Background-Obesity is associated with chronic inflammation, which includes increased macrophage accumulation in adipose tissue (AT) and upregulation of chemokines and cytokines. T cells also play important roles in chronic inflammatory diseases such as atherosclerosis but have not been well studied in obesity. Methods and Results-Flow cytometric analysis showed higher numbers of T cells and macrophages in AT of diet-induced obese insulin-resistant male mice than in lean mice and obese females (PϽ0.05). RNase protection assay, ELISA, and flow cytometry indicated gender-dependent upregulation of mRNA and protein levels of regulated on activation, normal T cell expressed and secreted (RANTES) and its receptor CCR5 in AT of obese mice. Adipocytes, stromal/vascular cells from mouse AT, and human and murine adipocytes expressed RANTES. RANTES mRNA levels were negatively correlated with adiponectin in mouse AT. Adiponectin-deficient mice fed high-fat diet showed higher RANTES mRNA levels in AT than wild-type mice. Activated T cells coincubated with preadipocytes in vitro significantly suppressed preadipocyte-to-adipocyte differentiation. Obese humans with metabolic syndrome had higher mRNA levels of RANTES and CCR5 in subcutaneous AT than lean humans. RANTES and CCR5 mRNA levels were significantly higher in visceral than subcutaneous AT of morbidly obese humans. RANTES mRNA levels were positively correlated with CD3 and CD11b in human visceral AT. Conclusions-Obesity is associated with increased accumulation of T cells and macrophages in AT, which may play important roles in obesity-related disease by influencing preadipocyte/adipocyte functions. RANTES is an adipokine that is upregulated in AT by obesity in both mice and humans.

Obesity is associated with chronic inflammation, which contributes to insulin resistance and type 2 diabetes mellitus. Under normal conditions, skeletal muscle is responsible for the majority of insulin-stimulated whole-body glucose disposal; thus, dysregulation of skeletal muscle metabolism can strongly influence whole-body glucose homeostasis and insulin sensitivity. Increasing evidence suggests that inflammation occurs in skeletal muscle in obesity and is mainly manifested by increased immune cell infiltration and proinflammatory activation in intermyocellular and perimuscular adipose tissue. By secreting proinflammatory molecules, immune cells may induce myocyte inflammation, adversely regulate myocyte metabolism, and contribute to insulin resistance via paracrine effects. Increased influx of fatty acids and inflammatory molecules from other tissues, particularly visceral adipose tissue, can also induce muscle inflammation and negatively regulate myocyte metabolism, leading to insulin resistance.

Obesity is becoming an epidemic in the United States and worldwide and increases risk for many diseases, particularly insulin resistance, type 2 diabetes mellitus, and cardiovascular disease. The mechanisms linking obesity with these diseases remain incompletely understood. Over the past 2 to 3 decades, it has been recognized that in obesity, inflammation, with increased accumulation and inflammatory polarization of immune cells, takes place in various tissues, including adipose tissue, skeletal muscle, liver, gut, pancreatic islet, and brain and may contribute to obesity-linked metabolic dysfunctions, leading to insulin resistance and type 2 diabetes mellitus. Therapies targeting inflammation have shed light on certain obesity-linked diseases, including type 2 diabetes mellitus and atherosclerotic cardiovascular disease, but remain to be tested further and confirmed in clinical trials. This review focuses on inflammation in adipose tissue and its potential role in insulin resistance associated with obesity.

