Prostaglandins E2 and F2 alpha are not involved in the monocytic-product (interleukin-1)-induced stimulation of hepatic fibrinogen synthesis in rats

1. Monocytic products, especially interleukin-1 (IL-1), play an important role in the acute-phase response. Prostaglandins have been shown to act as second messengers in several physiological alterations of the acute-phase response, such as fever, muscle wasting and immunoregulation. The present study was undertaken to determine the role of prostaglandins in the monocytic-product-induced stimulation of the hepatic synthesis of fibrinogen, a well-known acute-phase protein. 2. Prostaglandin (PG) E2, PGF2 alpha and 16,16-dimethyl-PGE2 did not stimulate fibrinogen synthesis and fibrinogen polypeptide mRNA content when administered intraperitoneally to rats or when added to monolayer cultures of rat hepatocytes. 3. Cyclo-oxygenase inhibitors did not abolish the stimulation of fibrinogen synthesis and its mRNA content induced by monocytic products in vivo or in vitro. 4. These findings indicate that the enhanced synthesis of fibrinogen induced by monocytic products (including IL-1) during the acute-phase response is not mediated by prostaglandins or other products of the cyclo-oxygenase pathway of arachidonic acid.     

Role of acute-phase proteins in interleukin-1-induced nonspecific resistance to bacterial infections in mice.

Treatment with a single low dose (80 to 800 ng) of interleukin-1 (IL-1) 24 h before a lethal bacterial challenge of granulocytopenic and normal mice enhances nonspecific resistance. Since IL-1 induces secretion of acute-phase proteins, liver proteins which possess several detoxifying effects, we investigated the role of these proteins in the IL-1-induced protection. Inhibition of liver protein synthesis with D-galactosamine (GALN) completely inhibited the IL-1-induced synthesis of acute-phase proteins. GALN pretreatment abolished the protective effect of IL-1 on survival completely (neutropenic mice infected with Pseudomonas aeruginosa) or partially (nonneutropenic mice infected with Klebsiella pneumoniae). Pretreatment with IL-6, a cytokine induced by IL-1, did not reproduce the protection offered after IL-1 pretreatment, nor did it enhance or deteriorate the IL-1-enhanced resistance to infection. A protective effect of IL-1 via effects on glucose homeostasis during the acute-phase response was investigated by comparing plasma glucose levels in IL-1-treated mice and control mice before and during infection. Although glucose levels in IL-1-pretreated mice were somewhat higher in the later stages of infection, no significant differences from levels in control mice were present, and the glucose levels in control-treated animals never fell to hypoglycemic values. We conclude that the IL-1-induced nonspecific resistance is mediated neither by the induction of IL-6 nor by the effects of IL-1 on glucose homeostasis. Acute-phase proteins generated after IL-1 pretreatment, however, seem to play a critical role in the IL-1-induced protection to infection.     

Prostaglandin-E2 is a potent inhibitor of human interleukin 12 production

During human immunodeficiency virus infection and allergic diseases, characterized by a dominant T helper (Th) 2 response, overproduction of prostaglandin E2 (PGE2) is observed. In this paper we studied the effect of PGE2 on interleukin (IL)-12 synthesis, because this cytokine has been described to be essential in induction of Th1 responses. IL-12 synthesis was induced in monocytes that were stimulated with Neisseria meningitidis-derived lipopolysaccharide in whole blood cultures. PGE2 almost completely inhibited lipopolysaccharide induced IL-12 production, whereas IL-6 production was only partially inhibited by PGE2. In contrast, the production of IL-10 was approximately twofold enhanced at these conditions. The effects of PGE2 were due to its cAMP- inducing capacity, since they could be mimicked by other cAMP inducers. Recombinant human IL-10 also inhibited IL-12 and IL-6 production. However, the inhibitory effect of PGE2 on IL-12 production was independent of IL-10 since neutralizing anti-IL-10 antibodies were unable to reverse this inhibition. These results suggest that the capacity of an antigen to induce PGE2 synthesis may play a crucial role in the development of either a Th1 or Th2 response.     

