An increase in the susceptibility of burned patients to infectious complications due to impaired production of macrophage inflammatory protein 1 alpha

Activating macrophages for enhanced osteogenic and bactericidal performance by Cu ion release from micro/nano-topographical coating on a titanium substrate

In the field of orthopaedics, inflammation-modulatory biomaterials are receiving increasing attentions due to their abilities to regulate innate immune response and mediate wound healing. In the current work, a Cu-containing micro/nano-topographical bio-ceramic surface (Cu-Hier-Ti surface) was employed as material model to explore the role played by Cu²⁺ release or material surface in regulating macrophage polarization as well as macrophage-mediated osteogenic and bactericidal effect. A Cu-free micro-topographical surface (Micro-Ti surface) generated by micro-arc oxidation was employed as control. The results showed that Cu²⁺ supplemented directly into the culture medium or released from Cu-Hier-Ti surface could polarize macrophages to pro-inflammatory M1 phenotype by activating Cu-transport signaling (copper transporter 1 (CTR1) and ATP7A) in macrophages, while the material characteristics exhibited anti-inflammatory effect to some extent by regulating integrin (α5, αM, β1 and β2) and TLR (TLR-3, TLR-4, Myd88 and Ticam-1/2) signaling. Macrophages grown on Cu-Hier-Ti surface or treated by Cu²⁺ could create a favorable inflammatory microenvironment for osteoblast-like SaOS-2 cell proliferation and differentiation. Moreover, Cu-Hier-Ti surface promoted macrophage capacity to engulf and kill bacteria, even though it did not show direct bactericidal effect against Staphylococcus aureus. In vivo results showed that Cu-Hier-Ti surface could lead to promoted osteointegraion and enhanced expression levels of M1 surface marker CD11c, growth factor BMP-6 and osteogenic makers including osteocalcin (OCN) and Runx-2 at the biomaterial/bone tissue interface in a rat model. The results indicate that Cu could be employed as a promising inflammation-modulatory agent to activate macrophages for enhanced osteogenic and bactericidal effect. STATEMENT OF SIGNIFICANCE: The next generation of bone biomaterials should be active to regulate the local inflammatory environment such that it favors bone regeneration. For the design and development of Cu-containing inflammation-modulatory biomaterials, it is of great importance to recognize the exact role played by Cu²⁺ release or material surface characteristics. So far, relatively little is known about the regulatory role of Cu²⁺ or micro/nano-topographical surface on macrophages. The results in the current work suggest that Cu²⁺ release and material surface characteristics of Cu-containing micro/nano-topographical coating could activate distinct signaling pathways in macrophages. The activated M1 macrophages exhibited stimulatory effect on osteoblast maturation and enhanced bactericidal capacity against Staphylococcus aureus. This study might provide new thoughts for the development of multi-functional Cu-containing biomaterials.

Trauma-Induced Nanohydroxyapatite Deposition in Skeletal Muscle is Sufficient to Drive Heterotopic Ossification

Heterotopic ossification (HO), or the pathologic formation of bone within soft tissues, is a significant complication following severe injuries as it impairs joint motion and function leading to loss of the ability to perform activities of daily living and pain. While soft tissue injury is a prerequisite of developing HO, the exact molecular pathology leading to trauma-induced HO remains unknown. Through prior investigations aimed at identifying the causative factors of HO, it has been suggested that additional predisposing factors that favor ossification within the injured soft tissues environment are required. Considering that chondrocytes and osteoblasts initiate physiologic bone formation by depositing nanohydroxyapatite crystal into their extracellular environment, we investigated the hypothesis that deposition of nanohydroxyapatite within damaged skeletal muscle is likewise sufficient to predispose skeletal muscle to HO. Using a murine model genetically predisposed to nanohydroxyapatite deposition (ABCC6-deficient mice), we observed that following a focal muscle injury, nanohydroxyapatite was robustly deposited in a gene-dependent manner, yet resolved via macrophage-mediated regression over 28 days post injury. However, if macrophage-mediated regression was inhibited, we observed persistent nanohydroxyapatite that was sufficient to drive the formation of HO in 4/5 mice examined. Together, these results revealed a new paradigm by suggesting the persistent nanohydroxyapatite, referred to clinically as dystrophic calcification, and HO may be stages of a pathologic continuum, and not discrete events. As such, if confirmed clinically, these findings support the use of early therapeutic interventions aimed at preventing nanohydroxyapatite as a strategy to evade HO formation.

Risk of pneumonia in patients with burn injury: a population-based cohort study

Background

Burns are the main cause of accidental injury, and pneumonia is a common respiratory disease in humans.

Aim

The purpose of this study was to investigate the relationship between burn injury and pneumonia.

