Zymosan-induced Generalized Inflammation Research Articles

Dexmedetomidine promotes inflammation resolving through TGF-β1 secreted by F4/80+Ly6G+ macrophage

Dexmedetomidine (DEX) is a highly selective α2-adrenoceptor agonist, which can regulate inflammatory responses. However, whether DEX interferes with the inflammation resolving remains unclear. Here, we reported the effects of DEX on zymosan-induced generalized inflammation in mice during resolution. Mice were administered intraperitoneally with DEX after the initiation of sepsis. The resolution interval (Ri), a vital resolution indice, decreased from twelve hours to eight hours after the administration of DEX. The induction of peritoneal pro-inflammatory interleukin [IL] - 1β and tumour necrosis factor-α (TNF-α) appeared to be inhibited. Of interest, the anti-inflammatory transforming growth factor-β1 (TGF-β1) but not IL-10 levels were up-regulated at twenty-four hours in the DEX group along with 1.0 mg/mice zymosan A (ZyA) treatment. The expression levels of multiple genes related to protective immune processes and clearance functions were detected and revealed the same trends. DEX markedly increased the F4/80+Ly6G+ macrophage population. Additionally, the adequate apoptotic neutrophil clearance from injury after DEX installation could be reverse by opsonization or co-instillation of TGF-β1 neutralizing antibody in vivo, promoting the inflammation-resolution programs. In conclusion, DEX post-treatment, via the increase of F4/80+Ly6G+ macrophages, provokes further secretion of TGF-β1, leading to the attenuated cytokine storm and accelerated inflammation resolving.

Protective effects of dioscin against systemic inflammatory response syndromevia adjusting TLR2/MyD88/NF‑κb signal pathway

Development of active compounds to control inflammation against systemic inflammatory response syndrome (SIRS) is critical important. Dioscin shows anti-inflammatory effects in our previous works. However, the action of the compound on SIRS still remained unknown. In the present paper, zymosan induced generalized inflammation (ZIGI) models in mice and rats, and PMA-differentiated THP‑1 cells stimulated by lipopolysaccharide (LPS) and Pam3-Cys-Ser-Lys4 (Pam3CSK4) were used. The results showed that dioscin significantly inhibited the proliferation of THP‑1 cells stimulated by LPS and Pam3CSK4, obviously reduced the soakage of inflammatory cells and necrosis in liver, kidney and intestine of rats and mice, and reduced peritoneal ascites fluid compared with ZIGI model groups. In addition, dioscin significantly declined the levels of alanine transaminase (ALT), aspartate transaminase (AST), creatinine (Cr), blood urea nitrogen (BUN), malondialdehyde (MDA) and myeloperoxidase (MPO), increased the levels of superoxide dismutase (SOD) in rats and mice. The migration of macrophages in tissues was also suppressed by dioscin. Mechanism investigation showed that dioscin significantly inhibited the expression levels of TLR2, MyD88, NF‑κb, HMGB‑1, increased the expression levels of IKBα, and decreased the mRNA levels of interleukin‑1 beta (IL‑1β), interleukin‑6 (IL‑6) and tumor necrosis factor‑alpha (TNF‑α) in liver, kidney, intestine tissues of rats and mice, and in PMA-differentiated THP‑1 cells, which were further confirmed by TLR2 siRNA silencing in vitro. In conclusion, our data confirmed that dioscin exhibited protective effects against SIRS via adjusting TLR2/MyD88 signal pathway, which should be developed as one potent candidate to treat SIRS in the future.

N-acetylcysteine Administration is Associated with Reduced Activation of NF-kB and Preserves Lung Dendritic Cells Function in a Zymosan-Induced Generalized Inflammation Model