Platelet-derived interleukin 1 induces human endothelial adhesion molecule expression and cytokine production

Interleukin 1 (IL-1) plays a central role in the regulation of the body's response to infectious and inflammatory stimuli. Recent evidence has shown that human platelets express a cell associated form of this proinflammatory cytokine very rapidly following activation. Since one of the earliest events in inflammation is frequently the rapid adhesion of platelets to injured endothelium, it was of interest to determine whether platelets express IL-1 in a functionally relevant form that can alter the phenotype of human endothelial cells in vitro. Thrombin activated platelets induced significant expression of the adhesion molecule intercellular adhesion molecule 1, as well as secretion of the IL-1 inducible cytokines IL-6 and granulocyte macrophage colony stimulating factor by cultured human umbilical cord and saphenous vein endothelial cells. This was inhibited by prior treatment of the platelets with antibody specific for IL-1. These results suggest that platelet delivered IL-1 might initiate and regulate some of the earliest phases of the inflammatory response. An additional observation of interest was differential induction of endothelial leucocyte adhesion molecule 1 by activated platelets on saphenous vein but not umbilical vein but not umbilical vein endothelial cells, which suggests functional heterogeneity of the endothelial cells.     

Kupffer cell-depleted rats have a diminished acute-phase response following major liver resection

Partial hepatectomy (PH)-induced Kupffer cell (KC) activation results in a rapid release of cytokines inducing the acute-phase response (APR). This study was done to evaluate the role of Kupffer cells (KCs) in the course of the APR following PH and a consecutive endotoxin challenge. KC depletion was performed in rats by i.v. administration of 1 mL liposome-encapsulated dichloromethylene diphosohonate (Cl2MDP). Control rats received 1 mL NaCl 0.9%. Forty-eight hours later, PH was performed. At 24 h after PH, rats were randomized to receive either 1 mL NaCl 0.9% (saline) or 50 microg/kg LPS i.v. in 1 mL. Animals were sacrificed at 4 h after LPS or saline infusion. The APR was determined by measuring hepatic gene expression of alpha 2-macroglobulin, alpha 1-acid glycoprotein, and IL-6 and expression of hepatic albumin. The APR was significantly depressed in KC-depleted rats. Despite increased IL-6 mRNA synthesis in response to low-dose LPS, no enhancement of acute-phase protein synthesis (APP) was found in KC-depleted rats. Hepatic failure was most profound in KC-depleted rats, as indicated by elevated plasma levels of liver transaminases and ammonia. We conclude that after PH, KC function in the remnant liver is important for the acute-phase reaction and reduces endotoxin-induced hepatocyte damage.     

Role of interleukin 6 (IL-6) in protection from lethal irradiation and in endocrine responses to IL-1 and tumor necrosis factor

Primary responsibility for the induction of various acute phase reactions has been ascribed to interleukin 1 (IL-1), tumor necrosis factor (TNF), or IL-6, suggesting that these cytokines may have many overlapping activities. Thus, it is difficult to identify the cytokine primarily responsible for a particular biologic effect, since IL-1 and TNF stimulate one another, and both IL-1 and TNF stimulate IL-6. In this work, the contribution of IL-6 in radioprotection, induction of adrenocorticotropic hormone (ACTH), and induction of hypoglycemia was assessed by blocking IL-6 activity. Administration of anti-IL-6 antibody to otherwise untreated mice greatly enhanced the incidence of radiation-induced mortality, indicating that like IL-1 and TNF, IL-6 also contributes to innate resistance to radiation. Anti-IL-6 antibody given to IL-1-treated or TNF-treated mice reduced survival from lethal irradiation, demonstrating that IL-6 is also an important mediator of both IL-1- and TNF-induced hemopoietic recovery. A similar IL-1/IL-6 interaction was observed in the case of ACTH induction. Anti-IL-6 antibody blocked the IL-1-induced increase in plasma ACTH, whereas recombinant IL-6 by itself did not induce such an increase. Anti-IL-6 antibody also mitigated TNF-induced hypoglycemia, but did not reverse IL-1-induced hypoglycemia. It is, therefore, likely that TNF and IL-1 differ in their mode of induction of hypoglycemia. Our results suggest that an interaction of IL-6 with IL-1 and TNF is a prerequisite for protection from radiation lethality, and its interaction with IL-1 for induction of ACTH.     

