Adipose tissue: a regulator of inflammation

Gender-based dimorphic pattern for interleukin-1 receptor antagonist in type 2 diabetes mellitus

Adipose tissue secretes a variety of cytokines, some of which are increased in the serum of obese patients. The anti-inflammatory interleukin-1 receptor antagonist (IL-1Ra) is the most highly elevated known cytokine in human obesity, and its serum levels are strongly associated with the degree of insulin resistance in non-diabetic patients.

AIM

The present study examined serum levels of IL-1Ra in type 2 diabetic patients (T2DM) and their relationships with three other adipokines (leptin, interleukin-6 [IL-6], adiponectin). Their correlation with anthropometric and biochemical variables was examined, as well as their intraindividual fluctuations.

METHODS

Fifty T2DM patients, aged 58+/-13 years, were consecutively recruited among those electively hospitalized for a one-week intensive training course with our Diabetes Education Service. Anthropometric measurements and blood samples were taken after an overnight fast on admission (baseline) and after four days.

RESULTS

Mean serum levels of IL-1Ra and leptin, but not of IL-6 and adiponectin, were significantly higher in women than in men (P<0.0006), and this difference persisted after correction for body mass index (BMI) (P<0.0004). In addition, IL-1Ra and leptin were strongly correlated with the BMI (P<0.0004). By contrast, no significant correlations were observed between IL-1Ra and glucose-control parameters. Finally, all four adipokines exhibited wide interindividual variability, but with limited intraindividual fluctuations over the short time period.

CONCLUSION

IL-1Ra, leptin and adiponectin serum levels exhibit marked interindividual variation with high intraindividual consistency. A gender-based dimorphic pattern for IL-1Ra, independent of the degree of adiposity and glucose control, was also found.

Explant cultures of white adipose tissue

Obesity is characterized by increased adiposity of visceral and subcutaneous depots as well as other organs, including the vasculature. These fat depots secrete various hormone-like proteins implicated in metabolic homeostasis (e.g., adiponectin, resistin), the central control of appetite (e.g., leptin) and the increased production of cytokines. These molecules act either in a paracrine or endocrine manner, contributing to the metabolic and cardiovascular complications of obesity. Explant cultures of white adipose tissue are an important step in analyzing the secretory mechanisms of adipose tissue by preserving the physiological in vivo cross-talk between the various types of cells.

C-reactive protein in children with obstructive sleep apnea and the effects of treatment

OBJECTIVE

To evaluate C-reactive protein (CRP) concentration in children with OSA and to determine the effects of treatment for OSA on its serum concentration.

METHODS

Consecutive children with habitual snoring and symptoms suggestive of OSA were recruited. They completed a sleep apnea symptom questionnaire, underwent physical examination and an overnight polysomnography (PSG). Fasting serum CRP and lipid profile were taken after overnight PSG. OSA was diagnosed if obstructive apnea index (OAI)>1.

RESULTS

One hundred forty-one children with a median (IQR) age of 10.8 (8.5-12.8) years were recruited. There were 96 boys and the commonest presenting symptoms were nocturnal mouth breathing, prone sleeping position and poor attention at school. Forty-five children were found to have OSA and those with moderate disease (OAI>5) had significantly higher CRP levels compared to their non-OSA counterparts [1.3 (0.8-3.6) vs. 0.7 (0.2-2.0), P=0.01]. Stepwise linear multiple regression analysis indicated that OAI was independently associated with CRP (beta coefficient=0.013, P=0.001). Sixteen children underwent treatment and there was significant reduction in their serum CRP after intervention [pre vs. post-CRP, 1.3 (0.6-4.1) vs. 0.4 (0.2-1.3), P=0.033]. A significant correlation was also demonstrated between change in CRP and change in OAI (r=0.593, P=0.042) following treatment for OSA.

CONCLUSION

Children with OSA may have associated systemic inflammation as reflected by a raised CRP that decreased significantly following treatment.

Toxicogenetics and nutrigenetics: biomarkers in occupational medicine and litigation

Along with other 'omic' technologies, advances in nutritional genomics are likely to lead to increasing personalization in the area of nutrition, diet and health. The power of nutrients to modulate the toxicity of environmental pollutants and the importance of nutritional status in determining longer-term health outcomes may be of major benefit in occupational health and preventive medicine. Advances in metabolomics offer the promise of validating important intermediate and surrogate markers for use in medical monitoring.

