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

Unremitting pro-inflammatory T-cell phenotypes, and macrophage activity, following paediatric burn injury

Objectives

The aim of this study was to characterise the dynamic immune profile of paediatric burn patients for up to 18 months post-burn.

Methods

Flow cytometry was used to measure 25 cell markers, chemokines and cytokines which reflected both pro-inflammatory and anti-inflammatory immune profiles. Peripheral blood mononuclear cells from 6 paediatric burn patients who had returned for repeated burn and scar treatments for > 4 timepoints within 12 months post-burn were compared to four age-matched healthy controls.

Results

While overall proportions of T cells, NK cells and macrophages remained relatively constant, over time percentages of these immune cells differentiated into effector and proinflammatory cell phenotypes including Th17 and activated γδ T cells. Circulating proportions of γδ T cells increased their expression of pro-inflammatory mediators throughout the burn recovery, with a 3-6 fold increase of IL-17 at 1-3 weeks, and NFκβ 9-18 months post-burn. T-regulatory cell plasticity was also observed, and Treg phenotype proportions changed from systemically reduced skin-homing T-regs (CCR4+) and increased inflammatory (CCR6+) at 1-month post-burn, to double-positive cell types (CCR4+CCR6+) elevated in circulation for 18 months post-burn. Furthermore, Tregs were observed to proportionally express less IL-10 but increased TNF-α over 18 months.

Conclusion

Overall, these results indicate the circulating percentages of immune cells do not increase or decrease over time post-burn, instead they become highly specialised, inflammatory and skin-homing. In this patient population, these changes persisted for at least 18 months post-burn, this 'immune distraction' may limit the ability of immune cells to prioritise other threats post-burn, such as respiratory infections.

Accelerated Burn Healing in a Mouse Experimental Model Using α-Gal Nanoparticles

Macrophages play a pivotal role in the process of healing burns. One of the major risks in the course of burn healing, in the absence of regenerating epidermis, is infections, which greatly contribute to morbidity and mortality in such patients. Therefore, it is widely agreed that accelerating the recruitment of macrophages into burns may contribute to faster regeneration of the epidermis, thus decreasing the risk of infections. This review describes a unique method for the rapid recruitment of macrophages into burns and the activation of these macrophages to mediate accelerated regrowth of the epidermis and healing of burns. The method is based on the application of bio-degradable "α-gal" nanoparticles to burns. These nanoparticles present multiple α-gal epitopes (Galα1-3Galβ1-4GlcNAc-R), which bind the abundant natural anti-Gal antibody that constitutes ~1% of immunoglobulins in humans. Anti-Gal/α-gal nanoparticle interaction activates the complement system, resulting in localized production of the complement cleavage peptides C5a and C3a, which are highly effective chemotactic factors for monocyte-derived macrophages. The macrophages recruited into the α-gal nanoparticle-treated burns are activated following interaction between the Fc portion of anti-Gal coating the nanoparticles and the multiple Fc receptors on macrophage cell membranes. The activated macrophages secrete a variety of cytokines/growth factors that accelerate the regrowth of the epidermis and regeneration of the injured skin, thereby cutting the healing time by half. Studies on the healing of thermal injuries in the skin of anti-Gal-producing mice demonstrated a much faster recruitment of macrophages into burns treated with α-gal nanoparticles than in control burns treated with saline and healing of the burns within 6 days, whereas healing of control burns took ~12 days. α-Gal nanoparticles are non-toxic and do not cause chronic granulomas. These findings suggest that α-gal nanoparticles treatment may harness anti-Gal for inducing similar accelerated burn healing effects also in humans.