Induction of hapten-specific tolerance by interleukin 10 in vivo

Interleukin 10 (IL-10) is released during the induction phase of contact sensitivity and was shown in prior functional studies to convert epidermal Langerhans cells (LC) from potent inducers of primary immune responses to specifically tolerizing cells in vitro. To investigate whether IL-10 also subserves the function of a tolerizing agent in vivo ears of BALB/c or C3H mice were injected intradermally with 1-2 micrograms of recombinant mouse (rm)IL-10 8 h before epicutaneous application of 3% trinitrochlorobenzene (TNCB; a contact allergen). As a control, mice were injected with phosphate-buffered saline or IL-10 plus neutralizing amounts of anti-IL-10 mAb. 5 d later, mice were challenged with 1% TNCB on contralateral ears and ear swelling response was measured 24 h later. Whereas control-treated mice showed a normal ear swelling response to epicutaneous challenge (delta mm-2 = 25 +/- 5), ear swelling response of IL-10-treated animals was significantly inhibited (delta mm-2 = 3 +/- 2). Coinjection of IL-10- specific mAb together with rmIL-10 completely abrogated this effect. To differentiate between a state of nonresponsiveness and induction of tolerance by IL-10, mice initially treated with IL-10 and TNCB were resensitized with 3% TNCB in the absence of any treatment after 14 d of rest (group 1). Again mice were challenged 5 d later and ear swelling responses were tested. Whereas control mice treated with allergen alone (group 2) showed a good swelling response (delta mm-2 = 28 +/- 6), IL- 10-treated mice (group 1) showed a minimal response towards application of allergen (delta mm-2 = 4 +/- 2). To show that anergy induction by IL- 10 was antigen-specific, mice initially treated with IL-10 plus TNCB were exposed to 0.5% dinitrofluorobenzene (DNFB) 14 d later (group 1). After challenge with 0.1% DNFB, IL-10-treated mice showed an ear swelling response (delta mm-2 = 13 +/- 3; group 1) similar to that of control mice only sensitized with DNFB (delta mm-2 = 14 +/- 3; group 3). In an attempt to show the induction of antigen-specific tolerance in these mice in vitro, regional lymph nodes of mice initially treated with TNCB plus IL-10 (group 1) and control-treated mice (groups 2 and 3) were prepared and cultured in the presence of TNBS, dinitrobenzene sulfonate (DNBS), or medium to measure antigen-specific proliferation.(ABSTRACT TRUNCATED AT 400 WORDS)     

Spinal interleukin-1beta reduces inflammatory pain

Inflammation or injury often lead to chronic pain states such as hyperalgesia where the perception of a normally painful stimulus is significantly exaggerated. Interleukin-1beta (IL-1beta) is a cytokine that is an important mediator of the inflammatory response. In addition, IL-1beta has been implicated in the modulation of pain transmission in both the peripheral and central nervous systems. We evaluated the spinal effect of this cytokine in the presence and absence of a peripheral carrageenan inflammation in rats since the spinal cord is a major region of the central nervous system in which nociceptive input is processed and modulated. Our results indicate that intrathecal IL-1beta has no effect on the latency of paw withdrawal in response to a noxious thermal stimuluation in normal rats. In contrast, we have observed that IL-1beta produces significant antinociception when administered intrathecally in rats with peripheral inflammation (carrageenan model). The IL-1beta effect appears to be selective as it is reversed when IL-1beta is administered in the presence of an IL-1beta neutralizing antibody. We evaluated some putative mechanisms of this IL-1beta-mediated antinociception and found it to be non-opioid-dependent. Collectively, these data indicate that intrathecal IL-1beta has no effect on the processing of thermal nociceptive information in the absence of a peripheral inflammation. Therefore, the response to acute pain remains normal in these rats. In contrast, IL-1beta is antinociceptive when applied spinally during inflammation. These results indicate that IL-1beta reduces inflammatory hyperalgesia while sparing the protective functions of acute pain. This study offers new insights into the role of IL-1beta and nociceptive processing at the level of the spinal cord and suggests that development of IL-1beta agonists may be an alternative to opiate based therapies in the treatment of inflammatory pain.     