Background-Monocyte activation and migration into the arterial wall are key events in atherogenesis associated with hypercholesterolemia. CD11c/CD18, a ␤ 2 integrin expressed on human monocytes and a subset of mouse monocytes, has been shown to play a distinct role in human monocyte adhesion on endothelial cells, but the regulation of CD11c in hypercholesterolemia and its role in atherogenesis are unknown. Methods and Results-Mice genetically deficient in CD11c were generated and crossbred with apolipoprotein E (apoE) Ϫ/Ϫ mice to generate CD11c Ϫ/Ϫ /apoE Ϫ/Ϫ mice. Using flow cytometry, we examined CD11c on blood leukocytes in apoE Ϫ/Ϫ hypercholesterolemic mice and found that compared with wild-type and apoE Ϫ/Ϫ mice on a normal diet, apoE Ϫ/Ϫ mice on a Western high-fat diet had increased CD11c ϩ monocytes. Circulating CD11c ϩ monocytes from apoE Ϫ/Ϫ mice fed a high-fat diet exhibited cytoplasmic lipid vacuoles and expressed higher levels of CD11b and CD29. Deficiency of CD11c decreased firm arrest of mouse monocytes on vascular cell adhesion molecule-1 and E-selectin in a shear flow assay, reduced monocyte/macrophage accumulation in atherosclerotic lesions, and decreased atherosclerosis development in apoE Ϫ/Ϫ mice on a high-fat diet. Conclusions-CD11c, which increases on blood monocytes during hypercholesterolemia, plays an important role in monocyte recruitment and atherosclerosis development in an apoE Ϫ/Ϫ mouse model of hypercholesterolemia. Key Words: atherosclerosis Ⅲ cell adhesion molecules Ⅲ leukocytes A therosclerosis associated with hypercholesterolemia is a complex inflammatory process, characterized pathologically by recruitment of monocytic leukocytes in the arterial wall and lipid accumulation in monocytic leukocytes. 1 Monocyte recruitment is a multistep process mediated by adhesion molecules, beginning with rolling, which is mediated by short-lived bonds between E-selectin on endothelial cells (ECs) and sialylated ligands such as P-selectin glycoprotein ligand-1 on monocytes, followed by firm arrest facilitated through interactions between activated ␤ 1 and ␤ 2 integrins on monocytes with vascular cell adhesion molecule-1 (VCAM-1) and intercellular adhesion molecule-1 (ICAM-1) on ECs. Firmly arrested monocytes subsequently undergo transmigration through other adhesion molecules. 2,3 Therefore, adhesion molecules participating in monocyte-EC interactions play a critical role in atherogenesis. 4 EC activation induced by hypercholesterolemia increases expression of VCAM-1, ICAM-1, and E-selectin, thereby contributing to atherogenesis. 4 -6 However, the effect of hypercholesterolemia on monocyte activation and its contribution to atherogenesis are less defined. Clinical Perspective on p 2717The ␤ 2 integrins, which include CD11a/CD18, CD11b/ CD18, CD11c/CD18, and CD11d/CD18, 7 contribute to atherogenesis as evidenced by a significant reduction in atherosclerosis development in CD18 Ϫ/Ϫ mice, which lack all 4 CD11/CD18 integrins. 4 CD11b has been used as an activation marker for monocytes/macrophages...

Background/ObjectivesLimited numbers of studies demonstrated obesity-induced macrophage infiltration in skeletal muscle (SM), but dynamics of immune cell accumulation and contribution of T cells to SM insulin resistance are understudied.Subjects/MethodsT cells and macrophage markers were examined in SM of obese humans by RT-PCR. Mice were fed high-fat diet (HFD) for 2–24 weeks, and time course of macrophage and T cell accumulation was assessed by flow cytometry and quantitative RT-PCR. Extramyocellular adipose tissue (EMAT) was quantified by high-resolution micro-CT, and correlation to T cell number in SM was examined. CD11a−/− mice and C57BL/6 mice were treated with CD11a-neutralizing antibody to determine the role of CD11a in T cell accumulation in SM. To investigate the involvement JAK/STAT, the major pathway for T helper I (TH1) cytokine IFNγ? in SM and adipose tissue inflammation and insulin resistance, mice were treated with a JAK1/JAK2 inhibitor, baricitinib.ResultsMacrophage and T cells markers were upregulated in SM of obese compared with lean humans. SM of obese mice had higher expression of inflammatory cytokines, with macrophages increasing by 2 weeks on HFD and T cells increasing by 8 weeks. The immune cells were localized in EMAT. Micro-CT revealed that EMAT expansion in obese mice correlated with T cell infiltration and insulin resistance. Deficiency or neutralization of CD11a reduced T cell accumulation in SM of obese mice. T cells polarized into a proinflammatory TH1 phenotype, with increased STAT1 phosphorylation in SM of obese mice. In vivo inhibition of JAK/STAT pathway with baricitinib reduced T cell numbers and activation markers in SM and adipose tissue and improved insulin resistance in obese mice.ConclusionsObesity-induced expansion of EMAT in SM was associated with accumulation and proinflammatory polarization of T cells, which may regulate SM metabolic functions through paracrine mechanisms. Obesity-associated SM “adiposopathy” may thus play an important role in development of insulin resistance and inflammation.

Objective Atherosclerosis is associated with monocyte adhesion to the arterial wall that involves integrin activation and emigration across inflamed endothelium. Involvement of β2-integrin CD11c/CD18 in atherogenesis was recently shown in dyslipidemic mice, which motivates our study of its inflammatory function during hypertriglyceridemia in humans. Methods and Results Flow cytometry of blood from healthy subjects fed a standardized high fat meal revealed that at 3.5 hours postprandial, monocyte CD11c surface expression was elevated and the extent of upregulation correlated with blood triglycerides. Monocytes from postprandial blood exhibited an increased light scatter profile, which correlated with elevated CD11c expression and uptake of lipid particles. Purified monocytes internalized triglyceride-rich lipoproteins isolated from postprandial blood through LRP-1, and this also elicited CD11c upregulation. Lab-on-a-chip analysis of whole blood showed that monocyte arrest on a VCAM-1 substrate under shear flow was elevated at 3.5 hours and correlated with blood triglyceride and CD11c expression. At 7 hours postprandial, blood triglycerides decreased and monocyte CD11c expression and arrest on VCAM-1 returned to fasting levels. Conclusions During hypertriglyceridemia, monocytes internalize lipid, upregulate CD11c, and increase adhesion to VCAM-1. These data suggest that analysis of monocyte inflammation may provide additional framework for evaluating individual susceptibility to cardiovascular disease.

