The role of prostaglandin E2 in immune suppression following injury

Innate Immune System Response to Burn Damage-Focus on Cytokine Alteration

In the literature, burns are understood as traumatic events accompanied by increased morbidity and mortality among affected patients. Their characteristic feature is the formation of swelling and redness at the site of the burn, which indicates the development of inflammation. This reaction is not only important in the healing process of wounds but is also responsible for stimulating the patient’s innate immune system. As a result of the loss of the protective ability of the epidermis, microbes which include bacteria, fungi, and viruses have easier access to the system, which can result in infections. However, the patient is still able to overcome the infections that occur through a cascade of cytokines and growth factors stimulated by inflammation. Long-term inflammation also has negative consequences for the body, which may result in multi-organ failure or lead to fibrosis and scarring of the skin. The innate immune response to burns is not only immediate, but also severe and prolonged, and some people with burn shock may also experience immunosuppression accompanied by an increased susceptibility to fatal infections. This immunosuppression includes apoptosis-induced lymphopenia, decreased interleukin 2 (IL-2) secretion, neutrophil storm, impaired phagocytosis, and decreased monocyte human leukocyte antigen-DR. This is why it is important to understand how the immune system works in people with burns and during infections of wounds by microorganisms. The aim of this study was to characterize the molecular pathways of cell signaling of the immune system of people affected by burns, taking into account the role of microbial infections.

Effectiveness of ω-3 Polyunsaturated Fatty Acids Based Lipid Emulsions for Treatment of Patients after Hepatectomy: A Prospective Clinical Trial

Objective: The present study aimed to investigate the effectiveness of parenteral nutritional support with ω-3 PUFAs–based lipid emulsions in patients after liver resection. Methods: A total of 119 patients were randomly assigned to the immunonutrition (IM) group (n = 59) and control group (n = 60). The IM group was continuously given Omegaven^® 10% 100 mL/day rather than regular nutrition for five days postoperatively. Venous blood samples were obtained from all subjects before surgery and D1, D3 and D7 after surgery. Results: No significant difference was found in baseline characteristics of the two groups. On D1 after surgery, no statistically significant differences were observed in the blood sample tests between the two groups. On D3 after surgery, the levels of white blood cell count (WBC), alanine aminotransferase (ALT), aspartate transaminase (AST) and total bilirubin (TBil) were dramatically decreased in the IM group (t = 3.065, p = 0.003; t = 2.149, p = 0.034; t = 5.313, p= 0.001; and t = 2.419, p = 0.017, respectively). Furthermore, on D7 after surgery, not only could a significant decrease be observed in the IM group concerning the levels of WBC, ALT and TBil (t = 3.025, p = 0.003; t = 2.094, p = 0.038; and t = 2.046, p = 0.043, respectively), but it was also seen in the level of Δprothrombintime (PT) (t = 2.450, p = 0.016). An increase in the level of prealbumin (Pre-Alb) in the IM group was observed on D7 after surgery (t = 2.237, p = 0.027). The frequency of total complications in the IM group were significantly lower than in the control group (χ² = 4.225, p = 0.040 and χ² = 3.174, p = 0.075). The trend favored the IM group in reducing the total infective complications rate (χ² = 3.174, p = 0.075). A significant decrease in the duration of the hospital stay after surgery was also observed in the IM group (t = 2.012, p = 0.047).Conclusion: ω-3 PUFAs–based lipid emulsions for treatment of patients after hepatectomy are safe and effective in controlling inflammation, protecting liver function, and consequently reducing the rate of total complications and the duration of the hospital stay.

Omega-3 Fatty Acids in Modern Parenteral Nutrition: A Review of the Current Evidence

Intravenous lipid emulsions are an essential component of parenteral nutrition regimens. Originally employed as an efficient non-glucose energy source to reduce the adverse effects of high glucose intake and provide essential fatty acids, lipid emulsions have assumed a larger therapeutic role due to research demonstrating the effects of omega-3 and omega-6 polyunsaturated fatty acids (PUFA) on key metabolic functions, including inflammatory and immune response, coagulation, and cell signaling. Indeed, emerging evidence suggests that the effects of omega-3 PUFA on inflammation and immune response result in meaningful therapeutic benefits in surgical, cancer, and critically ill patients as well as patients requiring long-term parenteral nutrition. The present review provides an overview of the mechanisms of action through which omega-3 and omega-6 PUFA modulate the immune-inflammatory response and summarizes the current body of evidence regarding the clinical and pharmacoeconomic benefits of intravenous n-3 fatty acid-containing lipid emulsions in patients requiring parenteral nutrition.

Gingival crevicular fluid as a periodontal diagnostic indicator- II: Inflammatory mediators, host-response modifiers and chair side diagnostic aids

There has been a steady growing trend during the last few decades to develop tools to monitor periodontitis, in the field of oral disease diagnosis. Since GCF has the chance of being closely approximated to the periodontal tissues where periodontal disease begins, it seems to provide more information than markers in saliva. In response to bacterial infection, host production of inflammatory mediators, may be the trigger for periodontal disease progression. Existing paradigms in the biology of periodontitis have supported the detection of elevated levels of these mediators in GCF. This article is the Part II of the review that deals with inflammatory mediators and host-response modifiers as the potential biomarkers present in gingival crevicular fluid (GCF) and the chair side point-of-care diagnostic aids applicable to monitor periodontal inflammation.

Mechanistic aspects of inducible nitric oxide synthase-induced lung injury in burn trauma

INTRODUCTION

Although the beneficial effects of inducible nitric oxide synthase (iNOS) inhibition in acute lung injury secondary to cutaneous burn and smoke inhalation were previously demonstrated, the mechanistic aspects are not completely understood. The objective of the present study is to describe the mechanism(s) underlying these favourable effects. We hypothesised that iNOS inhibition prevents formation of excessive reactive nitrogen species and attenuates the activation of poly(ADP) (poly(adenosine diphosphate)) ribose polymerase, thus mitigating the severity of acute lung injury in sheep subjected to combined burn and smoke inhalation.

METHODS

Adult ewes were chronically instrumented for a 24-h study and allocated to groups: sham: not injured, not treated, n = 6; control: injured, not treated, n = 6; and BBS-2: injured treated with iNOS dimerisation inhibitor BBS-2, n = 6. Control and BBS-2 groups received 40% total body surface area 3rd-degree cutaneous burn and cotton smoke insufflation into the lungs under isoflurane anaesthesia.

RESULTS

Treatment with iNOS inhibitor BBS-2 significantly improved pulmonary gas exchange (partial pressure of oxygen in the blood/fraction of inspired oxygen (PaO₂/FiO₂) 409 ± 43 mmHg vs. 233 ± 50 mmHg in controls, p < 0.05) and reduced airway pressures (peak pressure 20 ± 1 cm H₂O vs. 28 ± 2 cm H₂O in controls, p < 0.05) and lung water content (lung wet-to-dry ratio 4.1 ± 0.3 vs. 5.2 ± 0.2 in controls, p < 0.05) 24h after the burn and smoke injury. BBS-2 significantly reduced the increases in lung lymph nitrite/nitrate (10 ± 3 μM vs. 26 ± 6 μM in controls, p < 0.05) and 3-nitrotyrosine (109 ± 11 (densitometry value) vs. 151 ± 18 in controls, p < 0.05). Burn/smoke-induced increases in lung tissue nitrite/nitrate, poly(ADP)ribose polymerase, nuclear factor-κB (NF-κB) activity, myeloperoxidase activity and malondialdehyde formation and interleukin (IL)-8 expression were also attenuated with BBS-2.

CONCLUSIONS

The results provide strong evidence that BBS-2 ameliorated acute lung injury by inhibiting the inducible nitric oxide synthase/reactive nitrogen species/poly(ADP-ribose) polymerase (iNOS/RNS/PARP) pathway.