Induction of interleukin 1 alpha mRNA during the antigen-dependent interaction of sensitized T lymphoblasts with macrophages

DNA-RNA hybridization with an IL-1 alpha cDNA probe was used to monitor the induction of IL-1 in macrophages that were acting as accessory cells for the proliferation of T lymphocytes. Mouse peritoneal macrophages bound and stimulated T lymphocytes in the presence of the mitogens, Con A, or anti-CD3 mAb, but little or no IL-1 mRNA was detectable. In contrast, if the T cells were first sensitized in a mixed leukocyte reaction with dendritic cells and then added to macrophages, IL-1 mRNA was clearly induced. Induction of the IL-1 alpha gene seemed to require the recognition of class II MHC products on the macrophage because of the following observations: specific rather than third-party macrophages were responsive to the T blast but not to T cell-conditioned media; induction was blocked by an anti-Ia mAb; CD4+ rather than CD8+ blasts were active; and polyclonal Con A blasts were much less efficient than antigen-specific T cells. Our data indicate that the strongest signal for IL-1 production during the macrophage-T cell interaction occurs in the efferent limb of the response, after rather than before the formation of class II MHC-restricted T lymphoblasts.     

Human interleukin 1 induces interleukin 1 gene expression in human vascular smooth muscle cells

The recognition that cells of the vascular wall can secrete cytokines such as IL-1 suggests new mechanisms for initiating or sustaining inflammatory responses in blood vessels. We report that purified human monocyte-derived IL-1 or recombinant human IL-1 (rIL-1 beta and rIL-1 alpha) induce cultured human smooth muscle cells derived from veins or arteries to synthesize IL-1 beta mRNA and produce and release biologically active IL-1. rIL-1 beta also stimulated the production of PGE2 by smooth muscle cells. Exposure to rIL-1 beta (1-100 ng/ml), or rIL-1 alpha (0.01-10 ng/ml) increased IL-1 beta mRNA levels within 30 min. Actinomycin D (1 microgram/ml) prevented the induction of IL-1 beta mRNA by rIL-1. IL-1 alpha mRNA was detected in SMC treated with cycloheximide (1 microgram/ml) and rIL-1 beta, or cycloheximide alone. rIL-1 alpha and rIL-1 beta produced maximal levels of IL-1 beta mRNA after 4 h, and intracellular IL-1 biological activity after 6 h of exposure. Release of IL-1 activity in the extracellular medium began after 1 h of incubation with rIL-1 beta or rIL-1 alpha, and continued for up to 24 h. Anti-TNF antiserum that neutralized the biological activity of rTNF did not affect rIL-1-induced production of IL-1 beta mRNA or IL-1 release, suggesting that the release of TNF does not mediate these processes. Several experimental approaches indicated that the release of IL-1 by smooth muscle cells was not due to endotoxin contamination of the IL-1 preparations. Anti-IL-1 antiserum blocked the induction of smooth muscle cell IL-1 gene expression by rIL-1 beta. Polymyxin B did not prevent IL-1-induced IL-1 expression by these cells, but blocked the effect of endotoxin. Heat treatment destroyed the stimulatory capacity of rIL-1 beta, but did not affect the ability of bacterial endotoxin to induce IL-1 expression. The production of IL-1 by human vascular smooth muscle cells was not due to contamination of the cell cultures with blood monocytes, inasmuch as treatment with an antimonocyte antibody (anti-Mo2) and complement did not alter IL-1 beta mRNA content or the amount of IL-1 released from the cells in response to endotoxin, rIL-1 alpha, or rIL-1 beta.(ABSTRACT TRUNCATED AT 400 WORDS)     