Adipocyte-derived lipoprotein lipase induces macrophage activation and monocyte adhesion: role of fatty acids

OBJECTIVE

We evaluated the effect of adipocyte-derived lipoprotein lipase (LPL) on macrophage activation and monocyte adhesion and the role of fatty acids in these effects.

RESEARCH METHODS AND PROCEDURES

3T3-L1 adipocytes were incubated with heparin or insulin to induce LPL secretion; then adipocyte conditioned media (CM) were added to cultured J774 macrophages or human aortic endothelial cells (HAECs). Macrophage cytokine production and monocyte adhesion to HAECs were determined.

RESULTS

Incubation of macrophages with heparin- or insulin-treated adipocyte CM increased tumor necrosis factor alpha, interleukin-6, and nitric oxide production by these cells. LPL neutralization and heparinase treatment prevented these effects. Addition of active LPL or palmitate to cultured macrophages replicated these effects. Blockade of leptin also reduced the effect of insulin-treated adipocyte CM on macrophage inflammatory changes. Induction of macrophage cytokine secretion by leptin was prevented by LPL immunoneutralization. Finally, addition of CM of heparin- or insulin-treated adipocytes to HAECs stimulated monocyte adhesion to these cells, an effect that was abrogated by an anti-LPL antibody. This effect was reproduced by treating HAECs with active LPL or palmitate.

DISCUSSION

These results point to an effect of LPL-mediated lipolysis in macrophage activation and monocyte adhesion.

Effects of chronic exercise on cytokine production in white adipose tissue and skeletal muscle of rats

White adipose tissue (WAT) is a major source of production of cytokines involved in chronic diseases such as obesity, type 2 diabetes, and atherosclerosis. Long-term exercise has been proposed as a therapy to reduce chronic inflammation. We investigated here the influence of an intense exercise training (over 7 weeks) on several cytokine concentrations including interleukin 1 receptor antagonist (IL-1ra), IL-1beta, and IL-12 in serum, WAT, and skeletal muscle (SM) from non-obese rats. Two groups of 10 rats were investigated: one group was progressively trained (the two last weeks: 120min per day, 25m/min, 7% grade, 5 days per week) and the other age-matched group was used as a sedentary control. Compared to sedentary rats, weight gain was lower in the trained rats (P<0.01). In WAT, concentrations of IL-1ra, IL-1beta, and IL-12 were lower (P<0.001 for IL-1ra and IL-12, P<0.05 for IL-1beta) while they were higher in SM (P<0.01 for IL-1ra, P<0.001 for IL-1beta, P<0.05 for IL-12), and similar in serum. Significant correlations were noted between (i) body weight and WAT concentrations of IL-1ra, IL-1beta, and IL-12 (0.595, 0.450, and 0.481, respectively), (ii) body weight and IL-1beta concentration in SM (-0.526). We also observed significant negative correlations between WAT and SM concentrations of the three cytokines. We show here for the first time that intense exercise training with weight loss reduced concentrations of IL-1ra, IL-1beta, and IL-12 in WAT, while it increased them in SM. These results suggest that exercise could help reduce inflammation in WAT through mobilization of immune cells producing pro- and anti-inflammatory cytokines in SM.

The effect of infliximab on circulating levels of leptin, adiponectin and resistin in patients with inflammatory bowel disease

BACKGROUND

Tumour necrosis factor alpha is a critical mediator of inflammation-related altered metabolism in inflammatory bowel disease (IBD), possibly through its interaction with adipokines, which play an important role in IBD. Infliximab is a well established antitumour necrosis factor alpha treatment in IBD.

AIM AND METHODS

We studied serum levels of leptin, adiponectin and resistin in 20 IBD patients before and after infliximab treatment using commercially available enzyme-linked immunosorbent assays. The results were correlated with alterations of disease activity, BMI and C-reactive protein.

RESULTS

Infliximab induced clinical response or remission in 18 out of 20 treated IBD patients. Mean serum-leptin levels were 4.6+/-0.5 and 5.1+/-0.5 ng/ml (P=0.41), mean serum-adiponectin levels were 10513.9+/-1216.9 and 9653.5+/-1031.5 ng/ml (P=0.36) and mean serum-resistin levels were 26.3+/-4.1 and 13.9+/-1.4 ng/ml (P=0.004), before and after infliximab treatment, respectively. No significant correlation between the changes of BMI, C-reactive protein or the clinical indices of activity and alterations of the examined adipokines was found.