Substance P upregulates cyclooxygenase-2 and prostaglandin E metabolite by activating ERK1/2 and NF-kappaB in a mouse model of burn-induced remote acute lung injury

Acute lung injury (ALI) is a major cause of mortality in burn patients, even without direct inhalational injury. Identification of early mediators that instigate ALI after burn and of the molecular mechanisms by which they work are of high importance but remain poorly understood. We previously reported that an endogenous neuropeptide, substance P (SP), via binding neurokinin-1 receptor (NK1R), heightens remote ALI early after severe local burn. In this study, we examined the downstream signaling pathway following SP-NK1R coupling that leads to remote ALI after burn. A 30% total body surface area full-thickness burn was induced in male BALB/c wild-type (WT) mice, preprotachykinin-A (PPT-A) gene-deficient mice, which encode for SP, and PPT-A(-/-) mice challenged with exogenous SP. Local burn injury induced excessive SP-NK1R signaling, which activated ERK1/2 and NF-κB, leading to significant upregulation of cyclooxygenase (COX)-2, PGE metabolite, and remote ALI. Notably, lung COX-2 levels were abrogated in burn-injured WT mice by L703606, PD98059, and Bay 11-7082, which are specific NK1R, MEK-1, and NF-κB antagonists, respectively. Additionally, burn-injured PPT-A(-/-) mice showed suppressed lung COX-2 levels, whereas PPT-A(-/-) mice injected with SP showed augmented COX-2 levels postburn, and administration of PD98059 and Bay 11-7082 to burn-injured PPT-A(-/-) mice injected with SP abolished the COX-2 levels. Furthermore, treatment with parecoxib, a selective COX-2 inhibitor, attenuated proinflammatory cytokines, chemokines, and ALI in burn-injured WT mice and PPT-A(-/-) mice injected with SP. To our knowledge, we show for the first time that SP-NK1R signaling markedly elevates COX-2 activity via ERK1/2 and NF-κB, leading to remote ALI after burn.

The 2008 ESPEN Sir David Cuthbertson Lecture: Fatty acids and inflammation--from the membrane to the nucleus and from the laboratory bench to the clinic

Many chronic conditions involve excessive inflammation that is damaging to host tissues. Excessive or inappropriate inflammation and immunosuppression are components of the response to surgery, trauma, injury and infection in some individuals and these can lead, progressively, to sepsis and septic shock. Hyperinflammation is characterised by the production of inflammatory cytokines, eicosanoids and other inflammatory mediators, while the immunosuppression is characterised by impairment of antigen presentation and of certain T cell responses. N-6 fatty acids may contribute to the hyperinflamed and immunosuppressed states. N-3 fatty acids from fish oil decrease the production of inflammatory cytokines and eicosanoids. They act both directly (by replacing arachidonic acid as an eicosanoid precursor) and indirectly (by altering the expression of inflammatory genes through effects on transcription factor activation). Thus, these fatty acids are potentially useful anti-inflammatory agents and may be of benefit in patients with chronic inflammatory diseases or at risk of hyperinflammation and sepsis. An emerging application of n-3 fatty acids is in surgical or critically ill patients where they may be added to parenteral or enteral formulas. Studies to date are suggestive of clinical benefits from these approaches, although more robust data are needed especially in critically ill patients.

Pathoanatomy and clinical correlates of the immunoinflammatory response following orthopaedic trauma

The natural inflammatory response to major trauma may be associated with the development of a systemic inflammatory state, remote multiorgan failure, and death. Although a controlled inflammatory response is beneficial, an exaggerated response can cause serious adverse systemic effects. Early identification of high-risk patients, based on inflammatory markers and genomic predisposition, should help direct intervention in terms of surgical stabilization and biologic response modification. Currently, two markers of immune reactivity, interleukin-6 and human leukocyte antigen-DR class II molecules, appear to have the most potential for regular use in predicting the clinical course and outcome in trauma patients; however, the ability to measure markers of inflammation is still limited at many hospitals. With improving technology and increasing research interest, understanding of the significance of the immunoinflammatory response system in injured patients will continue to evolve.

Deregulation of Tpl2 and NF-kappaB signaling and induction of macrophage apoptosis by the anti-depressant drug lithium

Lithium is an anti-depressant drug that also possesses immunomodulatory functions. The anti-inflammatory effect of lithium is thought to involve activation of the transcription factor CREB, although the underlying mechanism is incompletely understood. We show here that in macrophages lithium stimulates Tpl2, a MAP kinase kinase kinase (MAP3K) known to mediate activation of extracellular signal regulated kinase (ERK) and the downstream target CREB. Lithium activates Tpl2 by inducing degradation of p105, an NF-kappaB precursor protein that functions as a physiological inhibitor of Tpl2. This novel function of lithium does not involve inhibition of a well-characterized lithium target, GSK3beta, since other known GSK3beta inhibitors do not induce p105 degradation or Tpl2 activation. Lithium also promotes the activation of Tpl2 and ERK by the TLR4 ligand LPS. On the other hand, prolonged incubation of macrophages with lithium results in dramatic loss of p105 and inhibition of LPS-stimulated NF-kappaB activation. Consequently, lithium both attenuates LPS-mediated pro-inflammatory gene induction and induces apoptosis in macrophages. These results provide novel insight into the anti-inflammatory function of lithium.

Immunonutrition in surgical and critically ill patients

Surgery, trauma, burns and injury induce an inflammatory response that can become excessive and damaging in some patients. This hyperinflammation can be followed by an immunosuppressed state which increases susceptibility to infection. The resulting septic syndromes are associated with significant morbidity and mortality. A range of nutrients are able to modulate inflammation (and the associated oxidative stress) and to maintain or improve immune function. These include several amino acids, antioxidant vitamins and minerals, long-chain n-3 fatty acids and nucleotides. Experimental studies support a role for each of these nutrients in surgical, injured or critically ill patients. There is good evidence that glutamine influences immune function in such patients and that this is associated with clinical improvement. Evidence is also mounting for the use of long-chain n-3 fatty acids in surgical and septic patients, but more evidence of clinical efficacy is required. Mixtures of antioxidant vitamins and minerals are also clinically effective, especially if they include selenium. Their action appears not to involve improved immune function, although an anti-inflammatory mode of action has not been ruled out. Enteral immunonutrient mixtures, usually including arginine, nucleotides and long-chain n-3 fatty acids, have been used widely in surgical and critically ill patients. Evidence of efficacy is good in surgical patients. However whether these same mixtures are beneficial, or should even be used, in critically ill patients remains controversial, since some studies show increased mortality with such mixtures. There is a view that this is due to a high arginine content driving nitric oxide production.

Burn-induced immunosuppression: attenuated T cell signaling independent of IFN-gamma- and nitric oxide-mediated pathways

Burn injury results in immunosuppression; previous work implicated a combination of altered T lymphocyte subpopulations and the elaboration of macrophage-derived mediators. However, the conclusions were based on T cell stimulations in the setting of high-dose polyclonal mitogenic stimuli and a single kinetic time-point. In this study, splenocytes from burned animals were used to examine lymphocyte responses over a multi-day time course following saturating and subsaturating anti-CD3, as well as mixed lymphocyte response (MLR) stimulation. Burn injury resulted in suppressed splenocyte-proliferative responses to high-dose anti-CD3 (2 microg/ml) at all culture time-points (Days 2-5); this inhibition was eliminated by removing macrophages from the splenocyte cultures, by blocking NO production, or by using splenocytes from burned animals congenitally deficient in IFN-gamma (IFN-gamma(-/-)). The results are consistent with immunosuppression attributable to burn-induced IFN-gamma production, which in turn, drives macrophage NO synthesis (NOS). In MLR cultures, lymphocyte proliferation and IFN-gamma production were depressed at later time-points (Days 3-5). APC from burned animals showed no defects as MLR stimulators; T cells from burned animals showed defective, proliferative responses, regardless of the stimulator population. Removing macrophages, adding a NOS inhibitor, or using IFN-gamma(-/-) splenocytes did not restore the MLR response of burned splenocytes. T cells from burned IFN-gamma(-/-) animals also showed depressed proliferation with subsaturating levels of anti-CD3 (0.1 microg/ml); anti-CD-28 augmented the proliferative response. We conclude that burn-induced immunosuppression to authentic antigenic stimulation is related at least in part to defective CD3 signaling pathways and not simply to increased IFN-gamma or NO production.