Aberrant acute-phase response in aged interleukin-6 knockout mice

This study was designed to determine whether the acute-phase response in aged mice is altered by interleukin (IL) 6 deficiency. Young and aged wild-type (WT) and IL-6 knockout (KO) BALB/C female mice were injected with lipopolysaccharide (LPS; 1.5 microg/g body weight). After 24 h, aged IL-6 KO mice had an improved survival when compared with aged WT mice. Serum levels of IL-6 in aged WT animals given LPS were determined and, as expected, were significantly higher when compared with young LPS-treated WT animals (P<0.05). Serum levels of the acute-phase protein, serum amyloid A, were 50% lower in aged LPS-treated IL-6 KO mice relative to aged WT mice given LPS (P<0.001). In contrast, the induction of LPS-binding protein was not affected by age or IL-6 deficiency in LPS-treated animals. Circulating levels of corticosterone were markedly reduced in aged LPS-treated IL-6 KO mice relative to aged WT mice given LPS. These data indicate that IL-6 is an important contributor to the outcome of the acute-phase response of aged individuals challenged with endotoxin. We conclude that the absence of IL-6, a cytokine that contributes to the elevated basal proinflammatory state observed in aging, can improve the ability of aged mice to withstand an otherwise lethal challenge of bacterial endotoxin.     

Induction of high-affinity interleukin 1 receptor on human peripheral blood lymphocytes by glucocorticoid hormones

The in vitro effect of glucocorticoids (GCs) on IL-1-R expression of human PBMCs was investigated. Both physiological and pharmacological concentration ranges of GC increased the specific binding of 125I-labeled human rIL-1 alpha to PBMCs. This enhancement was specific for GC, since other steroid hormones, such as progesterone, 17 beta-estradiol, and testosterone failed to elevate the binding of 125I-IL-1 alpha to PBMCs. The effect was time dependent with maximal effect occurring 6 h after treatment and dose dependent with half-maximal effect elicited by 100 nM prednisolone. Scatchard plot analysis indicated that 125I-IL-1 alpha binding increased from approximately 100 IL-1-R per cell to 2 X 10(3) receptors per cell without a major change in affinity (Kd = 2.6 X 10(-10) M). The subpopulation of PBMCs induced by GC to express higher levels of IL-1-R consisted predominantly of B lymphocytes, but not T lymphocytes, large granular lymphocytes, or monocytes. GCs also induced the expression of IL-1-R on some other cell types, including normal human dermal fibroblasts and the human large granular lymphocyte cell line YT. Since cycloheximide and actinomycin D inhibited the induction of IL-1-R by GC, synthesis of both new RNA and protein seems to be required for IL-1-R induction. This study presents the first evidence of upregulation of the receptors for IL-1 by GC, and may account for the reported enhancement of in vitro and in vivo humoral immune responses by GCs.     

Defective inflammatory response in interleukin 6-deficient mice

Systemic and localized inflammation elicit a number of host responses which include fever, cachexia, hypoglycemia, and major changes in the concentration of liver plasma proteins. Interleukin 6 (IL-6) is considered an important mediator of the inflammatory response, together with IL-1 and tumor necrosis factor alpha (TNF-alpha). The purpose of this study was to unequivocally determine the role of IL-6 in these phenomena making use of IL-6-deficient mice that we have recently generated by gene targeting. We report here that in the absence of IL- 6, mice are unable to mount a normal inflammatory response to localized tissue damage generated by turpentine injection. The induction of acute phase proteins is dramatically reduced, mice do not lose body weight and only suffer from mild anorexia and hypoglycemia. In contrast, when systemic inflammation is elicited through the injection of bacterial lipopolysaccharide (LPS), these parameters are altered to the same extent both in wild-type and IL-6-deficient mice, demonstrating that under these conditions IL-6 function is dispensable. Moreover, we show that LPS-treated IL-6-deficient mice produce three times more TNF-alpha than wild-type controls, suggesting that increased TNF-alpha production might be one of the compensatory mechanisms through which a normal response to LPS is achieved in the absence of IL-6. We also show that corticosterone is normally induced in IL-6-deficient mice, demonstrating that IL-6 is not required for the activation of the hypothalamic-pituitary-adrenal axis. Our results reinforce the idea that different patterns of cytokines are involved in systemic and localized tissue damage, and identify IL-6 as an essential mediator of the inflammatory response to localized inflammation.     

