Chronic Tumor Necrosis Factor Research Articles

Chronic TNF in the aging microenvironment exacerbates Tet2 loss-of-function myeloid expansion

AbstractSomatic mutations in the TET2 gene occur more frequently with age, imparting an intrinsic hematopoietic stem cells (HSCs) advantage and contributing to a phenomenon termed clonal hematopoiesis of indeterminate potential (CHIP). Individuals with TET2-mutant CHIP have a higher risk of developing myeloid neoplasms and other aging-related conditions. Despite its role in unhealthy aging, the extrinsic mechanisms driving TET2-mutant CHIP clonal expansion remain unclear. We previously showed an environment containing tumor necrosis factor (TNF) favors TET2-mutant HSC expansion in vitro. We therefore postulated that age-related increases in TNF also provide an advantage to HSCs with TET2 mutations in vivo. To test this hypothesis, we generated mixed bone marrow chimeric mice of old wild-type (WT) and TNF–/– genotypes reconstituted with WT CD45.1+ and Tet2–/– CD45.2+ HSCs. We show that age-associated increases in TNF dramatically increased the expansion of Tet2–/– cells in old WT recipient mice, with strong skewing toward the myeloid lineage. This aberrant myelomonocytic advantage was mitigated in old TNF–/– recipient mice, suggesting that TNF signaling is essential for the expansion Tet2-mutant myeloid clones. Examination of human patients with rheumatoid arthritis with clonal hematopoiesis revealed that hematopoietic cells carrying certain mutations, including in TET2, may be sensitive to reduced TNF bioactivity following blockade with adalimumab. This suggests that targeting TNF may reduce the burden of some forms of CHIP. To our knowledge, this is the first evidence to demonstrate that TNF has a causal role in driving TET2-mutant CHIP in vivo. These findings highlight TNF as a candidate therapeutic target to control TET2-mutant CHIP.

Chronic TNF exposure induces glucocorticoid-like immunosuppression in the alveolar macrophages of aged mice that enhances their susceptibility to pneumonia.

Chronic low-grade inflammation, particularly elevated tumor necrosis factor (TNF) levels, occurs due to advanced age and is associated with greater susceptibility to infection. One reason for this is age-dependent macrophage dysfunction (ADMD). Herein, we use the adoptive transfer of alveolar macrophages (AM) from aged mice into the airway of young mice to show that inherent age-related defects in AM were sufficient to increase the susceptibility to Streptococcus pneumoniae, a Gram-positive bacterium and the leading cause of community-acquired pneumonia. MAPK phosphorylation arrays using AM lysates from young and aged wild-type (WT) and TNF knockout (KO) mice revealed multilevel TNF-mediated suppression of kinase activity in aged mice. RNAseq analyses of AM validated the suppression of MAPK signaling as a consequence of TNF during aging. Two regulatory phosphatases that suppress MAPK signaling, Dusp1 and Ptprs, were confirmed to be upregulated with age and as a result of TNF exposure both exvivo and invitro. Dusp1 is known to be responsible for glucocorticoid-mediated immune suppression, and dexamethasone treatment increased Dusp1 and Ptprs expression in cells and recapitulated the ADMD phenotype. In young mice, treatment with dexamethasone increased the levels of Dusp1 and Ptprs and their susceptibility to infection. TNF-neutralizing antibody reduced Dusp1 and Ptprs levels in AM from aged mice and reduced pneumonia severity following bacterial challenge. We conclude that chronic exposure to TNF increases the expression of the glucocorticoid-associated MAPK signaling suppressors, Dusp1 and Ptprs, which inhibits AM activation and increases susceptibility to bacterial pneumonia in older adults.

Immune Differentiation Regulator p100 Tunes NF-κB Responses to TNF.