Use of fish oil in parenteral nutrition: Rationale and reality

Excessive or inappropriate inflammation and immunosuppression are components of the response to surgery, trauma, injury and infection in some individuals and can lead, progressively, to sepsis and septic shock. The hyperinflammation is characterised by the production of inflammatory cytokines, arachidonic acid-derived eicosanoids and other inflammatory mediators, while the immunosuppression is characterised by impairment of antigen presentation and of T-helper lymphocyte type-1 responses. Long-chain n-3 fatty acids from fish oil decrease the production of inflammatory cytokines and eicosanoids. They act both directly (by replacing arachidonic acid as an eicosanoid substrate and by inhibiting arachidonic acid metabolism) and indirectly (by altering the expression of inflammatory genes through effects on transcription factor activation). Thus, long-chain n-3 fatty acids are potentially useful anti-inflammatory agents and may be of benefit in patients at risk of hyperinflammation and sepsis. As a consequence, an emerging application for n-3 fatty acids, in which they may be added to parenteral (or enteral) formulas, is in surgical or critically-ill patients. Parenteral nutrition that includes n-3 fatty acids appears to preserve immune function better than standard formulas and appears to diminish the extent of the inflammatory response. Studies to date are suggestive of clinical benefits from these approaches, especially in patients post surgery, although evidence of clinical benefit in patients with sepsis is emerging.

Antenatal administration of Rh-immune globulin causes significant increases in the immunomodulatory cytokines transforming growth factor-β and prostaglandin E2

BACKGROUND

Production of specific cytokines in response to administration of Rh-immune globulin (RhIG) was examined to assess the mechanism of inhibition of the anti-D production and prevention of hemolytic disease of the newborn (HDN).

STUDY DESIGN AND METHODS

Plasma levels of 17 different cytokines before and 48 hours after antenatal administration of anti-D were measured in 10 women candidates for prophylaxis with RhIG.

RESULTS

No striking changes were observed in levels of the cytokines interleukin (IL)-1 sRII, IL-12 p40, IL-16, or monocyte chemoattractant protein-1. Levels of IL-4, -5, -10, -13, and -17; macrophage inflammatory protein-1alpha; granulocyte-macrophage-colony-stimulating factor; tumor necrosis factor-beta; and interferon-gamma remained below detection levels both before and after testing. IL-1ra levels, however, showed a slight to moderate decrease in 7 of 10 women after RhIG administration. In contrast, levels of TGF-beta1 increased more than 1.3-fold in 7 of 10 women and more than 2-fold in 4 of 10 women; in 1 instance the increase was more than 5-fold and this woman also had a significant increase in TGF-beta2. In addition to TGF-beta, 5 of 10 women had a modest increase (>1.5-fold) in prostaglandin E2 (PGE2). Analyses of the combined results of the 10 women showed that increases in both TGF-beta1 and PGE2 after RhIG were significant.

CONCLUSION

These results indicate that RhIG prophylaxis can induce higher than baseline levels of two strongly immunomodulatory cytokines, TGF-beta and PGE2. These findings represent one possible mechanism for the inhibition of the primary immune response to the D antigen in women receiving RhIG prophylaxis for prevention of HDN.

The immunological consequences of injury

Immediate and early trauma death rates are determined by "first hits" such as hypoxia, hypotension and organ injury, while late mortality correlates closely with "second hits" such as infection. An imbalance between the early systemic inflammatory response (SIRS), and the later compensatory counter-inflammatory response (CARS), is considered to be responsible for much post-traumatic morbidity and mortality. From a clinical perspective, this remains a significant healthcare problem, which has stimulated decades of experimental and clinical research aimed at understanding the functional effects of injury on the immune system. This review describes the impact of injury on the innate and adaptive immune systems. Though it is worth noting that the features of the immune response to injury overlap in many areas with immune dysregulation in sepsis, we attempt here to elucidate the mechanism by which injury predisposes to infection rather than to describe the alterations in host immunity consequent to established sepsis.

PARENTERAL N-3 FATTY ACIDS MODULATE INFLAMMATORY AND IMMUNE RESPONSE IN RATS UNDERGOING TOTAL GASTRECTOMY

This study investigated the effect of n-3 fatty acid (FA)-containing parenteral nutrition on the circulatory lymphocyte subpopulation, intracellular cytokine and leukocyte adhesion molecule expression, and phagocytic activity in rats undergoing total gastrectomy. Normal rats with internal jugular catheters were assigned to normal control (NC) and two experimental groups and received total parenteral nutrition (TPN). At the same time, a total gastrectomy was performed in the experimental groups, whereas the NC group underwent a sham operation. The TPN solutions were isonitrogenous and identical in nutrient compositions except for differences in fat emulsion contents. The NC and one of the experimental groups received a soybean oil emulsion (SO), and the other experimental group received 50% soybean oil and 50% fish oil emulsion (FO). Half of the rats in each respective group were sacrificed 1 or 3 days after surgery or the sham operation to examine their immune response. The results showed that the FO group had a higher CD4 proportion and CD4/CD8 ratio than those of the SO and NC groups postoperatively. The phagocytic activity of peritoneal macrophages was higher in the FO group than in the NC group, but no difference was found between the SO and NC groups 3 days after surgery. The intracellular interferon (IFN)-gamma distribution in the FO group was higher than that of the SO group on postoperative days. Leukocyte adhesion molecule expressions and peritoneal monocyte chemotactic protein-1 levels were lower in the FO group than in the SO group on postoperative day 3. These results suggest that parenterally infused FO did not result in immunosuppression. In addition, FO administration promotes lymphocyte Th1 cytokine production, enhances peritoneal macrophage phagocytic activity, and reduces leukocyte adhesion molecule expression in rats with total gastrectomy.

Effect of prostaglandin E2 on PMA-induced macrophage differentiation

Major trauma such as severe bums and extensive surgery could result in accelerated macrophage differentiation and hyperactivation causing an excessive release of proinflammatory cytokines and prostaglandin E2 (PGE2) with consequent severe impairment of immunologic reactivity. HL-60 cells stimulated with phorbol 12-myristate 13-acetate (PMA) have been used as a model to asses the PGE2 role in the macrophage differentiation observed after major trauma. Cell adhesion, matrix metalloproteinase-9 (MMP-9) and tumor necrosis factor-alpha (TNF-alpha) production were measured after 24 h of PMA treatment in the presence of PGE2 (1 nM - 1 microM). PGE2 increased both the PMA-induced cell adhesion and MMP-9 production via EP2/EP4 receptors while it had no effect on the induced TNF-alpha release. The cAMP/PKA pathway, usually linked to EP2/EP4 activation, was not involved in the phenomenon, suggesting that an alternative signalling pathway could be linked to a PKC-activated enzyme. In fact PGE2 activity was partially inhibited by Wortmannin, a phosphoinositide-3 kinase (PI-3K) inhibitor indicating that PGE2 act as a co-factor able to increase macrophage differentiation in vitro via a PI-3K dependent pathway that could be also involved in the immunosuppression observed in the aftermath of trauma.

Enhanced expression of cyclooxygenase-2 and prostaglandin E2 in response to endotoxin after trauma is dependent on MAPK and NF-kappaB mechanisms

Macrophage prostaglandin E2 (PGE2) production is important in cellular immune suppression and in affecting the potential development of sepsis after trauma. We hypothesized that macrophage PGE2 production after trauma is regulated by mitogen-activated protein kinase (MAPK) and nuclear factor kappa B (NF-kappaB). Mice were subjected to trauma and splenic macrophages isolated 7 days later. Macrophages from traumatized mice showed increased cyclooxygenase-2 (COX-2) mRNA, protein expression, and PGE2 production compared with controls. Increased phosphorylation of extracellular signal-regulated kinase (ERK), c-jun N-terminal kinase (JNK), and p38 kinase was observed in macrophages from traumatized mice. Pharmacologic inhibition of MAPK blocked trauma-induced COX-2 expression, and PGE2 production. Trauma macrophages showed increased IkappaBalpha phosphorylation and NF-kappaB binding to DNA. Inhibiting IkappaBalpha blocked trauma-induced NF-kappaB activity, COX-2 expression and PGE2 production. This suggests that trauma-induced PGE2 production is mediated through MAPK and NF-kappaB activation and offers potential for modifying the macrophages' responses following injury.

n-3 fatty acids, inflammation, and immunity--relevance to postsurgical and critically ill patients

Excessive or inappropriate inflammation and immunosuppression are components of the response to surgery, trauma, injury, and infection in some individuals and these can lead, progressively, to sepsis and septic shock. The hyperinflammation is characterized by the production of inflammatory cytokines, arachidonic acid-derived eicosanoids, and other inflammatory mediators, while the immunosuppression is characterized by impairment of antigen presentation and of T helper cell type-1 responses. Long-chain n-3 FA from fish oil decrease the production of inflammatory cytokines and eicosanoids. They act both directly (by replacing arachidonic acid as an eicosanoid substrate and by inhibiting arachidonic acid metabolism) and indirectly (by altering the expression of inflammatory genes through effects on transcription factor activation). Thus, long-chain n-3 FA are potentially useful anti-inflammatory agents and may be of benefit in patients at risk of developing sepsis. As such, an emerging application of n-3 FA is in surgical or critically ill patients where they may be added to parenteral or enteral formulas. Parenteral or enteral nutrition including n-3 FA appears to preserve immune function better than standard formulas and appears to partly prevent some aspects of the inflammatory response. Studies to date are suggestive of clinical benefits from these approaches, especially in postsurgical patients.