CONCLUSIONS

Serum levels of leptin and adiponectin had no significant alterations, whereas serum-resistin levels are significantly decreased after infliximab therapy in IBD patients, suggesting a possible proinflammatory status for resistin in IBD and a role as a marker of successful therapy.

Adipose tissue as an immunological organ: Toll-like receptors, C1q/TNFs and CTRPs

Adipose tissue has long been regarded as a mostly resting tissue that is dedicated solely to energy storage and release. However, in recent years, this view has changed dramatically following new insights into the metabolic and immunological functions of preadipocytes and adipocytes. There are several lines of evidence for the involvement of adipose tissue in innate and acquired immune responses. First, adipocytes are potent producers of proinflammatory cytokines, such as interleukin-6 and tumor necrosis factor (TNF), and chemokines. Furthermore, adipocytes secrete high amounts of adipokines, such as leptin, adiponectin and resistin, that regulate monocyte/macrophage function, and also secrete molecules associated with the innate immune system, such as the C1qTNF-related protein superfamily. Finally, preadipocytes and adipocytes express a broad spectrum of functional Toll-like receptors and the former can convert into macrophage-like cells. Collectively, these data clearly establish the role of adipose tissue as a new member of the immune system.

Interleukin1beta genetic polymorphisms interact with polyunsaturated fatty acids to modulate risk of the metabolic syndrome

Chronic inflammation has been identified as an important component of the metabolic syndrome (MetS). Therefore, environmental and genetic factors contributing to the variation of inflammatory responses could affect individuals' susceptibility to MetS. We investigated the association between common IL1beta genetic polymorphisms, inflammation, and the MetS, and the modulation of diet-related variables (i.e., erythrocyte membrane fatty acid composition) in a white U.S. population. IL1beta single nucleotide polymorphisms (SNP) (-1473G > C, -511G > A, -31T > C, 3966C > T, 6054G > A), clinical and biochemical measurements were characterized in a total of 1120 subjects (540 males and 580 females) participating in the Genetics of Lipid Lowering Drugs and Diet Network (GOLDN) Study. The 6054 G > A SNP was significantly associated with plasma C-reactive protein (P = 0.054), adiponectin (P = 0.021), and the prevalence of MetS (P = 0.004). Moreover, there was a significant interaction between the 6054G > A SNP and erythrocyte membrane (n-3) PUFA (P = 0.019). Among subjects with low (n-3) PUFA content (below the median), the 6054 G allele was associated with increased risk of the MetS (OR = 3.29, 95%CI = 1.49-7.26 for GG and OR = 1.95, 95%CI = 0.85-4.46 for GA, P < 0.001) compared with the AA genotype, but there were no significant genotype associations among subjects with high (n-3) PUFA content (above the median). Further analyses supported a significant haplotype global effect on the MetS (P = 0.017) among subjects with low (n-3) PUFA content. These results suggested that IL1beta genetic variants were associated with measures of chronic inflammation and the MetS risk, and that genetic influences were more evident among subjects with low (n-3) PUFA intake.

Serum concentration of visfatin in obese women

The aim of the present study was to determine serum concentrations of visfatin in obese women in comparison to normal-weight controls. Study subjects were 21 obese women without additional disease (age, 29.0+/-4.9 years; body mass index, 37.1+/-6.1 kg/m2) and 16 healthy, normal-weight women (age, 29.9+/-5.4 years; body mass index, 22.5+/-1.7 kg/m2). Body composition was measured by bioimpedance. Serum concentrations of visfatin were assayed with an enzyme-linked immunosorbent assay kit (Phoenix Pharmaceuticals, Burlingame, CA). Insulin was determined by radioimmunoassay and glucose by colorimetric method. Serum concentration of visfatin was significantly higher in obese women when compared to controls. Positive correlations between serum concentrations of visfatin and insulin in the obese group were found. In the control group, we observed positive correlations between serum concentrations of visfatin and glucose. In conclusion, the observed increase of visfatin in obesity may be a counterregulation preventing further glucose increase.

Is a model useful in exploring the catabolic mechanisms of weight loss after gastric bypass in humans?