Targeted multi-omic analysis of human skin tissue identifies alterations of conventional and unconventional T cells associated with burn injury

Burn injuries are a leading cause of unintentional injury, associated with a dysfunctional immune response and an increased risk of infections. Despite this, little is known about the role of T cells in human burn injury. In this study, we compared the activation and function of conventional T cells and unconventional T cell subsets in skin tissue from acute burn (within 7 days from initial injury), late phase burn (beyond 7 days from initial injury), and non-burn patients. We compared T cell functionality by a combination of flow cytometry and a multi-omic single-cell approach with targeted transcriptomics and protein expression. We found a significantly lower proportion of CD8+ T cells in burn skin compared to non-burn skin, with CD4+ T cells making up the bulk of the T cell population. Both conventional and unconventional burn tissue T cells show significantly higher IFN-γ and TNF-α levels after stimulation than non-burn skin T cells. In sorted T cells, clustering showed that burn tissue had significantly higher expression of homing receptors CCR7, S1PR1, and SELL compared to non-burn skin. In unconventional T cells, including mucosal-associated invariant T (MAIT) and γδ T cells, we see significantly higher expression of cytotoxic molecules GZMB, PRF1, and GZMK. Multi-omics analysis of conventional T cells suggests a shift from tissue-resident T cells in non-burn tissue to a circulating T cell phenotype in burn tissue. In conclusion, by examining skin tissue from burn patients, our results suggest that T cells in burn tissue have a pro-inflammatory rather than a homeostatic tissue-resident phenotype, and that unconventional T cells have a higher cytotoxic capacity. Our findings have the potential to inform the development of novel treatment strategies for burns.

Protocol for clinical diagnosis and empiric treatment of pulmonary tuberculosis in severely burned patients: observations and literature review

Introduction

Reactivation of pulmonary tuberculosis is a prevalent concomitant infection and cause for mortality in burns patients in Sub-Saharan Africa. First line laboratory diagnostic studies for pulmonary tuberculosis are often negative in these patients and if relied on, result in high mortality. The purpose of this report is to share our experience with a novel protocol of empiric treatment of clinically suspected pulmonary tuberculosis in severely burned patients with negative GeneXpert tests in a tertiary burns centre and to present a brief literature review on the topic.

Methods

A retrospective chart review of all patients, who sustained thermal injury with an inhalation component, with negative GeneXpert tests who were treated empirically for pulmonary tuberculosis over a five-year period (2015-2020) was performed. Additionally, a literature search was performed on Medline (PubMed), Cochrane and Google Scholar databases.

Results

Over the five-year period, 20 patients with suspected pulmonary tuberculosis and severe burns requiring ventilation were managed according to the protocol and all survived to discharge. The literature search identified six factors that explain the consequence of pulmonary tuberculosis in severely burned patients and provide a hypothesis for the negative laboratory studies encountered.

Conclusion

There was an improved outcome for patients with the clinical diagnosis of reactivation of pulmonary tuberculosis when they were started on empirical pulmonary tuberculosis treatment. There are several potential mechanisms that can contribute to reactivation of pulmonary tuberculosis in susceptible severely burned patients. The GeneXpert test should not be relied upon in these patients for a diagnosis, but rather all other clinical evidence should inform management.

Lay Summary

From the current literature evidence most patients who have severe burns complicated by a secondary infection known as pulmonary (lung) tuberculosis, die as a result. The purpose of this report is to share our experience with treatment of pulmonary tuberculosis during a five-year period, from 2015 to 2020, in a specialized adult tertiary burn center. Severely burned patients who were suspected of having pulmonary tuberculosis and received treatment despite having negative laboratory tests for pulmonary tuberculosis, had a better survival rate than expected. A brief literature review on the topic of pulmonary tuberculosis and severe burns was done to investigate causes for reactivation of pulmonary tuberculosis and negative laboratory studies in these patients.The literature search identified the following factors that can potentially affect the reactivation of pulmonary tuberculosis in severely burned patients: decreased immune system; secondary infections; low blood albumin(protein) levels; decreased clearance of bacteria from the airways, the development of pulmonary tuberculosis biofilms (capsules that protect the bacteria from chemicals and antibiotics) and the role of a fat molecule called phosphatidylinositol mannoside in pulmonary tuberculosis.In conclusion, the pulmonary tuberculosis test should not be relied upon in these patients, but rather all the clinical evidence such X-ray changes in association with difficulty to wean the patient off the ventilator should be used to inform treatment choice.