Stimulation of allergen-loaded macrophages by TLR9-ligand potentiates IL-10-mediated suppression of allergic airway inflammation in mice

BACKGROUND

Previously, we demonstrated that OVA-loaded macrophages (OVA-Mphi) partially suppress OVA-induced airway manifestations of asthma in BALB/c mice. In vitro studies showed that OVA-Mphi start to produce IL-10 upon interaction with allergen-specific T cells, which might mediate their immunosuppressive effects. Herein, we examined whether IL-10 is essential for the immunosuppressive effects of OVA-Mphi in vivo, and whether ex vivo stimulation of the IL-10 production by OVA-Mphi could enhance these effects.

METHODS

Peritoneal Mphi were loaded with OVA and stimulated with LPS or immunostimulatory sequence oligodeoxynucleotide (ISS-ODN) in vitro. The increase of IL-10 production was examined and, subsequently, ex vivo stimulated OVA-Mphi were used to treat (i.v.) OVA-sensitized mice. To further explore whether Mphi-derived IL-10 mediates the immunosuppressive effects, Mphi isolated from IL-10-/- mice were used for treatment.

RESULTS

We found that stimulation with LPS or ISS-ODN highly increased the IL-10 production by OVA-Mphi (2.5-fold and 4.5-fold increase, respectively). ISS-ODN stimulation of OVA-Mphi significantly potentiated the suppressive effects on allergic airway inflammation. Compared to sham-treatment, ISS-ODN-stimulated OVA-Mphi suppressed the airway eosinophilia by 85% (vs. 30% by unstimulated OVA-Mphi), IL-5 levels in bronchoalveolar lavage fluid by 80% (vs. 50%) and serum OVA-specific IgE levels by 60% (vs. 30%). Importantly, IL-10-/-Mphi that were loaded with OVA and stimulated with ISS-ODN ex vivo, failed to suppress OVA-induced airway inflammation.

CONCLUSIONS

These results demonstrate that Mphi-derived IL-10 mediates anti-inflammatory responses in a mouse model of allergic asthma, which both can be potentiated by stimulation with ISS-ODN.

Gender affects macrophage cytokine and prostaglandin E2 production and PGE2 receptor expression after trauma1

BACKGROUND

Gender influences morbidity and mortality after injury. Hormonal differences are important; however, the role of prostaglandins as mediators in immune dysfunction relating to gender differences after trauma is unclear. We hypothesized that gender-dependent differences in PGE(2) receptor expression and signaling may be involved in immune-related differences. This study determined prostaglandin receptor subtype (EP1-EP4) expression following injury and determined whether gender differences influence EP receptor expression.

MATERIALS AND METHODS

BALB/c male and female mice (estrus and pro-estrus) (n = 6 per group) were subjected to femur fracture and 40% hemorrhage (trauma) or sham injury (anesthesia). Seven days later, the splenic macrophages were harvested and stimulated with lipopolysaccharide (Escherichia coli serotype O55:B5). After 6 h mRNA samples were collected for EP receptor mRNA expression and at 24 h supernatants were collected for PGE(2), TNF-alpha, and IL-6 production.

RESULTS

The expression of EP2-4 receptors was higher in female pro-estrus mice compared with male mice. EP1 receptor expression was higher in males than pro-estrus females. There was decreased expression of all four receptors after trauma in female estrus compared with control estrus mice. Macrophage PGE(2), TNF-alpha, and IL-6 production was significantly increased in injured female mice compared with female controls but there were no differences in injured male mice compared with male controls. PGE(2) and TNF-alpha production by traumatized male mice were significantly less than that produced by traumatized pro-estrus females.

CONCLUSIONS

These data suggest gender-related differences in response to traumatic injury and that alterations in specific EP receptor subtypes may be involved in immune dysfunction after injury. Studies to evaluate targeted modulation of these receptor subtypes may provide further insights to gender-specific differences in the immune response after injury.

Burn injury enhances brain prostaglandin E2 production through induction of cyclooxygenase-2 and microsomal prostaglandin E synthase in cerebral vascular endothelial cells in rats

OBJECTIVES

To examine whether peripheral burn injury in rats elevates prostaglandin E2 in the central nervous system and to determine where in the central nervous system enzymes responsible for prostaglandin E2 synthesis are expressed.

DESIGN

Prospective controlled animal study.

SETTING

University research laboratory.

SUBJECTS

Sprague-Dawley rats.

INTERVENTIONS

Rats received either approximately 25% full-thickness burn injury or sham treatment. At 36 hrs after the injury, the cerebrospinal fluid was sampled to measure prostaglandin E2, and the brain and the spinal cord were sampled for immunohistochemical detection of cyclooxygenase-2 and microsomal-type prostaglandin E2 synthase, enzymes that are responsible for prostaglandin E2 production.

MEASUREMENTS AND MAIN RESULTS

The prostaglandin E2 concentration in the cerebrospinal fluid was significantly elevated in the injured rats, and this elevation was suppressed by a cyclooxygenase-2-specific inhibitor, NS398. Only in the injured rats, cyclooxygenase-2 and microsomal-type prostaglandin E synthase proteins were detected in vascular endothelial cells throughout the central nervous system with no regional difference. A double-immunofluorescence study revealed that cyclooxygenase-2 and microsomal-type prostaglandin E synthase were coexpressed in the perinuclear region of the endothelial cells.

CONCLUSIONS

These results indicate that peripheral burn injury induces cyclooxygenase-2 and microsomal-type prostaglandin E synthase in endothelial cells of the central nervous system. These enzymes likely elevate the cerebrospinal fluid concentration of prostaglandin E2, a prostanoid that, in turn, activates prostaglandin E2 receptors on the central nervous system neurons involved in the general symptoms following burn injury.

High permeability haemofiltration improves peripheral blood mononuclear cell proliferation in septic patients with acute renal failure

BACKGROUND

Continuous veno-venous haemofiltration (HF) with high permeability (HP) haemofilters is a novel approach in the adjuvant therapy of septic patients. HP haemofilters are characterized by an increased pore size which facilitates the filtration of inflammatory mediators. The present study examines whether HP-HF has an impact on peripheral blood mononuclear cell (PBMC) proliferation and whether ultrafiltrate can alter PBMC function in isolates from healthy volunteers.

METHODS

Twenty-eight septic patients with acute renal failure were randomly allocated to either HP-HF or conventional HF (C-HF). HP-HF was performed with a newly developed high-flux polyamide membrane (P2SH) with a nominal cut-off point of 60 kDa. For C-HF, a high-flux polyamide haemofilter (Polyflux 11S; cut-off, 30 kDa) was used.

RESULTS

Septic patients demonstrated a significantly reduced proliferation of anti-CD3-stimulated PBMCs compared to healthy controls (P = 0.016). Initiating HF led to a restoration of the PBMC proliferation in HP-HF but not in C-HF. Exposing PBMCs isolated from healthy donors to ultrafiltrates from patients with sepsis demonstrated a significant suppressive effect of HP ultrafiltrates on the anti-CD3-stimulated PBMC proliferation (P = 0.011). Ultrafiltrate from patients with sepsis who received C-HF had no impact on PBMC proliferation.