Objective To examine infiltration of blood foamy monocytes, containing intracellular lipid droplets, into early atherosclerotic lesions and its contribution to development of nascent atherosclerosis. Approach and Results In apoE−/− mice fed western high-fat diet (WD), >10% of circulating monocytes became foamy monocytes at 3 days on WD and >20% of monocytes at 1 week. Foamy monocytes also formed early in blood of Ldlr−/−Apobec1−/− (LDb) mice on WD. Based on CD11c and CD36, mouse monocytes were categorized as CD11c−CD36−, CD11c−CD36+ and CD11c+CD36+. The majority of foamy monocytes were CD11c+CD36+, whereas most nonfoamy monocytes were CD11c−CD36− or CD11c−CD36+ in apoE−/− mice on WD. In wild-type mice, CD11c+CD36+ and CD11c−CD36+, but few CD11c−CD36−, monocytes took up cholesteryl ester–rich very-low-density lipoproteins (CE-VLDLs) isolated from apoE−/− mice on WD, and CE-VLDL uptake accelerated CD11c−CD36+–to–CD11c+CD36+ monocyte differentiation. Ablation of CD36 decreased monocyte uptake of CE-VLDLs. Intravenous injection of DiI-CE-VLDLs in apoE−/− mice on WD specifically labeled CD11c+CD36+ foamy monocytes, which infiltrated into nascent atherosclerotic lesions and became CD11c+ cells that were selectively localized in atherosclerotic lesions. CD11c deficiency reduced foamy monocyte infiltration into atherosclerotic lesions. Specific and consistent depletion of foamy monocytes (for 3 weeks) by daily intravenous injections of low-dose clodrosome reduced development of nascent atherosclerosis. Conclusions Foamy monocytes, which form early in blood of mice with hypercholesterolemia, infiltrate into early atherosclerotic lesions in a CD11c-dependent manner and play crucial roles in nascent atherosclerosis development.

Objective-To examine CD11c, a ␤ 2 -integrin, on adipose tissue (AT) leukocytes and blood monocytes and its role in diet-induced obesity. Methods and Results-High-fat diet-induced obese C57BL/6 mice, CD11c-deficient mice, and obese humans were studied. CD11c, leukocytes, and chemokines/cytokines were examined in AT and/or blood by flow cytometry, RNase protection assay, quantitative polymerase chain reaction, or enzyme-linked immunosorbent assay. Obese C57BL/6 mice had increased CD11c in AT and blood compared with lean controls. CD11c messenger RNA positively correlated with monocyte chemoattractant protein 1 in human visceral AT. Obese humans with metabolic syndrome had a higher CD11c level on blood monocytes compared with lean humans. Low-fat diet-induced weight loss reduced blood monocyte CD11c in obese mice and humans. Mouse and human monocyte CD11c levels and mouse AT CD11c messenger RNA correlated with insulin resistance. CD11c deficiency in mice did not alter weight gain but decreased inflammation, evidenced by a lower T-cell number and reduced levels of major histocompatibility complex class II, C-C chemokine ligand 2 (CCL5), CCL4, and interferon ␥ in AT, and ameliorated insulin resistance and glucose intolerance associated with diet-induced obesity. Conclusions-Diet-induced obesity increased CD11c in both AT and blood in mice and humans. CD11c plays an important role in T-cell accumulation and activation in AT, and contributes to insulin resistance associated with obesity. Key Words: inflammation Ⅲ obesity O besity increases the risk for type 2 diabetes and cardiovascular disease. Chronic inflammation, which occurs in obesity, has been acknowledged as an important link between obesity and the development of diabetes and cardiovascular disease. Adipose tissue (AT) synthesizes and secretes proinflammatory substances, such as cytokines, which are upregulated in obesity and may play important roles in mediating obesity-linked insulin resistance. 1 Chemokines, which contribute to inflammation because of their active properties for leukocyte trafficking and activation, have also been shown to be expressed by AT and increased in obesity. 2,3 Along with the increased levels of chemokines, such as monocyte chemoattractant protein (MCP) 1, or CCL2, and regulated on activation, normal T-cell expressed and secreted (RANTES), or CCL5, leukocytes, including macrophages and T cells, are increased in AT in obesity, and increased leukocytes in AT may contribute to obesity-linked metabolic abnormalities. 2,4 -7 Initial studies used CD11b and/or F4/80 to define total macrophages in AT. 4,5 Using mice fed a high-fat diet (HFD) for 3 weeks, we first reported a significant increase in CD11cϩ cells in AT. 8 Subsequently, other investigators reported an accumulation of F4/80 ϩ CD11c ϩ leukocytes in the AT of obese mice. 9,10 CD11c ϩ leukocytes in the AT of obese mice show proinflammatory characteristics of classically activated macrophages (M1) 9,10 and were demonstrated to play an important role in obesity-linked AT inflam...