Tumor necrosis factor (TNF) is a pleiotropic cytokine whose primary physiological function involves coordinating inflammatory and adaptive immune responses. However, uncontrolled TNF signaling causes aberrant inflammation and has been implicated in several human ailments. Therefore, an understanding of the molecular mechanisms underlying dynamical and gene controls of TNF signaling bear significance for human health. As such, TNF engages the canonical nuclear factor kappa B (NF-κB) pathway to activate RelA:p50 heterodimers, which induce expression of specific immune response genes. Brief and chronic TNF stimulation produces transient and long-lasting NF-κB activities, respectively. Negative feedback regulators of the canonical pathway, including IκBα, are thought to ensure transient RelA:p50 responses to short-lived TNF signals. The non-canonical NF-κB pathway mediates RelB activity during immune differentiation involving p100. We uncovered an unexpected role of p100 in TNF signaling. Brief TNF stimulation of p100-deficient cells triggered an additional late NF-κB activity consisting of RelB:p50 heterodimers, which modified the TNF-induced gene-expression program. In p100-deficient cells subjected to brief TNF stimulation, RelB:p50 not only sustained the expression of a subset of RelA-target immune response genes but also activated additional genes that were not normally induced by TNF in WT mouse embryonic fibroblasts (MEFs) and were related to immune differentiation and metabolic processes. Despite this RelB-mediated distinct gene control, however, RelA and RelB bound to mostly overlapping chromatin sites in p100-deficient cells. Repeated TNF pulses strengthened this RelB:p50 activity, which was supported by NF-κB-driven RelB synthesis. Finally, brief TNF stimulation elicited late-acting expressions of NF-κB target pro-survival genes in p100-deficient myeloma cells. In sum, our study suggests that the immune-differentiation regulator p100 enforces specificity of TNF signaling and that varied p100 levels may provide for modifying TNF responses in diverse physiological and pathological settings.

Microbiota Induces Expression of Tumor Necrosis Factor in Postnatal Mouse Skin.

Tumor necrosis factor (TNF) is a pleiotropic cytokine that regulates many important processes in the body. TNF production in a physiological state supports the structure of lymphoid organs and determines the development of lymphoid cells in hematopoiesis. However, chronic TNF overexpression leads to the development of various autoimmune disorders. Sites of TNF production in the naïve state remain unclear due to the lack of in vivo models. In the present study, we used TNF-2A-Kat reporter mice to monitor the expression of TNF in different tissues. Comparative analysis of tissue fluorescence in TNF-2A-Kat reporter mice and wild type mice revealed constitutive expression of TNF in the skin of naïve adult mice. In the skin of TNF-2A-Kat reporter mouse embryos, no statistically significant differences in the expression of TNF compared to wild type animals were observed. Furthermore, we established that local depletion of microflora with topical antibiotics leads to a reduction in the fluorescence signal. Thus, we assume that the skin microflora is responsible for the expression of TNF in the skin of mice.

Exacerbation of tumor necrosis factor-induced vascular leak syndrome by aging.

Aging is associated with upregulation of tumor necrosis factor (TNF) and increased vascular inflammation. TNF is a major proinflammatory cytokine that contributes to both vascular inflammation and vascular leak syndrome (VLS). The purpose of this study was to investigate whether the aging affects TNF-induced VLS. Vascular leak, histology, and cytokine assays were performed in young and aged groups of wild-type and TNF overexpressing transgenic (Tg) mice. An aged group of TNF Tg mice showed substantially amplified VLS compared with young Tg mice. Age-related amplification of TNF-induced VLS appears to be related to local vascular fibrosis and the systemic upregulation of TNF and MCP-1 levels in older TNF Tg mice. Our finding suggests that chronic high-grade TNF exposure could mediate the severe vascular pathogenicity of VLS.

Perispinal etanercept for post-stroke neurological and cognitive dysfunction: scientific rationale and current evidence.

There is increasing recognition of the involvement of the immune signaling molecule, tumor necrosis factor (TNF), in the pathophysiology of stroke and chronic brain dysfunction. TNF plays an important role both in modulating synaptic function and in the pathogenesis of neuropathic pain. Etanercept is a recombinant therapeutic that neutralizes pathologic levels of TNF. Brain imaging has demonstrated chronic intracerebral microglial activation and neuroinflammation following stroke and other forms of acute brain injury. Activated microglia release TNF, which mediates neurotoxicity in the stroke penumbra. Recent observational studies have reported rapid and sustained improvement in chronic post-stroke neurological and cognitive dysfunction following perispinal administration of etanercept. The biological plausibility of these results is supported by independent evidence demonstrating reduction in cognitive dysfunction, neuropathic pain, and microglial activation following the use of etanercept, as well as multiple studies reporting improvement in stroke outcome and cognitive impairment following therapeutic strategies designed to inhibit TNF. The causal association between etanercept treatment and reduction in post-stroke disability satisfy all of the Bradford Hill Criteria: strength of the association; consistency; specificity; temporality; biological gradient; biological plausibility; coherence; experimental evidence; and analogy. Recognition that chronic microglial activation and pathologic TNF concentration are targets that may be therapeutically addressed for years following stroke and other forms of acute brain injury provides an exciting new direction for research and treatment.