CONCLUSION

HP-HF restores PBMC proliferation in septic patients probably by eliminating immunomodulatory mediators. HP-HF may represent a new renal replacement therapy able to modulate PBMC function in sepsis.

Influence of local anaesthetics on inflammatory activity postburn

Most studies investigating the pathophysiological processes taking place inside an experimental burn wound use in vitro techniques, which only allow for fragmented measurements of the actual and complex processes occurring inside a burn wound in vivo. In the present study, which used a recently developed in vivo technique in the rat, a full-thickness burn was induced and resulted in the formation of a subcutaneous gelatinous edema with distinct borders to the surrounding connective tissue and free communication with the systemic circulation allowing it to be easily separated for further analysis. In the present study, we investigated the effects of topical local anaesthetics (EMLA) on the inflammatory cascade of a burn wound in vivo. Results showed significantly higher myeloperoxidase (MPO) levels in EMLA-treated burned animals (P<0.01) versus placebo-treated burned controls. EMLA treatment induced a significant inhibition of the synthesis of leukotrien B(4) (LTB(4)) (P<0.001), prostaglandin E(1) (PGE(1)) (P<0.001), prostaglandin E(2) (PGE(2)) (P<0.001) and thromboxane B(2) (TXB(2)) (P<0.001) versus control, while free radical formation did not differ significantly between EMLA-treated and control animals. In conclusion, topical local anaesthetics significantly inhibit the release of several mediators known to take important part in the pathophysiological events ensuing a burn injury, such as activation of pain mechanisms (PGE), oedema formation (LTB), and postburn ischemia (TXB). The increased numbers of leukocytes (MPO) in the burn wound induced by topical local anaesthetic treatment could suggest increased influx and/or increased viability of leukocytes postburn.

Relationships between burn size, immunosuppression, and macrophage hyperactivity in a murine model of thermal injury

Burn injury induces immune dysfunction and alters numerous physiological parameters. While clinical studies indicate that burn injury size profoundly impacts patient immune status, only limited experimental studies have systematically addressed its impact on immune functional parameters. In the present study, mice were subjected to burn injuries of varying sizes and splenic immune cells (splenocytes and macrophages) were isolated 7 days thereafter. Burn injury suppressed splenic T-cell proliferation in an injury size-dependent manner that correlated with the release of the immunosuppressive mediators PGE(2) and nitric oxide. In addition, a shift towards an immunosuppressive Th-2 cytokine profile and a hyperactive macrophage phenotype (increased release of inflammatory mediators) was observed post-injury, however, this effect was in part independent of burn size. Thus, unlike patient survival data, burn injury-induced changes in immune function do not necessarily correlate with the size of the injury.

Macrophages and post-burn immune dysfunction

The activation of a pro-inflammatory cascade after burn injury appears to be important in the development of subsequent immune dysfunction, susceptibility to sepsis and multiple organ failure. Macrophages are major producers of pro-inflammatory mediators and their productive capacity for these mediators is markedly enhanced following thermal injury. Thus, macrophage hyperactivity (as defined by increased productive capacity for pro-inflammatory mediators) appears to be of critical importance in the development of post-burn immune dysfunction. This review will focus on the current state of knowledge with regards to the role of macrophages in the development of post-burn immune dysfunction. Particular areas of discussion include: nitric oxide synthase (NOS) and cyclooxygenase (COX) enzyme systems, macrophages and the T-helper (Th)-1/Th-2 cytokine responses, alterations in macrophages signal transduction and a potential role for gamma/delta T-cells in the development of macrophage hyperactivity following thermal injury. A more comprehensive understanding of the relationship between macrophage activity and post-burn immune dysfunction will hopefully provide the basis for improved therapeutic regimes in the treatment of burn patients.

N-3 polyunsaturated fatty acids and inflammation: from molecular biology to the clinic

The immune system is involved in host defense against infectious agents, tumor cells, and environmental insults. Inflammation is an important component of the early immunologic response. Inappropriate or dysfunctional immune responses underlie acute and chronic inflammatory diseases. The n-6 PUFA arachidonic acid (AA) is the precursor of prostaglandins, leukotrienes, and related compounds that have important roles in inflammation and in the regulation of immunity. Feeding fish oil results in partial replacement of AA in cell membranes by EPA. This leads to decreased production of AA-derived mediators, through several mechanisms, including decreased availability of AA, competition for cyclooxygenase (COX) and lipoxygenase (LOX) enzymes, and decreased expression of COX-2 and 5-LOX. This alone is a potentially beneficial anti-inflammatory effect of n-3 FA. However, n-3 FA have a number of other effects that might occur downstream of altered eicosanoid production or might be independent of this effect. For example, dietary fish oil results in suppressed production of proinflammatory cytokines and can modulate adhesion molecule expression. These effects occur at the level of altered gene expression. Fish oil feeding has been shown to ameliorate the symptoms of some animal models of autoimmune disease and to protect against the effects of endotoxin. Clinical studies have reported that oral fish oil supplementation has beneficial effects in rheumatoid arthritis and among some asthmatics, supporting the idea that the n-3 FA in fish oil are anti-inflammatory. There are indications that the inclusion of fish oil in enteral and parenteral formulae is beneficial to patients.

Dietary modification of inflammation with lipids

The n-3 polyunsaturated fatty acids (PUFA) eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are found in high proportions in oily fish and fish oils. The n-3 PUFA are structurally and functionally distinct from the n-6 PUFA. Typically, human inflammatory cells contain high proportions of the n-6 PUFA arachidonic acid and low proportions of n-3 PUFA. The significance of this difference is that arachidonic acid is the precursor of 2-series prostaglandins and 4-series leukotrienes, which are highly-active mediators of inflammation. Feeding fish oil results in partial replacement of arachidonic acid in inflammatory cell membranes by EPA. This change leads to decreased production of arachidonic acid-derived mediators. This response alone is a potentially beneficial anti-inflammatory effect of n-3 PUFA. However, n-3 PUFA have a number of other effects which might occur downstream of altered eicosanoid production or might be independent of this activity. For example, animal and human studies have shown that dietary fish oil results in suppressed production of pro-inflammatory cytokines and can decrease adhesion molecule expression. These effects occur at the level of altered gene expression. This action might come about through antagonism of the effects of arachidonic acid-derived mediators or through more direct actions on the intracellular signalling pathways which lead to activation of transcription factors such as nuclear factor kappa B (NFB). Recent studies have shown that n-3 PUFA can down regulate the activity of the nuclear transcription factor NFB. Fish oil feeding has been shown to ameliorate the symptoms in some animal models of chronic inflammatory disease and to protect against the effects of endotoxin and similar inflammatory challenges. Clinical studies have reported that oral fish oil supplementation has beneficial effects in rheumatoid arthritis and among some patients with asthma, supporting the idea that the n-3 PUFA in fish oil are anti-inflammatory. There are indications that inclusion of n-3 PUFA in enteral and parenteral formulas might be beneficial to patients in intensive care or post-surgery.

Alcohol, injury, and cellular immunity

It is widely accepted that alcohol exposure is a causative factor in the occurrence of burn or other traumatic injury. It is less well known that individuals who have consumed alcohol before sustaining an injury suffer from increased morbidity and mortality compared with the morbidity and mortality of non-alcohol-consuming subjects with similar injuries. Complications due to bacterial infection are the most common burn sequelae in injured patients and are frequently associated with depressed immunity. Independently, alcohol exposure and injury have been shown to influence cellular immunity negatively. These changes in immunity are closely linked to injury- or alcohol-induced alterations in the cytokine milieu in both clinical studies and animal models. Not surprisingly, the combination of insult of alcohol exposure and burn injury results in immune suppression that is greater in magnitude and duration compared with either insult alone. The combined effects of alcohol and injury on immunity have been examined in a limited number of studies. However, results of these studies support the suggestion that altered cytokine production is an integral part of the immune dysregulation and increased mortality that is observed. In particular, the increased presence of macrophage-derived mediators observed after burn or alcohol exposure alone seems to be synergistically increased in a combined injury model. Although more research is needed, it is likely that therapeutic modalities that include manipulation of cytokine networks to boost cellular immunity may improve outcome for patients who sustain injuries subsequent to consuming alcohol.