In severe sepsis, functional impairment and decreased numbers of dendritic cells (DCs) are essential reasons for immune function paralysis, secondary organ infection, and organ failure. We investigated the effects of N-acetylcysteine (NAC) administration on protecting lung DCs function in a zymosan-induced generalized inflammation (ZIGI) model. ZIGI was initiated in 80 Balb/c mice by intraperitoneal injection of zymosan (ZYM; 900mg/kg). Mice were divided into 4 groups: (1) SHAM+Vehicle; (2) SHAM+NAC; (3) ZYM+Vehicle; and (4) ZYM+NAC. NAC (100mg/kg) was administered at different time after ZYM injection. After 48h, we assessed: lung tissue pathological changes; arterial blood gas values; purified lung DCs surface expressions of MHC-II/I-A(d) and co-stimulatory molecules CD80, CD83, and CD86; lung DCs mRNA levels of chemokine receptors CCR5 and CCR7; lung DCs apoptosis; lung DCs ultrastructure by transmission electron microscopy; lung DCs NF-kB transcription factor activity; and LPS-stimulated lung DCs in vitro production of IL-12 and IL-10 were examined. NAC treatment resulted in: significant improvements in ZYM-induced lung tissue damage and impaired lung function; inhibited lung DCs ZYM-induced increased expression of MHC-II/I-A(d), CD83, and CD86, but not CD80; reduced lung DCs ZYM-induced CCR5 and CCR7 mRNA levels; suppressed ZYM-induced lung DCs apoptosis; ameliorated ZYM-induced lung DCs ultrastructural abnormalities; inhibited ZYM-induced lung DCs NF-κB activity; and enhanced lung DCs production of IL-12 and inhibited their production of IL-10. Repeated injections of NAC during the early stage of severe sepsis effectively inhibited lung DCs activation and their apoptosis, which could preserve DCs function.

Activation of Cholinergic Anti-Inflammatory Pathway Contributes to the Protective Effects of 100% Oxygen Inhalation on Zymosan-Induced Generalized Inflammation in Mice

The 100% oxygen inhalation has been demonstrated to have a protective effect on mice with zymosan-induced generalized inflammation. However, the underlying mechanism is largely unknown. The present study was designed to explore the role of the cholinergic anti-inflammatory pathway in this animal model. Oxygen inhalation was given to mice at 4 and 12 h after zymosan injection. One group of mice underwent vagotomy 7 d before zymosan injection. The other two groups of mice either received nicotinic acetylcholine receptor (nAChR) antagonist mecamylamine, or α7 nicotinic acetylcholine receptor (α7nAChR) antagonist methyllycaconitine 30 min before oxygen was given. The 100% oxygen treatment significantly decreased the serum level of TNF-α and increased the serum level of IL-10. The pathologic changes of the heart, lung, liver, and kidney were attenuated, as well as the dysfunction of liver and kidney. The 7-d survival rate of zymosan-challenged mice was also improved. Conversely, all these protective effects caused by pure oxygen treatment were abolished in those animals that received anti-cholinergic treatments. The cholinergic anti-inflammatory pathway may be involved in the 100% oxygen protective mechanism against zymosan-induced generalized inflammation in mice.

β2-Adrenergic Receptor Antagonist Butoxamine Partly Abolishes the Protection of 100% Oxygen Treatment Against Zymosan-Induced Generalized Inflammation in Mice

We have demonstrated that 100% oxygen inhalation is beneficial to zymosan-induced generalized inflammation, and reactive oxygen species may be involved in the protection of oxygen treatment. Other investigators suggest that reactive oxygen species may modulate the sympathetic nervous system activity and β2-adrenergic receptor (β2AR)-mediated pathway. Moreover, studies have demonstrated that β2AR agonists are beneficial to sepsis. Therefore, we assessed the effects of β2AR antagonist butoxamine on the protection of oxygen treatment against zymosan-induced generalized inflammation in mice. Mice were given oxygen treatment by exposure to 100% oxygen for 3 h starting at 4 and 12 h after zymosan injection, respectively. In the mortality study, survival was monitored for 7 days after zymosan injection in mice. At 24 h after zymosan injection, mice were killed, and blood sample and organs were harvested for analysis. We observed that 100% oxygen treatment prevented the abnormal changes in organ histopathology, lactate dehydrogenase and C-reactive protein in serum, inflammatory cytokines in serum and tissue, and arterial blood gas analysis and improved the survival rate in zymosan-challenged mice. We found that pretreatment with β2AR antagonist butoxamine partly abolished the protection of 100% oxygen inhalation. We also showed that zymosan induced the increase in serum 3'-5'-cyclic adenosine monophosphate (cAMP) and the decrease in tissue cAMP. However, oxygen treatment increased the cAMP levels in both serum and tissue, which were partly abolished by pretreatment with butoxamine. Thus, 100% oxygen inhalation may protect against zymosan-induced generalized inflammation in mice partly through activation of β2AR pathway and subsequently enhance cAMP levels in both serum and tissue.

Hyperbaric oxygen therapy reduces the toll-like receptor signaling pathway in multiple organ failures.