Burn injury is associated with an infiltration of the wound site with myeloid-derived suppressor cells

Myeloid-derived suppressor cells (MDSCs) have been identified in the burn wound, however their characterization is incomplete. To study this, mice were subjected to a major burn and skin cells were isolated 3 days thereafter for analysis. Significant infiltration of the burn wound with MDSCs was observed as compared with uninjured skin. The skin of naïve mice did not contain MDSCs. Characterization of the cells showed that 33% of MDSCs in the wound were monocytic (M)-MDSCs, which was significantly less than that found in uninjured skin (52%). In contrast, polymorphonuclear (PMN)-MDSCs were greater in the burn wound as compared with uninjured skin. Burn wound TLR expression by both MDSCs subsets was decreased as compared with uninjured skin. Wound MDSCs produced pro- and anti-inflammatory cytokines and iNOS was present in both MDSC subsets, whereas ARG1 was only present in M-MDSCs. In conclusion, both M- and PMN-MDSCs infiltrate burn wound with after injury, however, they displayed decreased TLR expression, suggesting receptor down-regulation.

Burn and thoracic trauma alters fracture healing, systemic inflammation, and leukocyte kinetics in a rat model of polytrauma

Background

Singular traumatic insults, such as bone fracture, typically initiate an appropriate immune response necessary to restore the host to pre-insult homeostasis with limited damage to self. However, multiple concurrent insults, such as a combination of fracture, blunt force trauma, and burns (polytrauma), are clinically perceived to result in abnormal immune response leading to inadequate healing and resolution. To investigate this phenomenon, we created a model rat model of polytrauma.

Methods

To investigate relationship between polytrauma and delayed healing, we created a novel model of polytrauma in a rat which encompassed a 3-mm osteotomy, blunt chest trauma, and full-thickness scald burn. Healing outcomes were determined at 5 weeks where the degree of bone formation at the osteotomy site of polytrauma animals was compared to osteotomy only animals (OST).

Results

We observed significant differences in the bone volume fraction between polytrauma and OST animals indicating that polytrauma negatively effects wound healing. Polytrauma animals also displayed a significant decrease in their ability to return to pre-injury weight compared to osteotomy animals. Polytrauma animals also exhibited significantly altered gene expression in osteogenic pathways as well as the innate and adaptive immune response. Perturbed inflammation was observed in the polytrauma group compared to the osteotomy group as evidenced by significantly altered white blood cell (WBC) profiles and significantly elevated plasma high-mobility group box 1 protein (HMGB1) at 6 and 24 h post-trauma. Conversely, polytrauma animals exhibited significantly lower concentrations of plasma TNF-alpha (TNF-α) and interleukin 6 (IL-6) at 72 h post-injury compared to OST.

Conclusions

Following polytrauma with burn injury, the local and systemic immune response is divergent from the immune response following a less severe singular injury (osteotomy). This altered immune response that follows was associated with a reduced capacity for wound healing.

Electronic supplementary material

The online version of this article (10.1186/s13018-019-1082-4) contains supplementary material, which is available to authorized users.