Inhibition of TNF in the Brain Reverses Alterations in RAS Components and Attenuates Angiotensin II-Induced Hypertension

Dysfunction of brain renin-angiotensin system (RAS) components is implicated in the development of hypertension. We previously showed that angiotensin (Ang) II-induced hypertension is mediated by increased production of proinflammatory cytokines (PIC), including tumor necrosis factor (TNF), in brain cardiovascular regulatory centers such as the paraventricular nucleus (PVN). Presently, we tested the hypothesis that central TNF blockade prevents dysregulation of brain RAS components and attenuates Ang II-induced hypertension. Male Sprague-Dawley rats were implanted with radio-telemetry transmitters to measure mean arterial pressure (MAP) and subjected to intracerebroventricular (ICV) infusion of etanercept (10 µg/kg/day) with/without concurrent subcutaneous 4-week Ang II (200 ng/kg/min) infusion. Chronic Ang II infusion resulted in a significant increase in MAP and cardiac hypertrophy, which was attenuated by inhibition of brain TNF with etanercept. Etanercept treatment also attenuated Ang II-induced increases in PIC and decreases in IL-10 expression in the PVN. Additionally, Ang II infusion increased expression of pro-hypertensive RAS components (ACE and AT1R), while decreasing anti-hypertensive RAS components (ACE2, Mas, and AT2 receptors), within the PVN. ICV etanercept treatment reversed these changes. Ang II-infusion was associated with increased oxidative stress as indicated by increased NAD(P)H oxidase activity and super oxide production in the PVN, which was prevented by inhibition of TNF. Moreover, brain targeted TNF blockade significantly reduced Ang II-induced NOX-2 and NOX-4 mRNA and protein expression in the PVN. These findings suggest that chronic TNF blockade in the brain protects rats against Ang II-dependent hypertension and cardiac hypertrophy by restoring the balance between pro- and anti-hypertensive RAS axes and inhibiting PIC and oxidative stress genes and proteins in the PVN.

TNF is required for the induction but not the maintenance of compression‐induced BME signals in murine tail vertebrae: Limitations of anti‐TNF therapy for degenerative disc disease

While bone marrow edema (BME) is diagnostic of spondyloarthropathy, its nature remains poorly understood. In contrast, BME in ankylosing spondylitis is caused by tumor necrosis factor (TNF)-induced vascular and cellular changes. To investigate the relationship between chronic compression and TNF signaling in compression-induced BME we utilized a tail vertebrae compression model with WT, TNF-Tg, and TNFR1&2-/- mice to evaluate: (i) healing following release of chronic compression, (ii) induction of BME in the absence of TNFR, and (iii) efficacy of anti-TNF therapy. Compression-induced normalized marrow contrast enhancement (NMCE) in WT was significantly decreased threefold (p < 0.01) within 2 weeks of release, while the NMCE values in TNF-Tg vertebrae remained elevated, but had a significant decrease (p < 0.05) by 6 weeks after the release of compression. TNFR1&2-/- mice were resistant to compression-induced BME. Anti-TNF therapy did not affect NMCE versus placebo. Histological examination revealed that NMCE values significantly correlated with marrow vascularity and cellularity (p < 0.05), which account for 76% of the variability of NMCE. Collectively, these data demonstrate a critical role for TNF in the induction of chronic compression-induced BME, but not in its maintenance. Amelioration of BME is achieved through biomechanical stability, but is not affected by anti-TNF therapy.

TNF activates an IRF1-dependent autocrine loop leading to sustained expression of chemokines and STAT1-dependent type I interferon–response genes

Rapid induction of inflammatory genes by tumor necrosis factor (TNF) has been well studied, but little is known about delayed and chronic TNF responses. Here we investigated the kinetics of primary macrophage responses to TNF and discovered that TNF initiates an interferon-beta-mediated autocrine loop that sustains expression of inflammatory genes and induces delayed expression of interferon-response genes such as those encoding the transcription factors STAT1 and IRF7, which enhance macrophage responses to stimulation of cytokines and Toll-like receptors. TNF-induced interferon-beta production depended on interferon-response factor 1, and downstream gene expression was mediated by synergy between small amounts of interferon-beta and canonical TNF-induced signals. Thus, TNF activates a 'feed-forward' loop that sustains inflammation but avoids the potential toxicity associated with the high interferon production induced by stimulation of Toll-like receptors.