Zymosan-induced generalized inflammation is the only experimental model that reproduces characteristics of human multiple organ dysfunction syndrome (MODS). Toll-like receptors (TLRs) are key components in innate immune responses and their signaling pathway is known to activate target genes such as nuclear factor-κB (NF-κB) and cytokines that are involved in inflammation and immune responses. We previously reported that hyperbaric oxygen (HBO) therapy is effective in the treatment of severe zymosan-induced inflammation in MODS. The aim of this study was to investigate the effect of HBO exposure on TLR2 and TLR4 signal transduction and organ dysfunction during MODS induced by zymosan in the rat. Male Wistar rats were randomized into four groups and treated as follows: (1) saline solution (control); (2) zymosan; (3) HBO 4 and 11h after zymosan injection; (4) HBO 4 and 11h after saline solution injection. Zymosan-induced damage of the lungs, liver, and small intestine was evaluated using histology and biochemistry. The activation of the TLR signaling pathway was measured with Western blot, reverse transcriptase polymerase chain reaction analysis (RT-PCR), and immunohistochemistry. Zymosan induced a severe inflammatory response characterized by the activation of the TLR signaling pathway and by an organ dysfunction. HBO exposure significantly reduced the development of lung, liver, and intestine injury in our experimental model. It also significantly reduced the zymosan-induced expression of TLR2 and TLR4, NF-κB activation, and cytokine production. Taken together, these results suggest that, by interfering with the TLR pathway, HBO treatment may exert a protective effect against tissue injury caused by zymosan-induced generalized inflammation.

Erythropoietin stimulates spleen BMP4-dependent stress erythropoiesis and partially corrects anemia in a mouse model of generalized inflammation

AbstractMouse bone marrow erythropoiesis is homeostatic, whereas after acute anemia, bone morphogenetic protein 4 (BMP4)–dependent stress erythropoiesis develops in the spleen. The aim of this work was to compare spleen stress erythropoiesis and bone marrow erythropoiesis in a mouse model of zymosan-induced generalized inflammation, which induces long-lasting anemia and to evaluate the ability of erythropoietin (Epo) injections to correct anemia in this setting. The effects of zymosan and/or Epo injections on erythroid precursor maturation and apoptosis, serum interferon-γ levels, hematologic parameters, and spleen BMP4 expression were analyzed, as well as the effect of zymosan on red blood cell half-life. We found that bone marrow erythropoiesis is suppressed by inflammation and does not respond to Epo administration, despite repression of erythroblast apoptosis. On the contrary, a robust erythropoietic response takes place in the spleen after Epo injections in both control and zymosan-induced generalized inflammation mice. This specific response implies Epo-mediated induction of BMP4 expression by F4/80+ spleen macrophages, proliferation of stress burst-forming units-erythroid, and increased number of spleen erythroblasts. It allows only partial recovery of anemia, probably because of peripheral destruction of mature red cells. It is not clear whether similar BMP4-dependent stress erythropoiesis can occur in human bone marrow after Epo injections.

Erythropoietin Injections Stimulate Spleen BMP4-Dependant Stress Erythropoiesis in a Mouse Model of Generalized Inflammation.