Nrf2 plays a pivotal role in protection against burn trauma-induced intestinal injury and death

Nuclear factor (erythroid-derived 2)-like 2 (NRF2) is a basic leucine zipper transcription factor that principally defends against oxidative stress and also plays a unique role in severe sepsis. However, its contribution to intestinal injury and death after burn trauma is unclear.In this study, wild-type (Nrf2+/+) and Nrf2-deficient (Nrf2-/-) mice were subjected to 15% or 30% total body surface area burn or sham injury. Survival, systemic inflammation, and gut injury were determined.Nrf2-/- mice were more susceptible to burn-induced intestinal injury, as characterized by increases in damage to the gut structure and in intestinal permeability. This exacerbation was associated with an increase in the intestinal mRNA expression of inflammatory cytokines (interleukin [IL]-6, IL-1B, monocyte chemotactic protein 1, intercellular adhesion molecule, and vascular cell adhesion molecule) and a decrease in the intestinal mRNA expression of Nrf2-regulated genes (NAD(P)H dehydrogenasequinine-1 and glutamate-cysteine ligase modifier subunit). Nrf2-deficient mice also showed a lower survival rate and higher levels of systemic cytokines (IL-6 and IL-1B) and high-mobility group protein B1 than wild-type mice. This study demonstrates for the first time that mice that lack Nrf2 are more susceptible to burn-induced intestinal injury and have more systemic inflammation and a lower survival rate.

To cross-link or not to cross-link? Cross-linking associated foreign body response of collagen-based devices

Collagen-based devices, in various physical conformations, are extensively used for tissue engineering and regenerative medicine applications. Given that the natural cross-linking pathway of collagen does not occur in vitro, chemical, physical, and biological cross-linking methods have been assessed over the years to control mechanical stability, degradation rate, and immunogenicity of the device upon implantation. Although in vitro data demonstrate that mechanical properties and degradation rate can be accurately controlled as a function of the cross-linking method utilized, preclinical and clinical data indicate that cross-linking methods employed may have adverse effects on host response, especially when potent cross-linking methods are employed. Experimental data suggest that more suitable cross-linking methods should be developed to achieve a balance between stability and functional remodeling.

Gamma delta T cells regulate wound myeloid cell activity after burn

Major burns induce immune complications, which are associated with myeloid cell activation by ill-defined mechanisms. Although γδ T cells have been shown to be important in postinjury inflammation and wound healing, their role in the regulation of myeloid cells remains unknown. To study this, wild-type (WT) and γδ T cell-deficient (δTCR) mice were subjected to major burn (25% total body surface area, third degree) or sham treatment. At 3 days thereafter, skin samples were assayed for cytokine content or used to isolate single cells that were used for myeloid cell characterization by flow cytometry. The number of CD11b myeloid cells increased by approximately 75% in the wound skin of WT mice. This influx was caused by increased myeloid-derived suppressor cells (CD11b GR1) whose numbers increased 19-fold compared with those of sham skin. In contrast, macrophage (MØ; CD11b F4/80) numbers decreased by approximately 50% after burn. In δTCR mice, burn increased the myeloid cell numbers approximately 5-fold. The increase in myeloid cells at the injury site of δTCR mice was caused by both a myeloid-derived suppressor cell (50-fold) and a MØ (2-fold) influx. Burn increased skin cytokine levels for a number of prototypic inflammatory cytokines (interleukin 1β, interleukin 6, tumor necrosis factor-α, macrophage inflammatory protein [MIP] 1β, etc). Tumor necrosis factor-α, MIP-1α, and MIP-1β levels were further elevated (2- to 3-fold) in the injured skin of δTCR mice compared with those of WT mice. In conclusion, these data show that γδ T cells regulate myeloid cell infiltration of the wound site and act to quell inflammation, thereby promoting the transition to the proliferative phase of wound healing.