Alterations in lymphocyte function and relation to phospholipid composition after burn injury in humans

OBJECTIVE

Lymphocyte functions are dependent on fatty acid composition of membranes, and impaired functions can predispose patients to infection after burn injury. The current study was designed to describe changes in lymphocyte-phospholipid composition and lymphocyte-related immune functions from early to late recovery time points after burn injury.

DESIGN

Prospective observational.

SETTING

Firefighter's Burn Treatment Center, University of Alberta Hospital, Edmonton, Alberta, Canada.

PATIENTS

Subjects (n = 10) with >10% total body surface burn area.

MEASUREMENTS AND MAIN RESULTS

Blood was drawn from subjects at specific time points (0 days to >50 days) after burn injury. Fatty acid composition of the major phospholipid classes of isolated lymphocytes was determined by using gas liquid chromatography. Lymphocyte phenotypes and proliferation ([(3)H]-thymidine uptake and interleukin-2 and interferon-gamma production) in response to mitogens were determined. Lymphocyte phospholipid 20:4n-6 content was 30% to 60% lower early compared with late postburn time points (p <.001). Interferon-gamma production by stimulated cells was found to negatively correlate with n-3 content (r =.7, p =.008). The expression of CD25 on antigen-mature CD8+ cells was associated with higher proliferative responses (r =.88, p <.004). Proportion of CD8+ cells was lower, and the proportion of activated monocytes was higher early compared with late postburn (p <.05). Natural killer cell cytotoxicity was low early after burn and increased with recovery.

CONCLUSIONS

The results of this preliminary study suggest that immune activation occurs between the second and third week after burn injury, which is associated with changes in 20:4n-6 and n-3 fatty acid content of lymphocyte phospholipid. This study suggests that there is release or impaired synthesis of 20:4n-6 early after burn injury that may be related to functional changes in immune cells.

Appearance of monocyte chemoattractant protein 1 (MCP-1) early after thermal injury: role in the subsequent development of burn-associated type 2 T-cell responses

OBJECTIVE

To determine whether monocyte chemoattractant protein-1 (MCP-1), which initiates subsequent development of burn-associated type 2 T cells, is produced in mice early after thermal injury.

SUMMARY BACKGROUND DATA

A predominance of type 2 T-cell responses is commonly observed in animals and patients with severe thermal injuries. Burn-associated type 2 T cells have been identified as the cells responsible for the increased susceptibility of thermally injured mice to infections with herpes simplex virus type 1 and Candida albicans. Recently, the necessity of MCP-1 for the generation of type 2 T cells was shown in MCP-1 knockout mice. MCP-1 may have an important role in the increased susceptibility of thermally injured mice to various intracellular opportunistic pathogens.

METHODS

The production of MCP-1 in sera or in cultures of various cells prepared from thermally injured mice was measured. Dual-chamber transwell cultures were performed to determine the influence of MCP-1-producing cells on the generation of burn-associated type 2 T cells.

RESULTS

Without any stimulation, splenic macrophages from mice (1/2D-M(phi)) produced MCP-1 into their culture fluids 12 hours after thermal injury. Interleukin-4 was detected in culture fluids of splenic T cells from normal mice cultured with 1/2D-M(phi) in a dual-chamber transwell system; however, this cytokine was not produced by normal T cells cultured with normal macrophages in the transwells. Also, normal T cells cultured with 1/2D-M(phi) did not produce interleukin-4 when transwell cultures were performed in the presence of anti-MCP-1 monoclonal antibody. Further, normal T cells directly stimulated with MCP-1 produced interleukin-4 into their culture fluids. Normal T cells, cultured with 1/2D-M(phi) for 24 hours in the transwells and recultured with fresh medium for an additional 7 days, produced interleukin-10 (but not interferon-gamma) and expressed ST2L mRNA (but not interleukin-12 receptor beta2 chain) when they were stimulated with anti-CD3 monoclonal antibody.

CONCLUSIONS

Results indicate that MCP-1 is produced in mice within 1 day of thermal injury, and the subsequent development of burn-associated type 2 T-cell responses may be triggered by MCP-1 produced early after thermal injury.

Differential expression and tissue compartmentalization of the inflammatory response following thermal injury

Studies have shown that both animal tissue-fixed immune cells and human peripheral blood mononuclear cell (PBMC) functions are altered after burn injury. Additional studies suggest that the burn injury-induced alterations in these divergent cell populations from different species are similar. It remains unknown, however, whether the observed changes in animal tissue-fixed immune cell function following thermal injury also occurs to a similar extent in the PBMC population. The aim of our study was to compare PBMC and tissue-fixed immune cell functions from the same animal using a murine burn model. At 7 days post-burn, mice were more susceptible to sepsis and delayed type hypersensitivity responses were suppressed. Splenocytes isolated from injured mice displayed suppressed proliferation and increased IL-10 production. In contrast, PBMC from injured mice displayed suppressed proliferation, IL-2 and IFN-gamma production. Splenic macrophage nitric oxide, PGE(2), TNF-alpha, IL-6 and IL-10 production was enhanced post-burn and IL-12 production was suppressed. PBMC from such animals displayed enhanced PGE(2) production and suppressed IL-6 and IL-12 production. These results indicate that while an immunosuppressive Th(2) phenotype (increased IL-10 and/or suppressed IL-2, IFN-gamma) was induced in both the splenic and PBMC compartments post-injury, differential expression and dimorphism in the response also exists. Thus, the assessment of only PBMC function in burn patients may not accurately reflect the patient's actual immune status at the tissue level.

Cyclooxygenase 2-mediated suppression of macrophage interleukin-12 production after thermal injury

Macrophage (Mphi) prostaglandin (PG)E(2) production has been implicated in immunosuppression and increased susceptibility to sepsis after thermal injury. Deficient interleukin (IL)-12 production has also been implicated in these postburn complications. The present study examined the relationship between Mphi cyclooxygenase (COX)-2 activity and IL-12 production after thermal injury. C57BL/6 female mice were subjected to a 25% total body surface area full-thickness burn. Mphi were isolated 7 days later, or the mice were subjected to sepsis by cecal ligation and puncture (CLP). IL-12 production by Mphi from injured mice was suppressed by >50%, whereas COX-2 expression and PGE(2) production were increased twofold. The COX-2 inhibitor NS-398 suppressed PGE(2) production and normalized IL-12 production in the injury group, whereas it had no effect on IL-10 production. Injured mice subjected to CLP had lower IL-12 plasma levels compared with sham-treated mice subjected to CLP. NS-398 treatment prevented the suppression in plasma IL-12 levels in the injury group. Thus elevated Mphi COX-2 activity, independent of IL-10, suppresses Mphi IL-12 production after thermal injury and may play an important role in the observed immunosuppression under such conditions.

Prostaglandin E2 receptors EP2 and EP4 are down-regulated in human mononuclear cells after injury

BACKGROUND

Recent characterization of prostaglandin receptor subtypes shows that each is critical to cellular functions and operates through separate signaling pathways that may explain differing effects of prostanoids. This study aimed to determine whether prostaglandin receptors EP2 and EP4 are modulated after injury and to evaluate the effect of prostaglandin E(2) (PGE(2)) addition and blockade on EP receptor expression.

METHODS

Peripheral blood mononuclear cells (PBMCs) isolated from 10 patients sustaining fracture or burn injury and 10 control subjects were stimulated with lipopolysaccharide +/- NS-398, an inhibitor of PGE(2) production. Samples were evaluated for production of PGE(2), tumor necrosis factor--alpha, and leukotriene B(4) as well as mRNA expression of EP receptors and COX-2. EP receptor expression was also evaluated after treating control PBMCs with PGE(2).

RESULTS

PBMCs from injured patients exhibited significant increases in PGE(2) production and COX-2 mRNA compared with control subjects, and these increases were inhibited by NS-398. In contrast, EP2 and EP4 receptors were markedly down-regulated after injury and NS-398 restored expression to control levels. Decreased EP2 and EP4 receptor expression after injury was replicated by coincubation of PBMCs with PGE(2).