Patients and methods

A nationwide population-based cohort study was conducted using data from the National Health Insurance Research Database in Taiwan. We identified and enrolled 2,893 subjects with burn injury, who were individually matched to 2,893 subjects in the comparison group by using the propensity score. Furthermore, we used a self-controlled case-series design to estimate the temporal association between burn injury and pneumonia.

Results

Exposure to burn injury revealed a higher risk of pneumonia than that to non-burn injury within 1 year. The Cox proportional hazards model revealed that, compared with the non-burn injury, burn injury yielded a 2.39-fold (95% CI=1.44-3.96) increase in risk of pneumonia. The exposure period of burn injury within 30 days showed 2.76-fold increase in risk of pneumonia (95% CI=1.44-3.96) compared with that in the baseline period.

Conclusion

Burn injury was associated with a significant increased risk of pneumonia, especially occurring within 30 days.

The Polarization of M2b Monocytes in Cultures of Burn Patient Peripheral CD14+ Cells Treated with a Selected Human CCL1 Antisense Oligodeoxynucleotide

M2b macrophages (Mφ) play a major role in the increased susceptibility of subacutely burned patients, to sepsis stemming from enterococcal translocation. Certain opportunistic infections in severely burned mice have been controlled by murine CCL1 antisense oligodeoxynucleotide (ODN), a specific polarizer of mouse M2bMφ. In the present study, we have screened CCL1 antisense ODN, which is active against human M2bMφ. Among the 20 CCL1 antisense ODNs synthesized in our laboratory, HCA-11 was shown to be the most active polarizer for human CCL1⁺CD163⁺CD14⁺ cells. Burn patient CCL1⁺CD163⁺CD14⁺ cells (3 × 10⁵ cells/mL) switched to quiescent CCL1^-CD163^-CD14⁺ cells within 48 h in cultures supplemented with 100 μg/mL of HCA-11. After treatment with a 25 μg/chimera dose of HCA-11, the bacterial growth was not observed in various organs of patient chimeras (γNSG mice inoculated with burn patient WBCs) infected with a lethal dose of Methicillin-resistant Staphylococcus aureus. The host antibacterial defenses against certain opportunistic pathogens should be improved in severely burned patients treated with a human CCL1 antisense ODN, HCA-11.

Biomarker-based classification of bacterial and fungal whole-blood infections in a genome-wide expression study

Sepsis is a clinical syndrome that can be caused by bacteria or fungi. Early knowledge on the nature of the causative agent is a prerequisite for targeted anti-microbial therapy. Besides currently used detection methods like blood culture and PCR-based assays, the analysis of the transcriptional response of the host to infecting organisms holds great promise. In this study, we aim to examine the transcriptional footprint of infections caused by the bacterial pathogens Staphylococcus aureus and Escherichia coli and the fungal pathogens Candida albicans and Aspergillus fumigatus in a human whole-blood model. Moreover, we use the expression information to build a random forest classifier to classify if a sample contains a bacterial, fungal, or mock-infection. After normalizing the transcription intensities using stably expressed reference genes, we filtered the gene set for biomarkers of bacterial or fungal blood infections. This selection is based on differential expression and an additional gene relevance measure. In this way, we identified 38 biomarker genes, including IL6, SOCS3, and IRG1 which were already associated to sepsis by other studies. Using these genes, we trained the classifier and assessed its performance. It yielded a 96% accuracy (sensitivities >93%, specificities >97%) for a 10-fold stratified cross-validation and a 92% accuracy (sensitivities and specificities >83%) for an additional test dataset comprising Cryptococcus neoformans infections. Furthermore, the classifier is robust to Gaussian noise, indicating correct class predictions on datasets of new species. In conclusion, this genome-wide approach demonstrates an effective feature selection process in combination with the construction of a well-performing classification model. Further analyses of genes with pathogen-dependent expression patterns can provide insights into the systemic host responses, which may lead to new anti-microbial therapeutic advances.

The pediatric sepsis biomarker risk model: potential implications for sepsis therapy and biology

Sepsis remains a major cause of morbidity and mortality in adult and pediatric intensive care units. Heterogeneity of demographics, comorbidities, biological mechanisms, and severity of illness leads to difficulty in determining which patients are at highest risk of mortality. Determining mortality risk is important for weighing the potential benefits of more aggressive interventions and for deciding whom to enroll in clinical trials. Biomarkers can be used to parse patients into different risk categories and can outperform current methods of patient risk stratification based on physiologic parameters. Here we review the Pediatric Sepsis Biomarker Risk Model that has also been modified and applied to estimate mortality risk in adult patients. We compare the two models and speculate on the biological implications of the biomarkers in patients with sepsis.