A novel subpopulation of peripheral blood mononuclear cells presents in major burn patients

Hypertrophic scars (HTS) are generally believed to result from proliferation and activation of resident connective tissue fibroblasts after burns. To demonstrate a potential role of blood-borne cells, the peripheral blood mononuclear cells (PBMCs) and the effect of PBMCs on dermal fibroblast behavior was investigated. Flow cytometry was used to analyze the surface and intracellular protein expression of PBMCs and fibroblasts. Transwell migration assay, enzyme-linked immunosorbent assay and real-time reverse transcription polymerase chain reaction was performed to assess fibroblast functions. We identified a novel subpopulation of PBMCs in burn patients in vivo that appears at an early stage following major thermal injuries, which primarily express procollagen 1, leukocyte specific protein 1, CD204, toll-like receptor 4 and stromal cell-derived factor 1 (SDF-1) receptor CXCR4. In vitro, the conditioned media from burn patient PBMCs up-regulated the expression of fibrotic growth factors and extracellular matrix molecules, down-regulated antifibrotic factor decorin, enhanced cell chemotaxis and promoted cell differentiation into contractile myofibroblasts in dermal fibroblasts. After thermal injury, this novel subpopulation of PBMCs is systemically triggered and attracted to the wounds under SDF-1/CXCR4 signaling where they appear to modulate the functions of resident connective tissue cells and thus contribute to the development of HTS.

Interleukin-22 modulates gut epithelial and immune barrier functions following acute alcohol exposure and burn injury

Interleukin-22 (IL-22) maintains gut epithelial integrity and expression of antimicrobial peptides Reg3β and Reg3γ. Our laboratory has shown that acute alcohol/ethanol (EtOH) exposure before burn injury results in increased gut permeability, intestinal T-cell suppression, and enhanced bacterial translocation. Herein, we determined the effect of combined EtOH intoxication and burn injury on intestinal levels of IL-22 as well as Reg3β and Reg3γ expression. We further examined whether in vivo restitution of IL-22 restores gut permeability, Reg3β and Reg3γ levels, and bacterial load (e.g., gut bacterial growth) within the intestine after EtOH and burn injury. Male mice, ∼25g, were gavaged with EtOH (2.9 mg/kg) before receiving a ∼12.5% total-body-surface-area, full-thickness burn. Mice were immediately treated with saline control or IL-22 (1 mg/kg) by i.p. injection. One day after injury, there was a significant decrease in intestinal IL-22, Reg3β, and Reg3γ expression along with an increase in intestinal permeability and gut bacterial load after EtOH combined with burn injury, as compared with sham injury. Treatment with IL-22 normalized Reg3β and Reg3γ expression and attenuated the increase in intestinal permeability after EtOH and burn injury. Qualitatively, IL-22 treatment reduced the bacterial load in nearly half of mice receiving EtOH combined with burn injury. Our data indicate that IL-22 maintains gut epithelial and immune barrier integrity after EtOH and burn injury; thus, the IL-22/antimicrobial peptide pathway may provide a therapeutic target for the treatment of patients who sustain burn injury under the influence of EtOH.

Three-year review of bacteriological profile and antibiogram of burn wound isolates in Van, Turkey

The risk of infection in burns is well-known. In recent decades, the antimicrobial resistance of bacteria isolated from burn patients has increased. For this reason, a retrospective study was conducted at Van Training and Research Hospital to analyze the bacterial isolates from the wounds of patients admitted to the Burn Unit and to determine the susceptibility patterns of the commonly cultured organisms over a 3-year period, January 2009 to December 2011.A total of 250 microorganisms were isolated from burn wounds of 179 patients. Our results revealed that the most frequent isolate was Acinetobacter baumannii (23.6%), Pseudomonas aeruginosa (12%), Staphylococcus aureus (11.2%), Escherichia coli (10%) respectively. Multidrug-resistance has emerged as an important concern in our burn unit. Tigecycline, and colistin were found to be the most active drugs against Acinetobacter baumannii. Carbapenems and amikacin, were found to be the most active drugs against other gram negative bacteria. Vancomycin and linezolid were active against gram positive bacteria.Aggressive infection control measures should be applied to limit the emergence and spread of multidrug-resistant pathogens.