CONCLUSIONS

Specific PGE(2) receptors are down-regulated after injury and NS-398 reverses this response. Furthermore, PGE(2) mediates EP2 and EP4 down-regulation. These data suggest that specific EP receptor subtypes may provide critical targets for augmenting the immune response after injury in humans.

Fatty acid content of plasma lipids and erythrocyte phospholipids are altered following burn injury

The objective of this study was to examine compositional and quantitative changes in fatty acids of plasma components and red blood cell phospholipids (PL) immediately following and during recovery from burn injury. Subjects (n = 10) with >10% total body surface area burn had blood drawn at specific timepoints (0 to >50 d) following burn injury. Fatty acid composition of red blood cell PL and plasma PL, cholesteryl esters (CE), and triglycerides was determined using gas-liquid chromatography after separating each fraction from extracted lipids by thin-layer chromatography. Total plasma PL and CE in burn patients were lower than in healthy control subjects with reduced 20:4n-6, n-6, and n-3 fatty acids and higher levels of monounsaturated and saturated fatty acids early after burn. CE levels remained half that of healthy control values up to 50 d post-burn. Red blood cell PL had decreased 20:4n-6 content and profiles similar to that of an essential fatty acid deficiency early after burn. These results suggest an impairment in lipoprotein and polyunsaturated fatty acid metabolism in the early post-burn period. Lower levels of 20:4n-6 and n-3 fatty acids in every plasma fraction suggest increased use of these fatty acids for wound healing and immune function following burn injury. Further work is needed to determine the ability of burn patients to utilize essential fatty acids in order to design nutritional intervention that promotes wound healing and immunological functions consistent with recovery in these patients.

NS-398 Treatment after Trauma Modifies NF-κB Activation and Improves Survival

Prostaglandin E(2) (PGE(2)) production after trauma contributes to immune alterations that increase susceptibility to infections. We hypothesize that blocking PGE(2) with NS-398, a selective COX-2 inhibitor, will modulate this response and improve outcome. This study evaluated the effect of NS-398 given over 7 days on proinflammatory cytokines, intracellular signaling, and survival after a septic challenge. Balb/C mice (n = 8/group) were given 10 mg/kg NS-398 intraperitoneally over 7 days, starting after anesthesia or trauma (femur fracture + 40% hemorrhage). Four groups, anesthesia + vehicle (C), anesthesia + NS-398 (CN), trauma + vehicle (T), or trauma + NS-398 (TN), were studied. On Day 7 after trauma, mice were sacrificed, serum was collected, and splenic macrophages were evaluated for PGE(2), LTB(4), IL-6, TNF-alpha, and NO production. Additionally, macrophage COX-2 mRNA, IkappaB-alpha, and NF-kappaB were evaluated. In a separate study, mice (n = 10-11/group) were traumatized and given NS-398 over 7 days, and then cecal ligation and puncture (CLP) were performed. Mice were then followed for survival over 10 days (via log-rank test). NS-398 treatment of injured mice decreased PGE(2) production compared to T (3.9 +/- 0.3 vs 3.1 +/- 0.4 pg/microg protein), and significantly decreased IL-6, NO, and TNF-alpha production. NS-398 treatment also attenuated COX-2 mRNA levels and NF-kappaB activation. These cellular events correlate with a significant survival advantage in TN versus T mice after CLP. These data suggest that a specific COX-2 inhibitor not only suppresses PGE(2), but normalizes proinflammatory cytokines after trauma through changes that may partly be mediated via transcriptional events. This correlates with significantly increased survival in TN mice given a septic challenge and suggests that COX-2 inhibitors contribute to modulating the inflammatory response and improving survival after trauma.

Glycyrrhizin restores the impaired IL-12 production in thermally injured mice

Mice 6 days after thermal injury (TI-mice) did not respond to lipopolysaccharide (LPS) stimulation for production of serum interleukin 12 (IL-12; 2 h after LPS stimulation, <20 pg/ml in TI-mice; 1091+/-162 pg/ml in normal mice). However, 2 h after LPS stimulation, 1456+/-118 pg/ml of IL-12 were demonstrated in sera of TI-mice previously treated with a 10 mg/kg i.p. dose of glycyrrhizin (GR). IL-12 was not induced by LPS in sera of normal mice inoculated with burn-associated type 2 T cells (IL-4/IL-10-producing CD8+CD11b+TCRgamma/delta+T cells isolated from spleens of TI-mice). However, IL-12 production was induced by LPS in sera of these mice previously treated with GR or a mixture of monoclonal antibodies (mAbs) for type 2 cytokines. Also, IL-12 production was induced by LPS in TI-mice inoculated with CD4+T cells from spleens of GR-treated normal mice (GR-CD4+T cells, 5x10(6)cells/mouse). Since GR-CD4+T cells have been shown to be antagonistic cells against production of type 2 cytokines by burn-associated type 2 T cells, these results indicate that IL-12 unresponsiveness shown in TI-mice is recovered by GR through the regulation of burn-associated type 2 T cell responses.

Human alveolar macrophages induce functional inactivation in antigen-specific CD4 T cells

BACKGROUND

Alveolar macrophages (AMCs) are the most abundant phagocytic cells in the lung, but they present antigen poorly to T cells.

OBJECTIVES

The objectives of our studies were to more clearly define the mechanisms by which AMCs present antigen to T cells and to determine whether AMCs actively inhibit T-cell activation.

METHODS

We studied purified human CD4 T cells and compared the capacity of allogeneic AMCs and peripheral blood monocytes to induce T-cell proliferation and cytokine production.

RESULTS

We previously demonstrated that human AMCs fail to upregulate expression of B7-1 and B7-2 on stimulation with IFN-gamma. We now demonstrate that AMCs actively induce T-cell unresponsiveness (functional inactivation) in an antigen-specific manner and reduce the capacity of CD4 T cells to respond on secondary stimulation. The induction of unresponsiveness was reversed by the addition of CD28 costimulation or IL-2. However, interruption of Fas/Fas ligand interactions or of B7/CTLA-4 interactions did not prevent unresponsiveness, indicating that neither CTLA-4 triggering nor Fas-induced apoptosis was involved in the induction of T-cell unresponsiveness.

CONCLUSIONS

These studies indicate that AMCs actively tolerize CD4 T cells in an antigen-specific fashion. We propose that AMCs mediate a form of immune privilege in the lungs that effectively limits immune responses in the pulmonary compartment but has little effect on systemic immunity.

Parenteral supplementation with a fish-oil emulsion prolongs survival and improves rat lymphocyte function during sepsis

Nutritional intervention with omega-3 fatty acids during trauma and infection has been shown to improve the clinical outcome of patients and the survival rate in laboratory animals. This study evaluated the effects of parenteral administration of lipid emulsions containing fish oil (FO) or soybean oil (SBO) on survival and T-lymphocyte response during sepsis. Male Sprague-Dawley rats (250-275 g) were prepared for parenteral feeding 4 d before inducing sepsis by cecal ligation and puncture (CLP). Standard resuscitation was provided with normal saline. Thirty minutes after completing CLP, sham control or CLP rats were infused continuously with saline or a parenteral diet containing SBO or a 1:1 FO:SBO emulsion. The survival rate was significantly improved in rats receiving the FO-supplemented diet, with 50% alive by 120 h in comparison with the saline-infused, chow-fed rats (0% alive by 120 h) or the SBO-fed rats (12% alive at 120 h). The T-lymphocyte response was evaluated at 24 h after CLP. Sepsis led to a decline in lymphocyte proliferation in rats infused with saline or the SBO emulsion, which was associated with a greater release of splenocyte interleukin-10, transforming growth factor-beta and prostaglandin E2. Administering the 1:1 FO:SBO parenteral diet during sepsis improved the survival rate and prevented the sepsis-induced suppression of lymphocyte proliferation and interleukin-2 release. The FO effect on lymphocyte function was associated with decreased splenocyte release of transforming growth factor-beta and prostaglandin E2.

