. The results further suggest a possible mechanism underlying the female predominance in many chronic pain disorders.

Modality and sex differences in pain sensitivity during human endotoxemia.

Systemic inflammation can induce pain hypersensitivity in animal and human experimental models, and has been proposed to be central in clinical pain conditions. Women are overrepresented in many chronic pain conditions, but experimental studies on sex differences in pain regulation during systemic inflammation are still scarce. In two randomized and double blind placebo controlled experiments, we used low doses of lipopolysaccharide (LPS) as an experimental model of systemic inflammation. The first study employed 0.8ng/kg LPS in a within-subject design of 8 individuals (1 woman), and the second study 0.6ng/kg LPS in a between-subject design of 52 participants (29 women). We investigated the effect on (a) pressure, heat, and cold pain thresholds, (b) suprathreshold noxious heat and cold sensitivity, and (c) conditioned pain modulation (CPM), and differences between men and women. LPS induced significantly lower pressure pain thresholds as compared to placebo (mean change with the 0.8ng/kg dose being -64±30kPa P=.04; with the 0.6ng/kg dose -58±55kPa, P<.01, compared to before injection), whereas heat and cold pain thresholds remained unaffected (P's>.70). Suprathreshold noxious pain was not affected by LPS in men (P's⩾.15). However, LPS made women rated suprathreshold noxious heat stimuli as more painful (P=.01), and showed a tendency to rate noxious cold pain as more painful (P=.06) as compared to placebo. Furthermore, LPS impaired conditioned pain modulation, a measure of endogenous pain inhibition, but this effect was also restricted to women (P<.01, for men P=.27). Pain sensitivity correlated positively with plasma IL-6 and IL-8 levels. The results show that inflammation more strongly affects deep pain, rather than cutaneous pain, and suggest that women's pain perception and modulation is more sensitive to immune activation than men's.

Higher levels of interleukin IL-17 and antigen-specific IL-17 responses in pulmonary sarcoidosis patients with Löfgren's syndrome.

Sarcoidosis is a granulomatous disorder of unknown aetiology. The presence of Mycobacterium tuberculosis catalase-peroxidase (mKatG) in sarcoidosis tissue has been reported. T helper type 1 (Th1) responses against mKatG have previously been observed. However, little is known about interleukin (IL)-17 and Th17 responses in sarcoidosis. Here, we investigated the levels of IL-17 and frequencies of IL-17-producing cells responding to mKatG in sarcoidosis patients with different prognosis. Peripheral blood and bronchoalveolar lavage (BAL) cells were obtained from sarcoidosis patients with or without Löfgren's syndrome (often associated with spontaneous recovery), and also stratified according to human leucocyte antigen (HLA) type. Cells producing IL-17 and interferon (IFN)-γ after stimulation with mKatG were enumerated by enzyme-linked immunospot (ELISPOT). The level of IL-17 in the BAL fluid of sarcoidosis patients and healthy controls was measured by quantitative immuno-polymerase chain reaction (qIPCR). We also performed flow cytometry and immunohistochemistry for further characterization of IL-17 expression. Patients with Löfgren's syndrome had a higher frequency of IL-17-producing cells responding to mKatG in BAL fluid compared to patients without Löfgren's syndrome (P < 0·05). The HLA-DR3(+) sarcoidosis patients with Löfgren's syndrome (known to have a particularly good prognosis) also had a clearly higher level of IL-17 in BAL fluid compared to healthy controls and sarcoidosis patients without Löfgren's syndrome (P < 0·01) and (P < 0·05), respectively. No such difference between patient groups was observed with regard to IFN-γ and not with regard to either cytokine in peripheral blood. These findings suggest that IL-17-producing cells may be a useful biomarker for the prognosis of sarcoidosis and play a role in the spontaneous recovery typical of patients with Löfgren's syndrome.

Increased levels of nerve growth factor in the airways of patients with sarcoidosis.