Gram-negative bacterial infection in thigh abscess can migrate to distant burn depending on burn depth

Sepsis remains the major cause of death in patients with major burn injuries. In the present investigation we evaluated the interaction between burn injuries of varying severity and preexisting distant infection. We used Gram-negative bacteria (Pseudomonas aeruginosa and Proteus mirabilis) that were genetically engineered to be bioluminescent, which allowed for noninvasive, sequential optical imaging of the extent and severity of the infection. The bioluminescent bacteria migrated from subcutaneous abscesses in the leg to distant burn wounds on the back depending on the severity of the burn injury, and this migration led to increased mortality of the mice. Treatment with ciprofloxacin, injected either in the leg with the bacterial infection or into the burn eschar, prevented this colonization of the wound and decreased mortality. The present data suggest that burn wounds can readily become colonized by infections distant from the wound itself.

Bacteriology of infected burn wounds in the burn wards of a teaching hospital in Southwest Nigeria

BACKGROUND

Burns are characterized by the loss of varying proportions of the protective layers of the skin, depression of immune responses, and increased wound susceptibility to infection. Wound infection is a major cause of morbidity and mortality in burn cases. This study characterizes those factors that predispose burn wounds to infection and the bacteriology of the microorganisms in our environment.

PATIENTS AND METHODS

Prospective study of burns patients that were admitted and treated at the Lagos State University Teaching Hospital (LASUTH), Ikeja-Lagos, Nigeria between January 1 and May 31, 2010 was carried out. Information about the demographics, aetiology/mechanism of burns, interval between the time of injury and admission, microbial studies, and antibiotic therapy were collected and analyzed.

RESULTS

A total of 74 patients consisting of 43 males and 31 females were seen. The ages range between one week and 95 ± 22.42 years. Wound infections were confirmed in 28 patients (infection rate of 37.84 per 100 patients). Delayed presentation at LASUTH and length of hospital stay were significantly related to the development of wound infection. Pseudomonas aeruginosa and Proteus mirabilis were the most common infective organisms occurring in 53.6 and 10.7 percentages respectively. The isolated organisms were resistant to the beta-lactam antibiotics and mostly sensitive to carbapenem and aztreonam preparations.

CONCLUSION

Factors predisposing to invasive wound infections in our environment were highlighted and suggestions made on methods that could reduce the infections and thus reduce morbidity and mortality in burns.

Injury induces early activation of T-cell receptor signaling pathways in CD4+ regulatory T cells

Although it is known that injury enhances the regulatory activity of CD4 regulatory T cells (Tregs), the cellular and molecular mechanisms responsible for injury-induced Treg activation remain unclear. This study was designed to investigate and compare injury-induced T-cell receptor (TCR) signaling in Tregs, non-Tregs, and CD8 T cells. Specifically, we used phospho-flow cytometry to measure the expression and phosphorylation of ZAP-70, protein kinase C θ, nuclear factor of activated T cells, and glycogen synthase kinase 3β in FoxP3 Tregs versus FoxP3 non-Tregs versus CD8 T cells. Groups of male C57BL/6J mice underwent burn or sham injury, and lymph nodes and spleens were harvested at early time points-15, 30, 60, 120, and 240 min-to measure TCR signaling. As early as 15 min after burn injury, we observed a significant upregulation and phosphorylation of ZAP-70, protein kinase C θ, nuclear factor of activated T cells, and glycogen synthase kinase 3β in Tregs prepared from injury-site-draining lymph nodes. Burn injury did not activate TCR signaling in Tregs from the spleen or in CD4 non-Tregs and CD8 T cells. In conclusion, the results of this study demonstrate that burn injury activates TCR signaling in Tregs, but not non-Tregs or CD8 T cells. These findings suggest that injury provides an early TCR-activating signal to Tregs and supply new insights into how injury influences the adaptive immune system.