PGE2 suppresses mitogen-induced Ca2+ mobilization in T cells

PGE2-mediated suppression of T cell proliferation during sepsis could result from altered Ca2+ signaling. The present study evaluated the effects of PGE2 on Ca2+ release from intracellular stores and its influx through the plasma membrane in splenic T cells from Sprague-Dawley rats. Intracellular Ca2+ concentration ([Ca2+]i) responses in individual T cells were assessed using the Ca2+ imaging technique, and the release of Ca2+ from intracellular stores and Ca2+ influx were spectrofluorometrically quantified in T cell suspensions. Under unstimulated conditions, nearly 85% of T cells exhibited [Ca2+]i </=50 nM. After stimulation with concanavalin A (Con A), an increase in [Ca2+]i was recorded in approximately 60% of the cells. The pretreatment of T cells with PGE2 had no apparent effect on [Ca2+]i in resting cells; it significantly suppressed the Con A-induced increase in [Ca2+]i in all of the Con A-responsive cells. Ca2+ release from the intracellular stores contributed to the early spike in [Ca2+]i, and the late phase of elevation in [Ca2+]i was dependent on Ca2+ influx through the plasma membrane. Our data suggest that PGE(2) causes an overall suppression of the Con A-induced [Ca2+]i elevation in T cells via inhibiting both Ca2+ influx and its release from the intracellular stores.

Role of protein kinase C in cyclic AMP-mediated suppression of T-lymphocyte activation following burn injury

Major burn injury induces T-lymphocyte dysfunction. Previous studies suggest that prostaglandin (PG) E2, which is elevated post-burn, is the causative factor via a cyclic AMP-dependent process. The present study was conducted to elucidate the mechanism by which cAMP induces T-lymphocyte dysfunction following burn injury. Splenocytes were isolated from mice 7 days after receiving a scald burn covering 25% of their total body surface or sham procedure. ConA-induced proliferation by splenocytes from burned mice was significantly suppressed. Macrophage depletion of the splenocyte cultures abrogated the suppression. Concanavalin A-stimulated proliferation by macrophage-depleted splenocytes was suppressed by PGE2 and dibutyryl cAMP in both groups. The IC50 of these cAMP-elevating agents, however, was approximately 100-fold lower for cells from burned mice, indicating an increased sensitivity to cAMP. PGE2 did not suppress PMA/Ca2+ ionophore-induced T-lymphocyte activation. Addition of PMA to ConA-stimulated cultures prevented the suppression of proliferative responses by PGE2, whereas Ca2+ ionophore had no effect. Thus, the suppression of T-lymphocyte activation following burn injury is macrophage-dependent, related to an increased sensitivity to cAMP and due to an uncoupling of cell surface receptors from protein kinase C activation.

Gadolinium chloride inhibits lipopolysaccharide-induced mortality and in vivo prostaglandin E2 release By splenic macrophages

The monocytic phagocytic system, consisting primarily of tissue macrophages of the liver and spleen, produces prostaglandin E(2) (PGE(2)), a modulator of the septic response. Macrophages are known to internalize gadolinium chloride (GD), a lanthanide metal, which inhibits phagocytic function. Thus we studied the effect of in vivo GD on lipopolysacchride (LPS)-induced mortality and on LPS-stimulated PGE(2) release by cultured splenic macrophages. GD (7 mg/kg intravenously) given on the two days prior to LPS challenge (30 mg/kg intravenously) completely prevented the uniform mortality in rats. This protective effect was transient since rechallenge with LPS 10 days later was uniformly lethal. Previous work in this laboratory has established a critical role of arginine concentration on macrophage behavior in vitro. Therefore, to establish culture conditions reflective of the milieu within the portal venous system, alanine and arginine levels were measured in the portal and hepatic veins of normal and endotoxemic (LPS, 10 mg/kg intraperitoneally) rats. In contrast to alanine levels, which were not altered by endotoxemia, there was a reduction of arginine concentrations from a range of 50 to 250 micromol/L in normal rats to a range of 10 to 50 micromol/L after LPS challenge. Consequently subsequent in vitro assays of splenic macrophage secretory behavior were performed in concentrations of 1200 micromol/L arginine (in standard RPMI-1640), as well as in concentrations reflective of physiologic arginine levels (10 and 100 micromol/L in modified RPMI-1640). Rat splenic macrophages harvested after two consecutive days of either in vivo saline or GD injection (7 mg/kg intravenously) were stimulated with LPS (0.025 to 2.5 microg/ml). At 72 hours of culture, the release of PGE(2) by splenic macrophages from GD-treated rats was significantly (P <0.0001) reduced at all LPS concentrations. Increased PGE(2) production was not present when the splenic macrophages were cultured in the supraphysiologic arginine (1200 micromol/L) concentration. The results demonstrate the relevance of physiologic arginine concentrations in cell culture studies and suggest that the protection conferred by GD against septic mortality may be related to downregulation of the release of immunosuppressive PGE(2) by the monocytic phagocytic system.

Gadolinium blocks rat Kupffer cell calcium channels: relevance to calcium-dependent prostaglandin E2 synthesis and septic mortality

Hepatic Kupffer cells (KC), the major tissue macrophage population, produce the septic response mediators, tumor necrosis factor alpha (TNF-alpha) and prostaglandin E2 (PGE2), and have been shown to internalize gadolinium chloride (GD), a rare earth metal of the lanthanide series. Because GD pretreatment of rats has been shown to inhibit the mortality of sepsis, we studied the secretory response to lipopolysaccharide (LPS) by KC isolated from rats injected with either saline or GD (7 mg/kg, intravenously) on the 2 days before KC isolation. Using culture conditions modified to reflect the intrasinusoidal milieu of arginine (RPMI-1640 media with 10 or 100 micromol/L arginine), KC from GD-treated rats responded to LPS (0. 0025 microg/mL) with significantly (P <.01) reduced PGE2 release. In contrast, TNF-alpha release by treated KC was significantly (P <.05) enhanced, consistent with the loss of PGE2 autocoid inhibition of TNF-alpha. Calcium flux is an early signaling event in eicosanoid synthesis, and GD is known to block calcium channels. Therefore, KC were loaded with fura-2-AM to study the effect of GD on KC calcium flux. GD prevented ionomycin and platelet-activating factor (PAF)-mediated [Ca++]i increase and calcium-dependent PGE2 synthesis, while GD did not affect PGE2 synthesis when protein kinase C (PKC) was directly activated with tetradecanoylphorbolacetate (TPA). The inhibition of calcium flux and calcium-dependent PGE2 synthesis in the major cell of the monocytic phagocytic system by GD may explain the previously reported ability of this lanthanide to prevent the mortality of endotoxemia.

Pharmacological nutrition after burn injury

Burn patients develop pathophysiological alterations, which include extensive nitrogen loss, malnutrition, markedly increased metabolic rate and immunologic deficiency. This predisposes burn patients to frequent infections, poor wound healing, increased length of hospitalization and increased mortality. The nutritional support requires high protein and high energy diets preferably administered enterally soon after injury. The effects of increased dietary components such as glutamine, arginine and (n-3) fatty acids and related compounds have been evaluated in burn victims. These components, when supplied in quantities two to seven times of those in normal diets of healthy persons, appear to have beneficial pharmacological effects on the pathophysiological alterations associated with burns. However, the efficacy of immune-enhancing diets remains to be convincingly shown.

Lymphocyte function in wound healing and following injury

BACKGROUND

Injury activates a cascade of local and systemic immune responses.

METHODS

A literature review was undertaken of lymphocyte function in wound healing and following injury.

RESULTS

Lymphocytes are not required for the initiation of wound healing, but an intact cellular immune response is essential for a normal outcome of tissue repair. Injury affects lymphocyte immune mechanisms leading to generalized immunosuppression which, in turn, increases host susceptibility to infection and sepsis. Although the exact origin of post-traumatic immunosuppression remains unknown, stress hormones and immunosuppressive factors, such as inflammatory cytokines, prostaglandin E2 and nitric oxide, affect lymphocyte function adversely. Post-traumatic impairment of T lymphocyte immune function is reflected in decreased lymphocyte numbers, as well as altered T cell phenotype and activity. Antibody-producing B lymphocytes are variably affected by injury, probably secondary to alterations of T lymphocyte function, as a result of their close interaction with helper T cells. Therapeutic modulation of the host immune response may include non-specific and specific interventions to improve overall defence mechanisms.

CONCLUSION

Early resuscitation to restore lymphocyte function after injury is important for tissue repair and the prevention of immunosuppression.