M2b monocytes predominated in peripheral blood of severely burned patients

Severely burned patients were shown to be carriers of M2 monocytes, and all of the monocytes isolated from peripheral blood of severely burned patients (19 of 19 patients) were demonstrated as M2b monocytes (IL-12(-)IL-10(+)CCL1(+) monocytes). Low levels of M2a (IL-12(-)IL-10(+)CCL17(+) monocytes) and M2c monocytes (IL-12(-)IL-10(+)CXCL13(+) monocytes) were demonstrated in peripheral blood of severely burned patients (M2a, 2 of 19 patients; M2c, 5 of 19 patients). M2b, M2a, and M2c monocytes were not detected in peripheral blood of healthy donors. However, M2b monocytes appeared when healthy donor monocytes were cultured in media supplemented with burn patient serum (15%). CCL2 was detected in sera of all burn patients, and M2b monocytes were not generated from healthy donor monocytes cultured with media containing 15% burn patient sera that were previously treated with anti-CCL2 mAb. In addition, M2b monocytes were generated from healthy donor monocytes in cultures supplemented with rCCL2. These results indicate that M2b monocytes are predominant in peripheral blood of severely burned patients who are carriers of CCL2 that functions to stimulate monocyte conversion from resident monocytes to M2b monocytes.

Polymerization of MIP-1 chemokine (CCL3 and CCL4) and clearance of MIP-1 by insulin-degrading enzyme

Macrophage inflammatory protein-1 (MIP-1), MIP-1α (CCL3) and MIP-1β (CCL4) are chemokines crucial for immune responses towards infection and inflammation. Both MIP-1α and MIP-1β form high-molecular-weight aggregates. Our crystal structures reveal that MIP-1 aggregation is a polymerization process and human MIP-1α and MIP-1β form rod-shaped, double-helical polymers. Biophysical analyses and mathematical modelling show that MIP-1 reversibly forms a polydisperse distribution of rod-shaped polymers in solution. Polymerization buries receptor-binding sites of MIP-1α, thus depolymerization mutations enhance MIP-1α to arrest monocytes onto activated human endothelium. However, same depolymerization mutations render MIP-1α ineffective in mouse peritoneal cell recruitment. Mathematical modelling reveals that, for a long-range chemotaxis of MIP-1, polymerization could protect MIP-1 from proteases that selectively degrade monomeric MIP-1. Insulin-degrading enzyme (IDE) is identified as such a protease and decreased expression of IDE leads to elevated MIP-1 levels in microglial cells. Our structural and proteomic studies offer a molecular basis for selective degradation of MIP-1. The regulated MIP-1 polymerization and selective inactivation of MIP-1 monomers by IDE could aid in controlling the MIP-1 chemotactic gradient for immune surveillance.

Role of natural killer dendritic cells in host resistance against Pseudomonas aeruginosa infection after thermal injury in mice

The contributions of dendritic cells (DCs) and natural killer dendritic cells (NKDCs) on host antibacterial innate immunities have been described. We have previously reported that mice with partial-thickness burn injuries (PT-burn mice) are resistant to burn wound infections, whereas mice with full-thickness burn injuries (FT-burn mice) are susceptible. In this study, the effect of burn stress on the appearance and properties of DCs and NKDCs was investigated in two different murine models of thermal injury. Dendritic cells isolated from PT-burn mice produced CCL3 and IL-12, whereas these soluble factors were not produced by DCs from FT-burn mice. As compared with unburned mouse controls, a large number of NKDCs were isolated from the DC preparations from PT-burn mice, whereas fewer NKDCs were detected in the DC preparations from FT-burn mice. Nonobese diabetic severe combined immunodeficiency mice inoculated with NKDCs were shown to be resistant against a lethal s.c. Pseudomonas aeruginosa infection. These results strongly suggest that NKDCs influenced by partial-thickness burn injury play a role on the resistance of PT-burn mice to P. aeruginosa s.c. infection.

The post sepsis-induced expansion and enhanced function of regulatory T cells create an environment to potentiate tumor growth

One of the more insidious outcomes of patients who survive severe sepsis is profound immunosuppression. In this study, we addressed the hypothesis that post septic immune defects were due, in part, to the presence and/or expansion of regulatory T cells (Tregs). After recovery from severe sepsis, mice exhibited significantly higher numbers of Tregs, which exerted greater in vitro suppressive activity compared with controls. The expansion of Tregs was not limited to CD25(+) cells, because Foxp3 expression was also detected in CD25(-) cells from post septic mice. This latter group exhibited a significant increase of chromatin remodeling at the Foxp3 promoter, because a marked increase in acetylation at H3K9 was associated with an increase in Foxp3 transcription. Post septic splenic dendritic cells promoted Treg conversion in vitro. Using a solid tumor model to explore the function of Tregs in an in vivo setting, we found post septic mice showed an increase in tumor growth compared with sham-treated mice with a syngeneic tumor model. This observation could mechanistically be related to the ability of post septic Tregs to impair the antitumor response mediated by CD8(+) T cells. Together, these data show that the post septic immune system obstructs tumor immunosurveillance, in part, by augmented Treg expansion and function.