Tumor necrosis factor-α up-regulates the expression of CCL2 and adhesion molecules of human proximal tubular epithelial cells through MAPK signaling pathways

Both circulating and urinary tumor necrosis factor (TNF)- α levels have been shown to increase in inflammatory chronic kidney diseases and TNF- α can induce secretion of other inflammatory mediators from many cell types. Chemokine, mononuclear chemoattractant protein-1 (CCL2/MCP-1), and cell surface adhesion molecules, intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1), in renal proximal tubular epithelial cells (PTEC) are important for promoting recruitment and adhesion of infiltrating macrophages and lymphocytes to inflamed renal tissue. This study aimed to investigate the effect of TNF- α on the expression of these inflammation-related molecules of human PTEC and the underlying intracellular mitogen-activated protein kinase (MAPK) regulatory signaling mechanisms. Cytokine expression profile of TNF- α-activated PTEC was assayed by protein array. The concentration of CCL2 was analyzed by ELISA, while the expression of cell surface ICAM-1 and VCAM-1 and intracellular phosphorylated p38 MAPK, c-Jun NH2-terminal kinase (JNK) and extracellular signal-regulated kinase (ERK) was assessed using flow cytometry. TNF- α could significantly induce CCL2, ICAM-1 and VCAM-1 expression of PTEC. Selective inhibitors of p38 MAPK (SB203580), JNK (SP600125) and ERK (PD98059) could suppress TNF- α-induced CCL2 and ICAM-1 expression, while only p38 MAPK and ERK inhibitors could suppress TNF- α-induced VCAM-1 expression. JNK inhibitor was found to up-regulate VCAM-1 expression but did not elicit any additive effect with TNF- α on VCAM-1 expression. Moreover, p38 MAPK inhibitor was found to abrogate the TNF- α-induced ERK phosphorylation, suggesting that there was a one-way interaction between p38 MAPK and ERK pathways during the TNF- α activation. TNF- α can play a crucial role in the immunopathogenesis of nephritis by the induction of CCL2, ICAM-1 and VCAM-1 expression via the activation of the intracellular MAPK signaling pathway, which may contribute to macrophage and lymphocyte infiltration.

Defining psoriasis subtypes: features of severe psoriasis and associated diseases

Evaluation of: Christensen TE, Callis CP, Papenfuss J et al. Observations of psoriasis in the absence of therapeutic intervention identifies two unappreciated morphologic variants, thin-plaque and thick-plaque psoriasis, and their associated phenotypes. J. Invest. Dermatol. 126, 2397–2403 (2006) .Psoriasis is a common immune-mediated inflammatory disease showing a variety of differing phenotypes. In the evaluated paper, attempts were made to classify plaque-psoriasis according to lesional thickness. It was noted that patients with thick plaques demonstrated obesity together with extensive body involvement. In addition, patients suffered from comorbidities including psoriatic arthritis. In contrast to thin or intermediate plaque thickness, patients with this phenotype suffer from lasting disease and a considerable inflammatory load, both of which could lead to the development of insulin resistance. As noted in studies of rheumatoid arthritis, chronic tumor necrosis factor α–regulated inflammation respresents a major cause for metabolic syndrome-related cardiovascular disease.

High adiponectin and TNF-α levels in moderate drinkers suffering from liver steatosis: comparison with non drinkers suffering from similar hepatopathy