Effect of protein depletion and short-term parenteral refeeding on the host response to interleukin 1 administration

Previous studies have demonstrated that protein malnutrition adversely affects the synthesis and release of interleukin 1 by monocytic cells. The purpose of this study was to investigate the protein and trace metal metabolism of severely protein-malnourished guinea pigs given exogenous interleukin 1 in the postabsorptive state or while concomitantly receiving total parenteral nutrition (TPN). Protein-depleted guinea pigs in the postabsorptive state failed to exhibit fever, granulocytosis, accelerated amino acid oxidation, or an acute-phase protein response after administration of interleukin 1 or endotoxin. However, a reduction in the serum concentration of zinc (P less than 0.05) and iron (P less than 0.05) was observed in the guinea pigs given interleukin 1, but not in those given endotoxin. The short-term (1 day) administration of TPN restored positive leucine balance (P less than 0.001) and reduced leucine release from protein breakdown (P less than 0.001). No other differences in the protein metabolism or trace metal response to interleukin 1 were observed as a result of short-term TPN feeding. Body temperatures of these malnourished guinea pigs given interleukin 1 and TPN became febrile or hypothermic depending on initial body temperatures. It is concluded that an attenuated capacity to synthesize interleukin 1 and a failure to mount an appropriate acute-phase protein response to exogenously administered interleukin 1 exist in this protein-malnourished animal model. Furthermore, this diminished protein response appears to be independent of short-term substrate provision because TPN for 1 day was unable to restore the full effects of the acute-phase response as mediated by interleukin 1.     

Multiple biological activities of human recombinant interleukin 1.

Complementary DNA coding for human monocyte interleukin 1 (IL-1), pI 7 form, was expressed in Escherichia coli. During purification, IL-1 activity on murine T cells was associated with the recombinant protein. Homogeneous human recombinant IL-1 (hrIL-1) was tested in several assays to demonstrate the immunological and inflammatory properties attributed to this molecule. hrIL-1 induced proliferative responses in a cloned murine T cell in the presence of suboptimal concentrations of mitogen, whereas no effect was observed with hrIL-1 alone. At concentrations of 0.05 ng/ml, hrIL-1 doubled the response to mitogen (5 X 10(6) half maximal units/mg). Human peripheral blood T cells depleted of adherent cells underwent a blastogenic response and released interleukin 2 in the presence of hrIL-1 and mitogen. hrIL-1 was a potent inflammatory agent by its ability to induce human dermal fibroblast prostaglandin E2 production in vitro and to produce monophasic (endogenous pyrogen) fever when injected into rabbits or endotoxin-resistant mice. These studies establish that the dominant pI 7 form of recombinant human IL-1 possesses immunological and inflammatory properties and acts on the central nervous system to produce fever.     