PURPOSE OF REVIEW

In the USA, approximately 3% of adults are morbidly obese, in whom behavior modification and drug therapy is ineffective in inducing major weight loss. Surgery is their only reliable option. The Roux-en-Y gastric bypass accounts for 90% of all bariatric surgeries because it achieves the best weight loss results. Many studies describe weight loss and changes in metabolic blood parameters after Roux-en-Y gastric bypass. We compare recent human data with the findings in our rats to validate the versatility of using a Roux-en-Y gastric bypass rat model to explore the multifactorial molecular and physiological dimensions of weight loss and weight regain.

RECENT FINDINGS

Not only mechanical factors but also changes in gastrointestinal and adipose hormones and hypothalamic neuropeptides contribute to Roux-en-Y gastric bypass induced weight loss by promoting catabolic processes. Nevertheless, the exact mechanisms of weight loss remain unknown.

SUMMARY

To investigate these catabolic mechanisms we used our Roux-en-Y gastric bypass rat model in diet induced obese rats. We found clear morphometric, physiological and biochemical parallelisms between humans and our rats. It is likely that Roux-en-Y gastric bypass induces similar changes in hypothalamic neuropeptides which can only be studied using the rat model. It therefore provides a useful research tool for exploring and studying the development of adjuvant antiobesity therapies.

Cholecystosteatosis: an explanation for increased cholecystectomy rates

INTRODUCTION

Over the past decade, obesity has become epidemic, and the number of cholecystectomies as well as the percentage with acalculous cholecystitis have increased. We have recently reported that congenitally obese mice and lean mice fed a high fat diet have increased gallbladder wall lipids and poor gallbladder emptying. Therefore, we tested the hypothesis that compared to patients with a normal gallbladder, patients with both acalculous and calculous cholecystitis would have increased gallbladder wall fat.

METHODS

Sixteen patients who underwent cholecystectomy for acalculous cholecystitis were identified. Sixteen nondiseased controls who underwent incidental cholecystectomy during surgery for liver or pancreatic disease and 16 diseased controls whose gallbladder was removed for chronic calculous cholecystitis were chosen to match the acalculous patients for gender and Body Mass Index. Pathology specimens were reviewed in a blinded fashion for gallbladder wall fat, thickness, and inflammation.

RESULTS

Acalculous cholecystitis patients were younger (p < 0.01) than nondiseased or diseased controls. Gallbladder wall fat was significantly increased (p < 0.02) in the acalculous and calculous cholecystitis patients compared to the nondiseased controls. Gallbladder wall thickness (p < 0.02) and inflammatory score (p < 0.01) were highest in the calculous cholecystitis patients.

CONCLUSIONS

These data suggest that compared to nondiseased controls, (1) patients with acalculous cholecystitis are younger and have increased gallbladder fat and (2) patients with calculous cholecystitis have increased gallbladder fat and inflammation. We conclude that increased gallbladder fat may lead to poor gallbladder emptying and biliary symptoms. Thus, cholecystosteatosis may explain, in part, the increased need for cholecystectomy and the higher percentage of these patients with acalculous cholecystitis.

Combined effects of rosiglitazone and conjugated linoleic acid on adiposity, insulin sensitivity, and hepatic steatosis in high-fat-fed mice

Dysfunctional cross talk between adipose tissue and liver tissue results in metabolic and inflammatory disorders. As an insulin sensitizer, rosiglitazone (Rosi) improves insulin resistance yet causes increased adipose mass and weight gain in mice and humans. Conjugated linoleic acid (CLA) reduces adipose mass and body weight gain but induces hepatic steatosis in mice. We examined the combined effects of Rosi and CLA on adiposity, insulin sensitivity, and hepatic steatosis in high-fat-fed male C57Bl/6 mice. CLA alone suppressed weight gain and adipose mass but caused hepatic steatosis. Addition of Rosi attenuated CLA-induced insulin resistance and dysregulation of adipocytokines. In adipose, CLA significantly suppressed lipoprotein lipase and fatty acid translocase (FAT/CD36) mRNA, suggesting inhibition of fatty acid uptake into adipose; addition of Rosi completely rescued this effect. In addition, CLA alone increased markers of macrophage infiltration, F4/80, and CD68 mRNA levels, without inducing TNF-alpha in epididymal adipose tissue. The ratio of Bax to Bcl2, a marker of apoptosis, was significantly increased in adipose of the CLA-alone group and was partially prevented by treatment of Rosi. Immunohistochemistry of F4/80 demonstrates a proinflammatory response induced by CLA in epididymal adipose. In the liver, CLA alone induced microsteatotic liver but surprisingly increased the rate of very-low-density lipoprotein-triglyceride production without inducing inflammatory mediator-TNF-alpha and markers of macrophage infiltration. These changes were accompanied by significantly increased mRNA levels of stearoyl-CoA desaturase, FAT/CD36, and fatty acid synthase. The combined administration of CLA and Rosi reduced hepatic liver triglyceride content as well as lipogenic gene expression compared with CLA alone. In summary, dietary CLA prevented weight gain in Rosi-treated mice without attenuating the beneficial effects of Rosi on insulin sensitivity. Rosi ameliorated CLA-induced lipodystrophic disorders that occurred in parallel with rescued expression of adipocytokine and adipocytes-abundant genes.