OBJECTIVES: Nerve growth factor (NGF) is a potent neuronal growth factor with inflammatory properties that recently has been proposed to be of importance in airway pathology. A role for NGF in the inflammatory granulomatous lung disease sarcoidosis is not well elucidated. The aims of this study were to investigate the secreted levels of NGF in bronchoalveolar lavage fluid (BALF) from sarcoidosis patients compared with patients with resolved disease, patients with another granulomatous disease--chronic beryllium disease (CBD)--and healthy subjects and also to investigate the relationship between NGF levels and markers of inflammation. METHODS AND RESULTS: NGF levels in BALF from 56 patients with active sarcoidosis (22 with Löfgren's syndrome), nine subjects with resolved sarcoidosis, six patients with CBD, and 31 healthy subjects were compared. A 10-fold elevation of NGF levels was found in patients with active sarcoidosis compared with subjects with clinically resolved sarcoidosis, patients with CBD and healthy subjects. In sarcoidosis patients, positive correlations between concentrations of NGF and lymphocytes, eosinophils and interferon-gamma, interleukin (IL)-4, IL-10, IL-12 were found. CONCLUSIONS: We demonstrate that secreted levels of NGF are markedly enhanced in the airways in active pulmonary sarcoidosis. Furthermore, a relationship between NGF and pulmonary inflammation in sarcoidosis is supported.

Timing-dependent effects of restraint stress on eosinophilic airway inflammation in mice.

BACKGROUND: Chronic stress has been proposed to aggravate allergic inflammation, whereas acute stress may have functional beneficial effects. The aim of this study was to investigate the influence of timing of single short restraint stress (RST) in a model of eosinophilic airway inflammation. METHODS: The airways of ovalbumin (OVA)-sensitized mice were exposed to an intranasal OVA challenge. RST was applied in two different ways; either 2 h before (pre-stress) or after (post-stress) the OVA challenge, respectively, or as a combination of stress before and after (double-stress) the OVA challenge. One group of mice was also treated with metyrapone (ME) prior to a pre-stress challenge. The inflammatory cell response was evaluated in bronchoalveolar lavage fluid (BALF), lung and nasal tissue, as well as bone marrow. RESULT: RST applied prior to the OVA challenge (pre-stress) inhibited OVA-induced airway inflammation in BALF and lung tissue, and reduced nasal histopathology compared to unstressed mice. Given as post-stress or double-stress, RST did not affect the inflammation in BALF, lungs or nasal tissue. Pre-treatment with ME prevented the pre-challenge stress evoked decrease in inflammation in BALF and lungs. CONCLUSION: Effects of RST on eosinophilic airway inflammation appear to be strongly dependent on timing and, as could be judged from the ME inhibition pattern, also corticosterone dependent. Hypothalamic-pituitary-adrenal axis activation probably influences eosinophilic inflammation through specific sequences of compartmental activation and thereby timing effects are evident on cellular recruitment pattern during the allergic reaction.

Altered apoptosis in bronchoalveolar lavage lymphocytes after allergen exposure of atopic asthmatic subjects.

The increased number of lymphocytes in airways during an asthmatic response is believed to be the result of increased recruitment of these cells. However, it is possible that a decreased apoptotic rate could also contribute to the increased number. The aim of the present study was to investigate whether allergen airway provocation influences the apoptotic phenotype of lung and peripheral blood lymphocytes (PBL) in subjects with atopic asthma. Bronchoalveolar lavage (BAL) lymphocytes and PBL from 12 asthmatic subjects previously challenged with allergen (n = 7) or saline (n = 5) were exposed to the apoptotic stimulus tributyltin (TBT) in vitro and assayed for apoptosis. Airway allergen provocation resulted in decreased sensitivity of BAL lymphocytes to TBT-induced apoptosis, with 42.2% (range 33.9-62.5%) apoptotic cells before challenge versus 23.5% (range 15.3-42.4%) after challenge, while PBL were unaffected. The increased apoptosis resistance correlated with higher numbers of Bcl-2-expressing lymphocytes. Interestingly, baseline caspase-3-like activity was significantly elevated in viable BAL lymphocytes compared with viable PBL, and was unaltered by allergen exposure. In conclusion, allergen inhalation renders bronchoalveolar lavage lymphocytes more resistant to apoptosis while peripheral blood lymphocytes were not influenced at all, indicating that the apoptotic phenotype of airway lymphocytes may play a role in asthmatic inflammation.

Nerve growth factor is released by IL-1beta and induces hyperresponsiveness of the human isolated bronchus.