Abstract 1983Poster Board I-1005 Introduction:In mouse, acute anemia leads to the rapid expansion and differentiation of stress erythroid progenitors in the spleen. It has been shown that these progenitors respond to BMP4, Stem Cell Factor and hypoxia and differentiate into stress BFU-E. These are sensitive to high levels of erythropoietin (EPO) and rapidly expand in the spleen, allowing rapid recovery from the anemia (JM Perry et al., Blood 2009, 113:911-918). Inflammation is known to inhibit growth and differentiation of erythroid progenitors and to suppress EPO synthesis in the kidney. However, the effect of pro-inflammatory cytokines on this stress erythropoiesis response is not known. We have recently developed a mouse model of zymosan-induced generalized inflammation and shown that stimulation of erythropoiesis by repeated blood withdrawal or injections of erythropoietin favours iron mobilization from tissue iron stores (S. Lasocki et al., CCM 2008, 36:2388-2394), suggesting that EPO treatment may be beneficial provided effective erythropoiesis can be elicited. Objectives:The aim of our study was to assess the impact of EPO injections on the stress erythropoietic response in this mouse model of chronic inflammation. Methods:Mice (C57BL/6) received a single intraperitoneal injection of zymosan at day 1 (Z1) followed by four consecutive daily injections of EPO at day 5, 6, 7 and 8. Mice were analyzed one day (Z9EPO1), four days (Z12EPO4) or nine days (Z17EPO9) after the final injection and compared to controls, Z alone or EPO alone. Double Ter119/CD71 labelling was used to analyze the different stages of erythroblast differentiation by FACS, in bone marrow and spleen in the different conditions. Spleen BMP4 expression was followed by RT-qPCR and immunohistochemistry. Serum EPO levels were measured by ELISA and haematological parameters were recorded. Results:In the inflammatory condition, bone marrow erythropoiesis is suppressed and does not respond to EPO injections. There is a concomitant increased in the percentage of apoptotic Ter119+ cells. In the spleen, inflammation increases spleen size but only moderately stimulates the percentage of erythroblasts. However, EPO injections lead to a 10-fold increase in the percentage of immature erythroblasts at Z9EPO1, followed three days later (Z12EPO4) by a similar increase in the proportion of mature erythroblasts. This finally results in increased reticulocytes and haemoglobin concentration.In the spleen, BMP4 mRNAs are not stimulated by inflammation but significantly increased by EPO injections, both in normal mice and mice with Zymosan-induced inflammation. The protein BMP4 is expressed by erythroid precursors and stromal cells. Double labelling with F4/80 and BMP4 clearly shows that spleen macrophages are the BMP4-expressing cells following EPO injections in mice with a generalized inflammation. Conclusion:In mouse, bone marrow erythropoiesis is repressed by inflammation as it has been shown for human erythropoiesis and it does not respond to EPO injections. By contrast, spleen stress erythropoiesis is strongly stimulated by injections of EPO despite the presence of inflammation. This results from a strong increase in BMP4 synthesis by spleen macrophages. BMP4 is known to be stimulated by acute anemia but our study is the first report of a direct effect of EPO injections on BMP4 expression in the spleen and of the identification of macrophages as the stromal cells producing BMP4.It will be of interest to find out if bone marrow macrophages in humans can synthesize BMP4 and also contribute to a medullar stress erythropoietic response. Disclosures:No relevant conflicts of interest to declare.

Ethyl pyruvate reduces the development of zymosan-induced generalized inflammation in mice

Ethyl pyruvate (EP) is a simple aliphatic ester, which has been shown to have anti-inflammatory effects in previous numerous cell culture and animal studies. In the present study, we investigated the effects of EP (75 mg/kg i.p.) on the development of shock caused by zymosan. Prospective, randomized study. University-based research laboratory. Male CD mice. Mice received either intraperitoneally zymosan (500 mg/kg, administered i.p. as a suspension in saline) or vehicle (0.25 mL/mouse saline). EP (75 mg/kg i.p. was administered 1 and 6 hrs after zymosan administration. Organ failure and systemic inflammation in mice was assessed 18 hrs after administration of zymosan and/or EP. Treatment of mice with EP attenuated the peritoneal exudation and the migration of polymorphonuclear cells caused by zymosan. EP also attenuated the lung, liver, and pancreatic injury and renal dysfunction caused by zymosan as well as the increase in myeloperoxidase activity in the lung and intestine caused by zymosan. Immunohistochemical analysis for inducible nitric oxide synthase, nitrotyrosine, poly (ADP-ribose), tumor necrosis factor-alpha, and interleukin-1beta revealed positive staining in pancreatic and intestinal tissue obtained from zymosan-injected mice. The degree of staining for nitrotyrosine, inducible nitric oxide synthase, poly (ADP-ribose), tumor necrosis factor-alpha, and interleukin-1beta were markedly reduced in tissue sections obtained from zymosan-injected mice, which had received EP. In addition, administration of zymosan caused a severe illness in the mice characterized by a systemic toxicity, significant loss of body weight, and a 60% of mortality at the end of observation period (7 days). Treatment with EP significantly reduced the development of systemic toxicity, the loss in body weight, and the mortality (20%) caused by zymosan. This study provides evidence that EP attenuates the degree of zymosan-induced shock in mice.