Reproducible subcutaneous transplantation of cell sheets into recipient mice

Perfecting tissue engineering and cell sheet transplantation is an important step toward realizing regenerative medicine and is a growing area of research. Before being applied to clinical settings, it is important that these approaches are evaluated in vivo. Here we provide a detailed protocol for handling thin cell sheets, for a simple and highly reproducible subcutaneous transplantation of cell sheets into mice, and for the histological examination of regenerated tissues. Various aspects of transplants can be assessed, such as maintenance, differentiation and proliferation. An emphasis is placed on surgical precision and reproducibility. The resulting consistency between surgeries helps minimize artifacts from surgical variation and therefore enables researchers to not only observe and compare the interactions between host tissues but also to compare transplants among different host animals. A single transplantation can be carried out within ∼10 min.

Burn-induced alterations in toll-like receptor-mediated responses by bronchoalveolar lavage cells

Burn is associated with profound inflammation and activation of the innate immune system in multiple organ beds, including the lung. Similarly, toll-like receptors (TLR) are associated with innate immune activation. Nonetheless, it is unclear what impact burn has on TLR-induced inflammatory responses in the lung.

METHODS

Male C57BL/6 mice were subjected to burn (3rd degree, 25% TBSA) or sham procedure and 1, 3 or 7 days thereafter, bronchoalveolar lavage (BAL) fluid was collected and cells were isolated and cultured in vitro with specific TLR agonists as follows: Zymosan (TLR-2), LPS (TLR-4) and CpG-ODN (TLR-9). Supernatants were collected 48 h later and assayed for inflammatory cytokine levels (IL-1β, IL-6, IL-10, IL-17, TNF-α, KC, MCP-1, MIP-1α, MIP-1β and RANTES) by Bioplex.

RESULTS

BAL fluid from sham and burn mice did not contain detectable cytokine levels. BAL cells, irrespective of injury, were responsive to TLR-2 and TLR-4 activation. Seven days after burn, TLR-2 and TLR-4 mediated responses by BAL cells were enhanced as evidenced by increased production of IL-6, IL-17, TNF-α, MCP-1, MIP-1β and RANTES.

CONCLUSIONS

Burn-induced changes in TLR-2 and TLR-4 reactivity may contribute to the development of post-burn complications, such as acute lung injury (ALI) and adult respiratory distress syndrome (ARDS).

Burn induces a Th-17 inflammatory response at the injury site

INTRODUCTION

The high incidence of morbidity and mortality following major burn can be in part attributed to immune dysfunction and wound healing complications. Inflammation plays a major role in the complex process of wound repair. Recently, a novel class of T-helper cells, termed Th-17 cells, has been found to secrete the pro-inflammatory cytokines IL-17 and IL-22. The Th-17 response also involves other cytokines, such as IL-6 and TGF-β, which have been shown to be associated with burn-induced inflammation. Nonetheless, the relationships between the Th-17 response and post-burn inflammation are unknown.

METHODS

C57BL/6 male mice (n = 5-6/group) were subjected to a major burn (25% TBSA) or sham procedure. Three hours thereafter, skin samples were collected (uninjured skin and burn skin) and processed for the determination of Th-17 cytokine (IL-6, IL-17, IL-22, IL-23, IL-27, and TGF-β) levels by ELISA.

RESULTS

At 3h after burn a significant (~3-fold) increase in tissue levels of IL-17 and IL-22 was observed at the burn site as compared to sham skin. The burn-induced Th-17 response was independent of statistically significant changes in other Th-17 cytokines (i.e., IL-6, IL-23, IL-27 and TGF-β).

CONCLUSIONS

These findings indicate the development of a robust Th-17 response at the burn site that may play an important role in subsequent immune and wound healing derangements.

Increased expression of cardiac IL-17 after burn

Background

Cardiac dysfunction is a common complication associated with major burns. While recent findings have linked the Th-17 T-cell response to the development of autoimmune myocarditis, the role of IL-17 and the Th-17 T-cell response in the development of post-burn cardiac dysfunction remains unknown.