In vivo effects of interleukin-10 on human cytochrome P450 activity

BACKGROUND: Injection of lipopolysaccharide into human volunteers leads to an increase in serum interleukin-1beta, interleukin-6, and tumor necrosis factor-alpha and a significant decrease in cytochrome P450 (CYP)-mediated drug metabolism. The in vivo effects of the noninflammatory cytokine interleukin-10 (IL-10) on CYP-mediated drug metabolism was examined. METHODS: IL-10 (8 microg/kg) and placebo were administered for 6 days to 12 healthy volunteers in a double-blind crossover study. Tolbutamide (CYP2C9), caffeine (CYP1A2), dextromethorphan (CYP2D6 and CYP3A), and midazolam (CYP3A) were administered on days 4 and 5 to determine individual CYP activities. RESULTS: Few clinically apparent side effects were observed after administration of IL-10; however, blood chemistries reflected an acute-phase response. A significant drop in serum albumin (mean percentage change +/- SD between groups; 4.7% +/- 6.0%, P < or = .02), a significant increase in serum ferritin (736% +/- 717%, P < or = .001), and a significant reduction in platelet count (49% +/- 12%, P < or = .0001) was observed after administration of IL-10. IL-10 significantly (P < or = .02) decreased CYP3A activity 12% +/- 17%, as reflected by midazolam clearance. CYP2C9 activity was significantly (P < or = .005) increased by 38% +/- 35%, as reflected by the tolbutamide urinary metabolic ratio and oral clearance. However, administration of IL-10 resulted in a 40% increase in the fraction unbound of tolbutamide. Therefore no difference in the unbound clearance of tolbutamide was observed between placebo (23.3 +/- 9.7 L/h) or IL-10 (23.5 +/- 11.4 L/h) administration. No significant changes in either CYP1A2 or CYP2D6 activities were observed between placebo and treatment arms of the study. CONCLUSION: IL-10 administration resulted in an acute-phase response. Administration of IL-10 did not alter CYP1A2, CYP2C9, and CYP2D6 activities. CYP3A-mediated biotransformation was reduced by administration of IL-10.     

Antitumor activity of recombinant interleukin 6 in mice

IL-6 possesses multiple biologic activities that affect a broad range of cells including those directly involved in immune responses as well as cells important in the systemic response to infection or trauma. We now show that purified human rIL-6, when administered alone at relatively high doses that are comparable to therapeutic levels of IL-2, mediated substantial reductions in the number of pulmonary and hepatic micrometastases from four distinct syngeneic tumors. Unlike IL-2, IL-6 injections resulted in neither observable toxicity nor death of the treated mice at the dose regimens used. Host immunosuppression by sublethal total-body irradiation before the initiation of therapy prevented the IL-6 antitumor effect, thus suggesting that IL-6 acted through a radiosensitive host component rather than directly on the tumor itself. Moreover, the systemic administration of relatively low doses of IL-6 in combination with subtherapeutic doses of TNF to mice bearing an established weakly immunogenic, syngeneic tumor at a subcutaneous site resulted in marked tumor regression and cure rates. These studies represent the first demonstration of tumor regression mediated by recombinant IL-6 in vivo.     

Ceramide induces interleukin 6 gene expression in human fibroblasts

We previously reported that ceramide, the immediate product of sphingomyelin hydrolysis, increases in response to interleukin (IL)-1 beta and plays a role in modulating IL-1 beta-mediated prostaglandin E2 production and cyclooxygenase gene expression in human fibroblasts (Ballou, L. R., C. P. Chao, M. A. Holness, S. C. Barker, and R. Raghow. 1992. J. Biol. Chem. 267:20044-20050). Here we describe the effects of ceramide in another IL-1 beta-mediated process in these cells, the induction of IL-6 production. We found that submicromolar concentrations of C2-ceramide induced IL-6 gene expression and protein production as effectively as IL-1 beta. Both D-erythro-C2-ceramide (a cell-permeable analogue of natural ceramide) and D-threo-C2-ceramide were potent inducers of IL-6 production, while neither L isomer of ceramide was effective. Compared with IL-1 beta-induced IL-6 production, cells treated with ceramide or exogenous sphingomyelinase induced 82 and 50% of maximal IL-1 beta-induced IL-6 levels by 6 h, respectively; by 24 h all three treatments induced similar levels of IL- 6 production. Ceramide-induced IL-6 messenger RNA could be detected within 1 h of treatment and reached maximal levels by 24 h. These findings suggest that ceramide may play a role in the regulation of IL- 6 gene expression.