Etoposide Attenuates Zymosan-Induced Shock in Mice

Zymosan-induced generalized inflammation is a convenient model to study the process of acute and chronic inflammatory processes resulting in multiple organ dysfunction syndrome. Macrophages as a source of many pro-inflammatory mediators are the major players in shock and further organ failure. Etoposide is a cytostatic drug known to reduce macrophages and monocytes in blood circulation. In the present study we have investigated whether the ability of etoposide to diminish macrophage number would have an impact on the course of zymosan-induced shock. The drug injected at a dose of 10 mg/kg 1 day before zymosan, significantly reduced the mortality and decreased the organ toxicity in Balb/c mice. Simultaneously, an inhibition of TNF-alpha production by alveolar and peritoneal macrophages was observed. Etoposide administered into mice with severe combined immunodeficiency (SCID) did not change the survival rate and had a little influence on organ toxicity. Our findings suggest that the beneficial action of etoposide might be attributed to the reduction of macrophages and alteration of their functions. Its effect depends on the presence of functional T and B lymphocytes. The results deserve further investigation of etoposide as a perspective therapeutic tool for inhibiting the excessive inflammatory response and to be helpful for revealing mechanisms of shock development.

Exogenous VIP limits zymosan-induced generalized inflammation (ZIGI) in mice

Vasoactive intestinal peptide (VIP) was administered in a model of zymosan-induced generalized inflammation (ZIGI). Its beneficial action was associated with reduced TNF-α and increased IL-10 production, lowered levels of creatinine, alanine aminotransferase (ALT), aspartate aminotransferase (AST) and bilirubin in circulation. VIP diminished the level of RANTES and MIP-1α in peritoneal exudate and circulation. The neuropeptide inhibited NO release from stimulated peritoneal macrophages. Decreased spleen, liver and kidney enlargement and less pathological changes in liver were observed. The effect of VIP was attenuated by pretreatment with VIP antagonist (anti-VIP) before the induction of shock.

ZYMOSAN-INDUCED GENERALIZED INFLAMMATION: EXPERIMENTAL STUDIES INTO MECHANISMS LEADING TO MULTIPLE ORGAN DYSFUNCTION SYNDROME

Patients suffering from multiple organ dysfunction syndrome (MODS) comprise a heterogeneous population, which complicates research in its pathogenesis. Elucidation of the mechanisms involved in the development of MODS will ultimately necessitate the collection of tissue samples and the performance of invasive procedures. These requirements greatly reduce the possibilities for research in human subjects. Therefore, an animal model for MODS is a necessary and valuable tool. In the mid 1980s, the zymosan-induced generalized inflammation (ZIGI) model was introduced. Intraperitoneal injection of zymosan in mice or rats leads, in the course of 1 to 2 weeks, to increasing organ damage and dysfunction. The ZIGI model has been recognized as the one that best resembles human MODS and it has been used widely to study systemic inflammation in relation to organ failure. This review describes the ZIGI model and gives an overview of the results obtained.

The role of tumor necrosis factor in the development of multiple organ failure in a murine model

To elucidate the role of tumor necrosis factor (TNF) in the development of multiple organ dysfunction syndrome (MODS) after zymosan-induced peritonitis in mice. Prospective controlled laboratory study on zymosan-induced generalized inflammation in mice. Over < or =28 days, a single intraperitoneal administration of zymosan induced a three-phase illness in C57BL mice, rendering them very ill with MODS-like symptoms from day 7 onward. Additionally, the same experiment was performed on C57BL/6 TNF-Rc-p55 knockout mice to elucidate the role of TNF and its receptor p55. Animal research laboratory. Inbred C57BL mice and C57BL p55-/- mice received a single sterile intraperitoneal injection of zymosan suspended in paraffin oil (0.75 mg/g of body weight). The animals were monitored for survival, condition, and body weight for < or =28 days. At 3, 7, 14, and 28 days after zymosan administration, bronchoalveolar lavage was performed and lungs and livers were extracted for isolation of RNA and histopathologic evaluation. Reverse-transcriptase-polymerase chain reaction was performed to quantify TNF-alpha messenger RNA (mRNA) in the respective organs. Both animal strains went through initial shock with a high mortality rate during the first 3 days. The C57BL mice developed MODS with typical symptoms and histopathologic results correlating with excessive TNF-alpha mRNA expression from day 7 onward. In contrast, no disease, histopathologic changes, nor TNF-alpha mRNA expression in liver or lung was found within the TNF-Rc-p55-/- mice. Organ-derived TNF-alpha plays a crucial role in the development of MODS in this murine model.

Striated muscle microvascular response to zymosan-induced generalized inflammation in awake hamsters.