Moderate alcohol consumption is associated with increased insulin sensitivity and a reduced risk for type 2 diabetes. An important endogenous mediator of insulin sensitivity is adiponectin (AN), an adipokine that displays numerous antiatherogenic, antidiabetogenic and antiinflammatory effects. Recently, acute increase in alcohol consumption has been shown to be associated with increase in plasma adiponectin and, concomitantly, insulin sensitivity. Whether chronic alcohol consumption predicts an increase in plasma AN and whether this is independent of adiposity, markers of liver dysfunction, and plasma adipokines such as tumor necrosis factor (TNF)-alpha is not known. We, therefore, investigated these relationships in 75 men who were diagnosed with liver steatosis using ultrasound/liver biopsy. We examined 75 men, who were diagnosed for having liver steatosis (ultrasound/liver biopsy). Each filled in a questionnaire on alcohol intake. Subjects were divided into two subgroups according to alcohol history and CDT concentrations--drinkers and non-drinkers. All individuals were examined for serum concentrations of AN, glucose, triglycerides, alanine aminotransferase (ALT), aspartate aminotransferase (AST) and glutamate transferase (GMT) activity; carbohydrate-deficient transferrin (CDT%) a marker of chronic alcohol consumption, insulin and TNF-alpha. The Quicki insulin sensitivity index was calculated. Forty-eight individuals were found to be moderate drinkers and 27 subjects non-drinkers. Moderate drinkers had significantly higher concentrations of AN (13.8 +/- 3,7 versus 9.1 +/- 5.4 mg/l, means +/- SD, p = 0.012) compared with non-drinkers, independent of adiposity. Plasma AN concentrations in the whole group were positively correlated with TNF-alpha concentrations (r = 0.6; p = 0.0001), CDT (r = 0.26; p = 0.0084), AST/ALT index (r = 0.3, p = 0.009), AST (r = 0.29; p = 0.011) and GMT (r = 0.29; p = 0.011) and negatively with BMI (r = -0.48; p = 0.0002) and glycemia (r = -0.22; p = 0.049). The positive associations of AN with TNF-alpha (0.8; p = 0.001), CDT (0.55; p = 0.017), AST/ALT index (0.55; p = 0.019) and the negative correlation with glycemia (-0.35; p = 0.0158) were independent of BMI. Stratified according to alcohol intake, in moderate drinkers, a positive correlation was found between AN and TNF-alpha concentrations (r = 0.6, p = 0.0001, AST/ALT index (r = 0.34, p = 0.0295) whereas in non-drinkers no such correlations were found. The concentration of AN and BMI displayed a negative correlation in both drinker and nondrinker patients (r = -0.42, p = 0.01 and -0.61; p = 0.012, respectively). We concluded that plasma AN is higher in moderate drinkers compared to non-drinkers, even after correction for BMI. Drinkers suffering from liver steatosis were found to have a positive correlation between AN concentrations, laboratory markers of liver disease and TNF-alpha. Such correlation was absent in non-drinkers suffering from liver steatosis. This suggests that alcohol may modulate the inhibitory effect of TNF-alpha on AN production, and thus, increase its plasma concentrations.

Granulomatous lung disease occurring during etanercept treatment

Introduction Tumor necrosis factor (TNF ) is an important mediator of the molecular cascade that leads to chronic inflammation. It induces chemokine production, which results in the recruitment of leukocytes into the local environment, and upregulates adhesion molecules on vascular endothelial cells, which also promotes the localization of leukocytes into the inflamed tissue. Animal models suggest that TNF also plays an important role in the formation and maintenance of granulomas (1). Granulomas form in response to either infection or an inflammatory stimulus, and are composed of organized aggregations of activated macrophages surrounded by lymphocytes and fibroblasts (2). Fibroblasts surrounding the granuloma produce a fibrous capsule, and this tissue reaction may help protect the host from an inciting agent by maintaining containment and reducing the nutrient availability to potential infectious agents. Sensitized CD4 T cells with a Th1 pattern of cytokine production help initiate and maintain the structure, and cross-talk between T lymphocytes and macrophages is also important for maintenance. Both interferon gamma and TNF inhibit microbial growth, and have a synergistic effect on macrophage activation. Blockade of TNF results in down regulation of many adhesion molecules, and decreases circulating inflammatory cytokines. Etanercept is an anti–TNF therapy developed for the treatment of inflammatory arthritis. It is a fusion protein that consists of the extracellular ligandbinding domain of the TNF receptor coupled to the Fc portion of human IgG. It is thought to work by binding TNF and blocking its interaction with TNF receptors, thereby rendering TNF inactive. Chronic TNF inhibition has been rarely associated with reactivation of selected infections such as mycobacterial infections, which require granuloma formation for host response. Previous studies have suggested that anti–TNF therapy may result in diminished granuloma formation (3). For this reason anti–TNF therapy is being evaluated in sarcoidosis, a disease characterized by the formation of granulomas (4). Although much is known about the mediators involved in cytokine production in granulomatous diseases, the exact role of TNF remains unclear, as the following case illustrates. We report a patient who developed a pulmonary granulomatosis reaction (culture negative) while receiving etanercept therapy for psoriatic arthritis.