[Dendritic cells in sepsis: an approach to post-infectious immunosuppression]

Dendritic cells (DCs) play a decisive role in the immune system, especially in the initial events that determine coordination between the innate and adaptive response. Moreover, they are antigen-presenting cells which, through contact with T cells, determine the type of immune responses towards inflammatory or anti-inflammatory. Currently, the hypothesis that attributes importance to the development of a post-infectious immunosuppression in the prognosis of the septic patient is growing stronger. It has been possible to verify the role played by these cells in this type of immunosuppression by the significant decrease in the number of DCs and by the dysfunctions in the functional capacity that include, on the one hand, the abnormal cytokine production and, on the other hand, the alterations in communication between the DCs and T cells that constitute an essential immunological fact. Further research into the knowledge regarding the DCs, in the context of severe infection, may help to consolidate some encouraging data that indicate these cells as: 1) an effective tool for monitoring the acute infection, 2) a discriminatory variable that may help determine the risk of nosocomial infection and 3) in a longer term, a treatment target that would restore the immunological abnormalities that occur in sepsis.

The hepatic response to thermal injury: is the liver important for postburn outcomes?

Thermal injury produces a profound hypermetabolic and hypercatabolic stress response characterized by increased endogenous glucose production via gluconeogenesis and glycogenolysis, lipolysis, and proteolysis. The liver is the central body organ involved in these metabolic responses. It is suggested that the liver, with its metabolic, inflammatory, immune, and acute phase functions, plays a pivotal role in patient survival and recovery by modulating multiple pathways following thermal injury. Studies have evaluated the role and function of the liver during the postburn response and showed that liver integrity and function are essential for survival, and that hepatic acute phase proteins are strong predictors for postburn survival. This review discusses these studies and delineates the pivotal role of the liver in patients following severe thermal injury.

The role of MIP-1 alpha in the development of systemic inflammatory response and organ injury following trauma hemorrhage

Although MIP-1alpha is an important chemokine in the recruitment of inflammatory cells, it remains unknown whether MIP-1alpha plays any role in the development of systemic inflammatory response following trauma-hemorrhage (T-H). C57BL/6J wild type (WT) and MIP-1alpha-deficient (KO) mice were used either as control, subjected to sham operation (cannulation or laparotomy only or cannulation plus laparotomy) or T-H (midline laparotomy, mean blood pressure 35 +/- 5 mmHg for 90 min, followed by resuscitation) and sacrificed 2 h thereafter. A marked increase in serum alpha-glutathione transferase, TNF-alpha, IL-6, IL-10, MCP-1, and MIP-1alpha and Kupffer cell cytokine production was observed in WT T-H mice compared with shams or control. In addition lung and liver tissue edema and neutrophil infiltration (myeloperoxidase (MPO) content) was also increased following T-H in WT animals. These inflammatory markers were markedly attenuated in the MIP-1alpha KO mice following T-H. Furthermore, compared with 2 h, MPO activities at 24 and 48 h after T-H declined steadily in both WT and KO mice. However, normalization of MPO activities to sham levels within 24 h was seen in KO mice but not in WT mice. Thus, MIP-1alpha plays an important role in mediating the acute inflammatory response following T-H. In the absence of MIP-1alpha, acute inflammatory responses were attenuated; rapidly recovered and less remote organ injury was noted following T-H. Thus, interventions that reduce MIP-1alpha levels following T-H should be useful in decreasing the deleterious inflammatory consequence of trauma.

Epigenetic regulation of dendritic cell-derived interleukin-12 facilitates immunosuppression after a severe innate immune response

Patients who survive sepsis have significant deficiencies in their immune responses caused by poorly understood mechanisms. We have explored this phenomenon by studying dendritic cells (DCs) recovered from animals surviving severe peritonitis-induced sepsis, using the well-established cecal ligation and puncture (CLP) model. Immediately after the initiation of sepsis there is a depletion in DCs from the lung and spleen, which is followed by repopulation of these cells back to the respective organs. DCs recovered from surviving animals exhibited a significant and chronic suppression of interleukin-12 (IL-12), a key host defense cytokine. The suppression of DC-derived IL-12 persisted for at least 6 weeks after CLP and was not due to immunoregulatory cytokines, such as IL-10. Using chromatin immunoprecipitation (ChIP) techniques, we have shown that the deficiency in DC-derived IL-12 was due to epigenetic alterations. Specifically, IL-12 expression was regulated by stable reciprocal changes in histone H3 lysine-4 trimethylation (H3K4me3) and histone H3 lysine-27 dimethylation (H3K27me2), as well as changes in cognate histone methyltransferase (HMT) complexes on the Il12p35 and Il12p40 promoters. These data implicate histone modification enzymes in suppressing DC-derived IL-12, which may provide one of the mechanisms of long-term immunosuppression subsequent to the septic response.