Nerve growth factor (NGF) is a neurotrophic factor essential for the development and survival of neurons, and is also an important mediator of inflammation. It is released by airway cells stimulated by interleukin (IL)-1beta. As IL-1beta induces airway hyperresponsiveness (AHR) to the tachykinin NK-1 receptor agonist [Sar9,Met(O2)11]-substance P in human isolated bronchi, the aim of this study was to determine whether IL-1beta was able to induce NGF release from isolated bronchi, and whether NGF might participate into IL-1beta-induced AHR. IL-1beta (10 ng x mL(-1); 21 degrees C; 15 h) increased the release of NGF from human isolated bronchi in vitro, and, in organ bath studies, the response of human bronchi to [Sar9,Met(O2)11]-substance P (0.1 microm). A significant correlation was found between these responses. AHR induced by IL-1beta was abolished by a blocking anti-human NGF antibody. Finally, NGF (1 ng x mL(-1); 37 degrees C; 0.5 h) by itself induced a significant increase in [Sar9,Met(O2)11]-substance P responsiveness. By contrast, it did not change the maximal contraction to acetylcholine. In conclusion, the present study clearly demonstrated that nerve growth factor may participate in the airway hyperresponsiveness induced by interleukin-1beta, which supports the neuro-immune cross-talk that may be active in the development of hyperresponsiveness in the human airways, and suggests nerve growth factor is active in the airways in asthma.

Nerve growth factor levels and localisation in human asthmatic bronchi.

Nerve growth factor (NGF) has recently been suggested to be an important mediator of inflammation. In support of this, serum levels of NGF have been shown to be enhanced in asthmatics. However, it has not yet been shown whether the levels of NGF are also altered locally in asthmatic airways, when compared with healthy subjects, and the localisation of potential sources of NGF in the human bronchus have not yet been described. The aim of the present study was to assess NGF levels in bronchoalveolar lavage fluid (BALF) from asthmatics and to compare them to those of control subjects. Furthermore, the authors wanted to localise potential sources of NGF in bronchial tissue, and to number NGF-immunopositive infiltrating cells in the bronchial submucosa. BALF and bronchial biopsies were obtained from seven control subjects and seven asthmatic patients by fibreoptic bronchoscopy. NGF protein levels were quantified by enzyme-linked immunosorbent assay in BALF. NGF localisation was examined by immunohistochemistry on bronchial biopsy sections. The asthmatics exhibited significantly enhanced NGF levels in BALF. Intense NGF-immunoreactivity was observed in bronchial epithelium, smooth muscle cells and infiltrating inflammatory cells in the submucosa, and to a lesser extent in the connective tissue. The asthmatics exhibited a higher number of NGF-immunoreactive infiltrating cells in the bronchial submucosa than control subjects. This study provides evidence that nerve growth factor is locally produced in the airways, and shows that this production is enhanced in asthmatics. These findings suggest that nerve growth factor is produced by both structural cells and infiltrating inflammatory cells in human bronchus in vivo, and the authors suggest that the increase in nerve growth factor protein in bronchoalveolar lavage fluid observed in asthmatic patients may originate both from structural cells, producing increased nerve growth factor levels in inflammatory conditons, and from the increase in nerve growth factor-immunopositive cells determined in the bronchial submucosa.

Nerve growth factor increases airway responses and decreases levels of exhaled nitric oxide during histamine challenge in an in vivo guinea-pig model.

There is a growing body of evidence supporting the idea that nerve growth factor (NGF) may be involved in the development of asthma-associated symptoms, such as airway hyper-responsiveness. Increased levels of NGF have recently been described in serum and in the airways of asthmatics. We have examined whether exhaled nitric oxide (NO) levels might be altered during the increased airway responses upon NGF treatment in guinea-pigs in vivo. Intravenous (i.v.) administration of histamine normally elicits a rapid peak in insufflation pressure (IP) and in exhaled NO, followed by a period of decreased concentrations of exhaled NO. Anaesthetized guinea-pigs were pre-treated intravenously with either saline, 4 or 80 ng x kg(-1) NGF 30 min before i.v. challenge with 16 microg x kg(-1) histamine. At 80 ng x kg(-1) NGF significantly enhanced the airway obstruction caused by histamine, whereas the peak acute increase in exhaled NO was not enhanced. Following the increase, came a rapid drop, an effect enforced in the NGF treated animals. Subsequently, the time to return to 90% of resting exhaled NO was increased, from 12 min in saline-treated animals to 48 min in NGF-treated animals. Our data confirm that NGF can enhance airway responses to histamine. Moreover, our study shows a decrease in exhaled NO following a histamine challenge, an effect enhanced by NGF. A reduced ability to release exhaled NO may be a mechanism for increased airway responses during elevated NGF levels. The interaction between NGF and airway NO formation, and its relation to airway responses, merit further investigation.