The effect of zymosan-induced generalized inflammation on the microcirculation of distant striated skin muscle was studied for a 12 day period in awake Syrian golden hamsters (n = 18) using the dorsal skinfold chamber model and intravital fluorescence microscopy. Intraperitoneal zymosan exposure (125 mg/100 g body weight) induced significant nutritive perfusion failure in the distant striated muscle tissue at Day 1 without complete recovery over the 12 day observation period, as indicated by the marked reduction of functional capillary density when compared with both baseline values and values of sham-treated control animals. Moreover, intraperitoneal zymosan exposure induced endothelial disintegration, as demonstrated by the continuous increase of macromolecular leakage throughout the 12 days of observation. Strikingly, zymosan did not induce significant leukocyte adherence to the endothelial lining of postcapillary and collecting venules of the striated muscle tissue. Thus, we conclude that in this model of generalized inflammation nutritive perfusion failure and loss of endothelial integrity in distant striated muscle is not mediated by activated leukocytes, but must rather be attributed to direct toxic effects of mediators, elicited by the local (intraperitoneal) zymosan challenge and systemically released.

Chlorpromazine down-regulates tumor necrosis factor-alpha and attenuates experimental multiple organ dysfunction syndrome in mice.

Chlorpromazine is a known modulator of tumor necrosis factor (TNF)-alpha production. TNF-alpha is thought to be a key mediator in the development of the multiple organ dysfunction syndrome (MODS). We investigated the effect of chlorpromazine on the development of zymosan-induced MODS in mice and on plasma TNF-alpha concentrations and production capacity of TNF-alpha by peritoneal cells. Prospective, controlled laboratory study on zymosan-induced generalized inflammation in mice. Animal research laboratory. C57BL/6 mice received daily doses (4 mg/kg body weight) of chlorpromazine, beginning 2 days before or 5 days after zymosan administration. In additional groups, the daily chlorpromazine dose of 4 mg/kg started 5 days after zymosan was increased 2 days later to 8 or 16 mg/kg/day. The animals were monitored for survival, condition, body weight, and body temperature. Twelve days after zymosan was administered, all surviving animals were killed to obtain plasma, organs, and peritoneal cells. Plasma concentrations of TNF-alpha and lipopolysaccharide-stimulated production of TNF-alpha by peritoneal cells were measured. Organ weights were recorded as an indicator for organ damage. Although survival was not improved when the animals were treated with chlorpromazine, the chlorpromazine-treated survivors showed improved body weight and temperature when compared with the animals receiving zymosan only. Also, the organ weights and lung damage improved significantly in the treated group. Chlorpromazine was most effective when started before zymosan administration. When administered afterward, clinical improvement declined with the dose. In all cases, circulating TNF-alpha and production of TNF-alpha by peritoneal macrophages were lowered toward control values. Chlorpromazine mitigates the development of zymosan-induced MODS, possibly by reducing macrophage TNF-alpha production.

Inflammatory cytokines in an experimental model for the multiple organ dysfunction syndrome

To investigate the alterations in circulating pro-inflammatory cytokines and cytokine production by peritoneal macrophages during the development of multiple organ dysfunction syndrome. Prospective, controlled laboratory study on zymosan-induced generalized inflammation in mice. Single intraperitoneal administration of zymosan induces, over a 12-day period, a triphasic illness in mice; the third phase, from day 6 onward, resembles multiple organ dysfunction syndrome. Animal research laboratory. C57BL/6CRW mice received a single intraperitoneal dose of zymosan on day 0, and standard numbers of animals were killed at different time points up until day 12. Plasma concentrations of interleukin (IL)-1 alpha and IL-1 beta, IL-6, and tumor necrosis factor (TNF)-alpha were measured from 3 hrs to 12 days after administration of zymosan. At the same time points, both lipopolysaccharide-stimulated and unstimulated production of these cytokines by peritoneal macrophages were measured in vitro. Plasma TNF and IL-6 concentrations transiently increased during the first 24 hrs after administration of zymosan. After 8 days, a prominent peak of biologically inactive TNF was observed. Both unstimulated and lipopolysaccharide-stimulated cytokine production by peritoneal cells showed profound changes during the experimental period. These findings seem to confirm our hypothesis that the macrophages are in a continuously activated state and altered in their function, when the animals develop multiple organ dysfunction syndrome. Further studies are needed to elucidate what happens with these cytokines at the tissue level, to better understand the pathophysiology of multiple organ dysfunction syndrome.