Dendritic cells at the interface of innate and acquired immunity: the role for epigenetic changes

Dendritic cells (DC) are known to be essential immune cells in innate immunity and in the initiation of adaptive immunity. The shaping of adaptive immunity by innate immunity is dependent on DC unique cellular functions and DC-derived effector molecules such as cytokines and chemokines. Thus, it is not surprising that numerous studies have identified alterations in DC number, function, and subset ratios in various diseases, such as infections, cancers, and autoimmune diseases. Recent evidence has also identified that immunosuppression occurring after severe systemic inflammation, such as found in sepsis, is a result of depletion in DC numbers and a later dysfunction in DC activity. This correlation suggests that the sustained DC dysfunction initiated by life-threatening inflammation may contribute to the subsequent immunoparalysis, potentially as a result of the long-term maintenance of an abnormal gene expression pattern. In this review, we summarized the present information regarding altered DC function after a severe, acute inflammatory response and propose a mechanism, whereby epigenetic changes can influence long-term gene expression patterns by DC, thus supporting an immunosuppression phenotype.

A MODEL OF MYOCARDIAL INFLAMMATION AND DYSFUNCTION IN BURN COMPLICATED BY SEPSIS

Numerous studies have described that an initial injury alters immune function, disposing the injured subject to infectious complications. The mechanisms by which an initial injury primes the subject, exacerbating the responses to a second injury, remain unclear; however, inflammatory cytokines have been implicated. The development of "2-hit" models has allowed investigators to determine the role of inflammatory mediators in susceptibility to infection after injury. A high incidence rate of pneumonia after burn injury and a significant increase in postburn mortality led us to develop models of either Gram-positive (Streptococcus pneumoniae) or Gram-negative (Klebsiella pneumoniae) sepsis after burn injury on 40% of total body surface area in rodents. In this present model, we used adult Sprague-Dawley rats to evaluate cardiac function in vitro (using Langendorff method) and myocardial inflammation (myocyte secretion of cytokines measured using enzyme-linked immunosorbent assay) after burn complicated by sepsis. Either burn injury alone or sepsis alone produced myocardial inflammatory responses and contractile dysfunction. Either Gram-negative or Gram-positive infection exacerbated the myocardial inflammation (increased myocyte secretion of tumor necrosis factor alpha, interleukin 1beta, and interleukin 6) above that which occurred with burn alone or with infection alone. Burn complicated by sepsis exacerbated the myocardial contraction and relaxation defects observed with either sepsis alone or burn alone. Inasmuch as sepsis, which occurs after a previous injury, increases myocardial inflammation/dysfunction and mortality, the development of therapeutic strategies that either decrease inflammatory response to the initial injury or provide cardiac support during the postinjury period may improve the outcome in injured patients who are at risk for developing sepsis.

Melatonin as pharmacologic support in burn patients: a proposed solution to thermal injury-related lymphocytopenia and oxidative damage

OBJECTIVE

To review the data that support the clinical use of melatonin in the treatment of burn patients, with special emphasis on the stimulation of the oxidative defense system, the immune system, circadian rhythm of sleep/wakefulness, and the reduction in the toxicity of therapeutic agents used in the treatment of burn victims.

DATA SOURCE

A MEDLINE/PubMed search from 1975 to July 2006 was conducted.

STUDY SELECTION

The screening of the literature was examined using the key words: burn patients, lymphocytopenia, skin oxidative stress, antioxidant, melatonin, and free radicals.

DATA EXTRACTION AND SYNTHESIS

Thermal injury often causes damage to multiple organs remote from the original burn wound and may lead to multiple organ failure. Animal models and burn patients exhibit elevated free radical generation that may be causative in the local wound response and in the development of burn shock and distant organ injury. The suppression of nonspecific resistance and the disturbance in the adaptive immune system makes burn patients vulnerable to infections. Moreover, there is loss of sleep and the toxicity produced by drugs habitually used in the clinic for burn patients. Melatonin is a powerful antioxidant and is a potent protective agent against damage after experimental thermal injury. Some actions of melatonin as a potential supportive pharmacologic agent in burn patients include its: role as a scavenger of both oxygen and nitrogen-based reactants, stimulation of the activities of a variety of antioxidative enzymes, reduction in proinflammatory cytokines, inhibition of adhesion molecules, chronobiotic effects, and reduction in the toxicity of the drugs used in protocols to treat thermal injury patients.