Tumor necrosis factor induces sodium retention in diabetic rats through sequential effects on distal tubule cells

Tumor necrosis factor (TNF) contributes to sodium retention during diabetes. TNF selectively stimulates sodium uptake in distal tubule cells isolated from diabetic rats, but not in cells from control rats. We propose that distal tubule cells are sensitized to acute effects of TNF during diabetes. We examined acute TNF-stimulated sodium uptake in distal tubule cells chronically cultured with exogenous TNF and in distal tubule cells freshly isolated from diabetic rats treated with a specific TNF inhibitor. We also tested the sodium transport and intracellular signaling pathway underlying TNF-induced sodium transport with pharmacologic inhibitors. Chronic TNF exposure in vitro sensitized distal tubule cells to the acute effects of TNF in a time- and dose-dependent manner, and TNF inhibition in vivo during diabetes prevented distal tubule sensitization. TNF receptor expression was equivalent in distal tubule cells from both control and diabetic rats. In sensitized distal tubule cells, TNF-stimulated sodium uptake was blocked by amiloride and PD098059, inhibitors of epithelial sodium channels and extracellular signal-related protein kinase (ERK) activation, respectively. TNF alters distal tubule sodium transport during diabetes through consecutive chronic and acute effects. Chronic TNF exposure leads to distal tubule sensitization that permits acute TNF-induced activation of epithelial sodium channel (ENaC). These findings are consistent with a sequential mechanism by which chronic and acute TNF actions at the distal tubule cellular level contribute to whole animal sodium retention during diabetes.

TNF inhibition at the time of myocardial infarction attenuates the subsequent development of heart failure

Background: Tumor necrosis factor (TNF) causes myocardial contractile dysfunction, extracellular matrix (ECM) remodeling, and fibrosis in models of myocardial ischemia, infarction, and chronic heart failure (CHF). Results of chronic TNF inhibition in preclinical and clinical CHF trials suggest that TNF plays both a beneficial and a detrimental role in CHF. This study was undertaken to examine the effects of short-term inhibition of TNF in the early period following myocardial infarction, when expression is highest. We hypothesized that TNF inhibition in this time frame would prevent the subsequent development of heart failure.

Targeted disruption of ICAM-1, P-selectin genes improves cardiac function and survival in TNF-alpha transgenic mice.

We have developed a transgenic mouse model in which tumor necrosis factor (TNF)-alpha is overexpressed exclusively in the heart under the regulation of the alpha-myosin heavy chain promoter. These animals develop chronic heart failure associated with severe leukocyte infiltration in both the atria and the ventricles. The purpose of this study was to investigate the role of adhesion molecules in mediating cardiac dysfunction in the TNF-alpha transgenic model. TNF-alpha transgenic mice were bred with mice null for intercellular adhesion molecule (ICAM)-1 and P-selectin genes to obtain a lineage of ICAM-1 and P-selectin null mice with selective overexpression of TNF-alpha in the heart. TNF-alpha transgenic animals showed marked upregulation of ICAM-1 mRNA and protein; however, P-selectin mRNA and protein remained undetectable despite chronic TNF overexpression. Cardiac function was markedly improved in the ICAM-1(-/-), P-selectin(-/-), TNF-alpha transgenic group versus the ICAM(+/+), P-selectin(+/+), TNF-alpha transgenic group. Kaplan-Meier survival curves showed statistically significant prolonged survival in the ICAM-1(-/-), P-selectin(-/-), TNF-alpha transgenic animals. These data suggest that ICAM-1 mediates at least in part the cardiac dysfunction induced by TNF-alpha expression by cardiac myocytes.

Effects of acute or chronic administration of tumor necrosis factor on rat adipose tissue development.

Because tumor necrosis factor (TNF) inhibits adipose cell differentiation in vitro and affects lipid metabolism in vivo, we treated adult or newborn rats for 1 wk with daily intraperitoneal injections (100 U/g of body weight) or continuous intraperitoneal diffusion (3500 U/h) of human recombinant TNF. Three weeks after the end of treatment, the long-term effect of the cytokine was examined on adipose tissue development. Control and TNF-injected rats did not differ in growth or development of perirenal, retroperitoneal and epididymal adipose tissues. Nevertheless, the size distribution of epididymal adipocytes of adult injected rats presented a slight shift towards larger values in the cytokine group. When TNF was administered chronically, the cytokine exerted an anorectic effect, which was alleviated after the end of treatment. The weights of the excised adipose tissues were depressed (P < .025) by TNF administration. Part of this effect was due to the induced anorexia. The size distributions of the epididymal adipocytes of pair-fed and TNF-treated rats were both shifted to smaller (P < 0.01) values than for the controls. The ratio of triglycerides over total lipids was, however, reduced by TNF specifically, but only at the retroperitoneal (P < .05) and not the epididymal site. These results indicate that in contrast to acute treatment, chronic TNF treatment slightly inhibited adipose tissue development in vivo; however, most of this effect was attributable to the associated anorexia.