Age, Gene/Environment Susceptibility-Reykjavik Study: multidisciplinary applied phenomics

In anticipation of the sequencing of the human genome and description of the human proteome, the Age, Gene/Environment Susceptibility-Reykjavik Study (AGES-Reykjavik) was initiated in 2002. AGES-Reykjavik was designed to examine risk factors, including genetic susceptibility and gene/environment interaction, in relation to disease and disability in old age. The study is multidisciplinary, providing detailed phenotypes related to the cardiovascular, neurocognitive (including sensory), and musculoskeletal systems, and to body composition and metabolic regulation. Relevant quantitative traits, subclinical indicators of disease, and medical diagnoses are identified by using biomarkers, imaging, and other physiologic indicators. The AGES-Reykjavik sample is drawn from an established population-based cohort, the Reykjavik Study. This cohort of men and women born between 1907 and 1935 has been followed in Iceland since 1967 by the Icelandic Heart Association. The AGES-Reykjavik cohort, with cardiovascular risk factor assessments earlier in life and detailed late-life phenotypes of quantitative traits, will create a comprehensive study of aging nested in a relatively genetically homogeneous older population. This approach should facilitate identification of genetic factors that contribute to healthy aging as well as the chronic conditions common in old age.

Body mass index and mortality in patients with idiopathic pulmonary fibrosis

BACKGROUND

To examine the relationship between body mass index (BMI) and mortality in patients with idiopathic pulmonary fibrosis (IPF).

METHODS

We studied a cohort of patients with IPF who were seen at the Mayo Clinic Rochester from 1994 through 1996. These patients met the current consensus definition of IPF. We excluded patients who had received prior treatment for IPF, had no follow-up data, or had no pulmonary function results available at the index visit.

RESULTS

Of the 197 patients fulfilling the inclusion criteria, the mean (+/- SD) age was 71.4 +/- 8.9 years, 137 patients (70%) were men, and the mean BMI was 28.2 +/- 4.6. These patients were categorized by BMI into the following three groups: < 25; 25 to 30; and >/= 30. There were 46 patients (23%) with a BMI of < 25 who had a median survival time of 3.6 years (1-year survival rate, 76% [95% confidence interval (CI), 65 to 90%]; 3-year survival rate, 54% [95% CI, 41 to 70%]). The second group consisted of 85 patients (43%) with a BMI between 25 and 30 who had a median survival time of 3.8 years (1-year survival rate, 84% [95% CI, 76 to 92%]; 3-year survival rate, 58% [95% CI, 48 to 70%]). The final group consisted of 66 patients (34%) with a BMI of >/= 30 and who had a median survival time of 5.8 years (1-year survival rate, 91% [95% CI, 84 to 98%]; 3-year survival rate, 69% [95% CI, 58 to 81%]). Using a proportional hazards regression model, survival was significantly associated with BMI (hazard ratio, 0.93 for each 1-U increase in BMI; 95% CI, 0.89 to 0.97; p = 0.002) with increased BMI being associated with better survival.

CONCLUSION

Higher BMI was associated with better survival in patients with IPF.

Nonalcoholic fatty pancreas disease

BACKGROUND

Obesity leads to fat infiltration of multiple organs including the heart, kidneys, and liver. Under conditions of oxidative stress, fat-derived cytokines are released locally and result in an inflammatory process and organ dysfunction. In the liver, fat infiltration has been termed nonalcoholic fatty liver disease, which may lead to nonalcoholic steatohepatitis. No data are available, however, on the influence of obesity on pancreatic fat and cytokines, and nonalcoholic fatty pancreas disease (NAFPD) has not been described. Therefore, we designed a study to determine whether obesity is associated with increased pancreatic fat and cytokines.