CONCLUSIONS

These combined actions of melatonin, along with its low toxicity and its ability to penetrate all morphophysiologic membranes, could make it a ubiquitously acting and highly beneficial molecule in burn patients.

Effect of Aspiration Pneumonia-Induced Sepsis on Post-Burn Cardiac Inflammation and Function in Mice

INTRODUCTION

Numerous studies have found that burn injury alters immune function, predisposing the subject to infectious complications. We developed a mouse model of burn injury complicated by either gram-positive or gram-negative infection and hypothesized that post-burn infection would exacerbate the myocardial cytokine responses and contractile dysfunction characteristic of either sepsis alone or burn alone.

METHODS

Adult C57 BL6 mice were given burn injury over 40% of the total body surface area and conventional fluid resuscitation (lactated Ringer's solution, 4 mL/kg/% burn) followed on day 7 by intratracheal administration of 1 x 10(5) cfu of either Streptococcus pneumoniae or Klebsiella pneumoniae or saline. Mice received fluid resuscitation (2 mL of lactated Ringer's intraperitoneally) again after bacterial challenge. Cardiomyocyte cytokine secretion and the contractile function of isolated hearts (Langendorff perfusion) were examined in vitro 24 h after bacterial challenge.

RESULTS

Infectious challenge seven days after burn injury exaggerated the inflammatory cytokine responses over those observed with either burn alone or gram-positive or gram-negative infection alone (tumor necrosis factor-alpha: sham, 72 +/- 9 pg/mL; burn alone, 176 +/- 6 pg/mL, Klebsiella pneumoniae alone, 337 +/- 8 pg/mL; Streptococcus pneumoniae alone, 184 +/- 2 pg/mL; burn + Klebsiella, 476 +/- 14 pg/mL; burn + Streptococcus, 351 +/- 6 pg/mL). Myocardial contractile depression was evident in the burn alone, infection alone, and burn plus infection groups, regardless of the organism selected to produce pneumonia-related sepsis.

CONCLUSIONS

Gram-negative or gram-positive infection exacerbated the myocardial inflammation seen with burn alone or infection alone. The availability of a mouse model of burn injury complicated by pneumonia-related sepsis will allow use of genetically engineered mice to examine further the mechanisms by which burn injury increases susceptibility to infection.

Enhanced regulatory T cell activity is an element of the host response to injury

CD4+CD25+ regulatory T cells (Tregs) play a critical role in suppressing the development of autoimmune disease, in controlling potentially harmful inflammatory responses, and in maintaining immune homeostasis. Because severe injury triggers both excessive inflammation and suppressed adaptive immunity, we wished to test whether injury could influence Treg activity. Using a mouse burn injury model, we demonstrate that injury significantly enhances Treg function. This increase in Treg activity is apparent at 7 days after injury and is restricted to lymph node CD4+CD25+ T cells draining the injury site. Moreover, we show that this injury-induced increase in Treg activity is cell-contact dependent and is mediated in part by increased cell surface TGF-beta1 expression. To test the in vivo significance of these findings, mice were depleted of CD4+CD25+ T cells before sham or burn injury and then were immunized to follow the development of T cell-dependent Ag-specific immune reactivity. We observed that injured mice, which normally demonstrate suppressed Th1-type immunity, showed normal Th1 responses when depleted of CD4+CD25+ T cells. Taken together, these observations suggest that injury can induce or amplify CD4+CD25+ Treg function and that CD4+CD25+ T cells contribute to the development of postinjury immune suppression.

Immunological control of methicillin-resistant Staphylococcus aureus (MRSA) infection in an immunodeficient murine model of thermal injuries

Staphylococcus aureus, especially methicillin-resistant S. aureus (MRSA), is a major cause of sepsis in patients who are immunosuppressed by their burns. In this study, an immunological regulation of MRSA infection was attempted in a mouse model of thermal injury. SCIDbg mice were resistant to MRSA infection, while SCIDbgMN mice (SCIDbg mice depleted of neutrophils and macrophages (Mphi)) were susceptible to the same infection. Also, thermally injured SCIDbg mice were shown to be susceptible to MRSA infection. On the other hand, the resistance of SCIDbgMN mice to the infection was completely recovered after an inoculation with Mphi from normal mice. However, anti-MRSA resistance was not shown in SCIDbgMN mice inoculated with Mphi from thermally injured mice. Mphi from MRSA-infected thermally injured mice were identified as alternatively activated Mphi, and Mphi from MRSA-infected unburned mice were characterized as classically activated Mphi. Mphi from thermally injured SCIDbg mice previously treated with 2-carboxyethylgermanium sesquioxide (Ge-132) protected SCIDbgMN mice against MRSA infection. Ge-132 has been described as an inhibitor of alternatively activated Mphi generation. These results suggest that MRSA infection in thermally injured patients is controlled immunologically through the induction of anti-MRSA effector cells and elimination of burn-associated alternatively activated Mphi, which are cells that inhibit the generation of classically activated Mphi.

Treatment with bindarit, a blocker of MCP-1 synthesis, protects mice against acute pancreatitis

Chemokines are believed to play a key role in the pathogenesis of acute pancreatitis. We have earlier shown that pancreatic acinar cells produce the chemokine monocyte chemotactic protein (MCP)-1 in response to caerulein hyperstimulation, demonstrating that acinar-derived MCP-1 is an early mediator of inflammation in acute pancreatitis. Blocking chemokine production or action is a major target for pharmacological intervention in a variety of inflammatory diseases, such as acute pancreatitis. 2-Methyl-2-[[1-(phenylmethyl)-1H-indazol-3yl]methoxy]propanoic acid (bindarit) has been shown to preferentially inhibit MCP-1 production in vitro in monocytes and in vivo without affecting the production of the cytokines IL-1, IL-6, or the chemokines IL-8, protein macrophage inflammatory-1alpha, and RANTES. The present study aimed to define the role of MCP-1 in acute pancreatitis with the use of bindarit. In a model of acute pancreatitis induced by caerulein hyperstimulation, prophylactic as well as therapeutic treatment with bindarit significantly reduced MCP-1 levels in the pancreas. Also, this treatment significantly protected mice against acute pancreatitis as evident by attenuated hyperamylasemia neutrophil sequestration in the pancreas (pancreatic MPO activity), and pancreatic acinar cell injury/necrosis on histological examination of pancreas sections.

Pathophysiology of acute pancreatitis

Acute pancreatitis is a common clinical condition. It is a disease of variable severity in which some patients experience mild, self-limited attacks while others manifest a severe, highly morbid, and frequently lethal attack. The exact mechanisms by which diverse etiological factors induce an attack are still unclear. It is generally believed that the earliest events in acute pancreatitis occur within acinar cells. Acinar cell injury early in acute pancreatitis leads to a local inflammatory reaction. If this inflammatory reaction is marked, it leads to a systemic inflammatory response syndrome (SIRS). An excessive SIRS leads to distant organ damage and multiple organ dysfunction syndrome (MODS). MODS associated with acute pancreatitis is the primary cause of morbidity and mortality in this condition. Recent studies have established the role played by inflammatory mediators in the pathogenesis of acute pancreatitis and the resultant MODS. At the same time, recent research has demonstrated the importance of acinar cell death in the form of apoptosis and necrosis as a determinant of pancreatitis severity. In this review, we will discuss about our current understanding of the pathophysiology of acute pancreatitis.

Influence of systemic inflammatory response syndrome on host resistance against bacterial infections*

OBJECTIVE

To determine the relationship between systemic inflammatory response syndrome (SIRS) and host innate immunities against bacterial infections.

DESIGN

Controlled animal study.

SETTING

University research laboratory.

SUBJECTS

Male BALB/c mice, 8-10 wks of age.

INTERVENTIONS

Morbidity and mortality rates of severe SIRS mice were compared with those of mild SIRS mice after infection with Enterococcus faecalis or methicillin-resistant Staphylococcus aureus (MRSA) or exposure to infectious complications induced by cecal ligation and puncture (CLP). In addition, a function of effector cells related to antibacterial innate immunities for these infections was analyzed in these two groups. Furthermore, SCIDbgMN mice (SCIDbg mice depleted of antibacterial effector cells) were reconstituted with effector cells from mild or severe SIRS mice and exposed to various infections.

MEASUREMENTS AND MAIN RESULTS

Severe SIRS mice were greatly susceptible to E. faecalis, MRSA, and CLP-induced sepsis. On the other hand, as compared with normal mice, mild SIRS mice were resistant to these infections. All of SCIDbgMN mice inoculated with peritoneal macrophages (PMphi) from severe SIRS mice died after infection with E. faecalis or MRSA, whereas all SCIDbgMN mice inoculated with PMphi from mild SIRS mice survived after the same infection. SCIDbgMN mice that were inoculated with PMphi from normal mice and exposed to E. faecalis, MRSA, or CLP survived at rates of 50%, 50%, or 60%, respectively. PMphi from mild SIRS mice exhibited typical properties for classically activated macrophages (CAMphi), whereas those from severe SIRS mice exhibited typical properties for alternatively activated macrophages (AAMphi).

CONCLUSIONS

Mphi-associated host antibacterial innate immunities are greatly influenced by SIRS levels. CAMphi, effector cells for the antibacterial innate immunity against E. faecalis, MRSA, and CLP-induced sepsis, are induced in mild SIRS mice. AAMphi with no antibacterial capabilities are generated in mice with severe SIRS. Induction of CAMphi may protect severe SIRS patients against infections.