MATERIALS AND METHODS

Thirty C57BL/6J lean control and 30 leptin-deficient obese female mice were fed a 15% fat diet for 4 weeks. At 12 weeks of age all animals underwent total pancreatectomy. Pancreata from each strain were pooled for measurement of a) wet and dry weight, b) histologic presence of fat, c) triglycerides, free fatty acids (FFAs), cholesterol, phospholipids, and total fat, and d) interleukin (IL)-1beta and tumor necrosis factor-alpha (TNF-alpha). Data were analyzed by Student's t test and Fisher's exact test.

RESULTS

Pancreata from obese mice were heavier (p<0.05) and had more fat histologically (p<0.05). Pancreata from obese mice had more triglycerides, FFAs, cholesterol, and total fat (p<0.05). Triglycerides represented 11% of pancreatic fat in lean mice compared with 67% of pancreatic fat in obese mice (p<0.01). Cytokines IL-1beta and TNF-alpha also were elevated in the pancreata of obese mice (p<0.05).

CONCLUSIONS

These data suggest that obese mice have 1) heavier pancreata, 2) more pancreatic fat, especially triglycerides and FFAs, and 3) increased cytokines. We conclude that obesity leads to nonalcoholic fatty pancreatic disease.

Adiponectin and leptin: potential tools in the differential diagnosis of pediatric diabetes?

The incidence of type 1 and type 2 diabetes mellitus in the pediatric population has increased over the past decade. The practitioner is often faced with the challenge of differentiating between type 1 and type 2 diabetes at the time of initial diagnosis because of the overlap of clinical and laboratory characteristics between these two entities. Adipokines are proteins secreted by the adipose tissue. Leptin and adiponectin are two adipokines that have been extensively studied in vitro, in animal studies, and in human subjects with type 1 and type 2 diabetes. Leptin and adiponectin play a significant role in the regulation of lipid and carbohydrate metabolism. Adiponectin increases insulin sensitivity in both the liver and skeletal muscle. Leptin decreases appetite, increases energy expenditure, suppresses insulin synthesis and secretion and increases insulin sensitivity. Changes in the secretion or sensitivity to leptin and adiponectin may contribute to the development of type 1 and type 2 diabetes. Adiponectin is higher in adult and pediatric patients with type 1 diabetes compared to those with type 2 diabetes. Data regarding leptin levels are contradictory. Most studies report decreased serum leptin at the time of diagnosis in type 1 diabetes compared to type 2 diabetes subjects and non-diabetic controls. This paper will review basic research and clinical evidence supporting the role of adiponectin and leptin in the development of type 1 and type 2 diabetes and discuss their potential use as tools in the differential diagnosis of pediatric diabetes.

Increased expression of the adipokine genes resistin and fasting-induced adipose factor in hypoxic/ischaemic mouse brain

Adipose tissue is the primary source of the adipokines resistin and fasting-induced adipose factor (FIAF). We reported that the brain is also a site of adipokine expression, although their function there is unknown. Peripheral resistin and fasting-induced adipose factor are reported to be inflammatory markers, and we hypothesized that they would be induced in the brain by hypoxia/ischaemia. We show that neonatal hypoxia/ischaemia rapidly increased fiaf mRNA in the injured cortex and hippocampus at 2 and 7 days after hypoxia/ischaemia. In contrast, resistin (retn) mRNA was increased in the cortex only at 21 days after hypoxia/ischaemia. As a lipopolysaccharide-induced inflammatory response did not increase brain fiaf and retn mRNA levels, we conclude that brain injury may be responsible for the novel hypoxia/ischaemia-induced changes in adipokine gene expression. In summary, our results indicate that brain injury, or an inflammatory stimulus, regulates the central expression of two genes normally considered to be adipose tissue-specific. These observations add to our previous evidence that the brain is an important site of adipokine gene expression.

The role of leptin in innate and adaptive immune responses

Leptin is produced primarily by adipocytes and functions in a feedback loop regulating body weight. Leptin deficiency results in severe obesity and a variety of endocrine abnormalities in animals and humans. Several studies indicated that leptin plays an important role in immune responses. It exerts protective anti-inflammatory effects in models of acute inflammation and during activation of innate immune responses. In contrast, leptin stimulates T lymphocyte responses, thus having rather a proinflammatory role in experimental models of autoimmune diseases. Clinical studies have so far yielded inconsistent results, suggesting a rather complex role for leptin in immune-mediated inflammatory conditions in humans.