CCL2, a product of mice early after systemic inflammatory response syndrome (SIRS), induces alternatively activated macrophages capable of impairing antibacterial resistance of SIRS mice

Infection associated with systemic inflammatory response syndrome (SIRS) is a major cause of morbidity and mortality in patients with major surgery, polytrauma, and severe burn injury. In previous studies, mice with severe pancreatitis (a mouse model of SIRS, SIRS mice) have been shown to be greatly susceptible to various infections. In the present study, a mechanism involved in the impaired resistance of SIRS mice to infectious complications was investigated. Sera from SIRS mice impaired the resistance of normal mice to infectious complications induced by cecal ligation and puncture (CLP). CC chemokine ligand 2 (CCL2) was detected in sera of SIRS mice. Resident macrophages (RMphi) cultured with SIRS mouse sera converted to alternatively activated macrophages (AAMphi), which were also demonstrated in mice treated with recombinant murine CCL2. However, AAMphi were not demonstrated in mice injected with SIRS mouse sera and anti-CCL2 monoclonal antibody (mAb) in combination. Furthermore, normal mice that received SIRS mouse sera and anti-CCL2 mAb resisted CLP-induced infectious complications. These results indicate that the resistance of SIRS mice to infectious complications is impaired by AAMphi generated from RMphi in response to SIRS-associated CCL2 production.

The chronic consequences of severe sepsis

The early events of severe sepsis set in motion a cascade of events that significantly contributes to the morbidity and mortality observed during the first few days of this syndrome. Although sepsis is a deadly, acute disease, survivors also suffer long-term consequences. Clinical data underscore subsequent high mortality rates associated with patients who are long-term survivors of the acute septic episode. Within 1 year of surviving severe sepsis, there is a 26% predicted mortality rate, and many patients succumb to lung complications. In this review, we focus on the cellular and molecular mechanisms that dictate the longer-term sequela of sepsis and related lung injury. We have established a murine model of experimental sepsis [cecal ligation and puncture (CLP)], which results in an approximate 60% survival rate. Our studies have demonstrated that these survivors are susceptible to a fungal infection with 100% mortality when challenged 3 days or 15 days post-recovery from the initial CLP. This increased mortality correlates with changes in cytokines and Toll-like receptor expression and alterations in lung leukocyte populations. We hypothesize that the lung becomes predisposed to nosocomial infections for extended periods of time after severe sepsis via mechanisms that include alterations in inflammatory cytokines and an increase in immunomodulatory chemokines, such as monocyte chemoattractant protein-1 and C10. These mediators may alter the innate-immune response by affecting dendritic cells and macrophages, which could provide a mechanism for the immunosuppression observed following sepsis.

Mast cells and resistance to peritoneal sepsis after burn injury

A mouse model of burn injury demonstrates increasing mortality to an infectious challenge in the form of cecal ligation and puncture (CLP) reaching a peak at 10 days after injury. Because it is widely believed that peritoneal mast cells play an important role in the defense against peritoneal sepsis, we wished to explore the possibility that peritoneal mast cell dysfunction contributed to increased CLP mortality after burn injury. Kit(W-v) C57BL/6 mice, which were shown to lack peritoneal mast cells by cytospin and flow cytometry, and normal littermate control animals were subjected to 25% burn or sham burn injury and 10 days later underwent CLP. Burn injured Kit(W-v) and normal littermates had a high CLP mortality when compared with sham-injured Kit(W-v) and normal littermates (P < 0.003), but the sham- and burn-injured Kit(W-v) and normal littermate animals did not differ from one another with respect to CLP mortality. This result prompted a comparison of CLP mortality in untreated WBB6F1 Kit(W/W-v) mice, known to be mast cell deficient, and normal littermate controls, as well as untreated C57BL/6 Kit(W-v) and normal littermates. The WBB6F1 Kit(W/W-v) mice showed significantly increased mortality after CLP as compared with the littermate controls (P = 0.03), whereas both C57BL/6 Kit(W-v) and littermate controls had very low mortality after CLP. A study of peritoneal cell populations 24 h after CLP failed to reveal an obvious cause for the difference in CLP survival between the two mast cell-deficient strains. Tumor necrosis factor-alpha (TNF-alpha) measurements in peritoneal fluid showed appreciable amounts of TNF-alpha in the littermate controls of both strains and little in the fluid obtained from the mast cell-deficient animals of both strains. We conclude that peritoneal mast cell dysfunction is unlikely to be a major cause of decreased resistance to peritoneal sepsis in burn-injured animals and that the importance of peritoneal mast cells in combating peritoneal sepsis in the mouse appears to be strain dependent.