Methods

Male C57BL/6 mice were subjected to a major burn (3^rd degree, 25% TBSA) or sham treatment. Three hours after injury plasma and tissue (i.e., heart, lung, liver, small intestine) samples were collected and analyzed for the expression of Th-17 cytokine (i.e., IL-6, IL-17, IL-22, IL-23, TGF-β) levels by ELISA.

Results

Cardiac tissue levels of the Th-17 cytokines, IL-6, IL-17 and IL-22 were significantly elevated at 3 hrs after burn as compared to sham levels. IL-17 was analyzed 1, 3 and 7 days after burn and showed a return to baseline levels and without a difference in the burn group. Burn-induced alterations in the level of these cytokines in plasma or other tissues were not evident. The cardiac Th-17 cytokine response after burn injury was specific, as cardiac levels of Th-1 (IFN-γ) and Th-2 (IL-10) cytokines were not significantly affected after injury. The cardiac Th-17 response correlated with a significant increase in Troponin levels at 3 hr. after burn.

Conclusion

These findings indicate that early after burn, cardiac tissue is associated with significantly elevated levels of Th-17 cytokines. The early Th-17 response after burn appears to be specific for cardiac tissue and may promote myocardial inflammation and dysfunction associated with this form of trauma.

Early infection during burn-induced inflammatory response results in increased mortality and p38-mediated neutrophil dysfunction

Following burn injury, the host is susceptible to bacterial infections normally cleared by healthy patients. We hypothesized that during the systemic immune response that follows scald injury, the host's altered immune status increases infection susceptibility. Using a murine model of scald injury under inhaled anesthesia followed by intraperitoneal infection, we observed increased neutrophil numbers and function at postburn day (PBD) 1 compared with sham-burned and PBD4 mice. Further, increased mortality, bacteremia, and serum IL-6 were observed in PBD1 mice after Pseudomonas aeruginosa (PA) infection compared with sham-burned and PBD4 mice infected with PA. To examine these disparate responses, we investigated neutrophils isolated at 5 and 24 h following PA infection from PBD1 and sham-burned mice. Five hours after infection, there was no significant difference in number of recruited neutrophils; however, neutrophils from injured mice had decreased activation, active-p38, and oxidative burst compared with sham-burned mice. In direct contrast, 24 h after infection, we observed increased numbers, active-p38, and oxidative burst of neutrophils from PBD1 mice. Finally, we demonstrated that in neutrophils isolated from PBD1 mice, the observed increase in oxidative burst was p38 dependent. Altogether, neutrophil activation and function from thermally injured mice are initially delayed and later exacerbated by a p38-dependent mechanism. This mechanism is likely key to the observed increase in bacterial load and mortality of PBD1 mice infected with PA.

Wound trauma mediated inflammatory signaling attenuates a tissue regenerative response in MRL/MpJ mice

Background

Severe trauma can induce pathophysiological responses that have marked inflammatory components. The development of systemic inflammation following severe thermal injury has been implicated in immune dysfunction, delayed wound healing, multi-system organ failure and increased mortality.

Methods

In this study, we examined the impact of thermal injury-induced systemic inflammation on the healing response of a secondary wound in the MRL/MpJ mouse model, which was anatomically remote from the primary site of trauma, a wound that typically undergoes scarless healing in this specific strain. Ear-hole wounds in MRL/MpJ mice have previously displayed accelerated healing and tissue regeneration in the absence of a secondary insult.

Results

Severe thermal injury in addition to distal ear-hole wounds induced marked local and systemic inflammatory responses in the lungs and significantly augmented the expression of inflammatory mediators in the ear tissue. By day 14, 61% of the ear-hole wounds from thermally injured mice demonstrated extensive inflammation with marked inflammatory cell infiltration, extensive ulceration, and various level of necrosis to the point where a large percentage (38%) had to be euthanized early during the study due to extensive necrosis, inflammation and ear deformation. By day 35, ear-hole wounds in mice not subjected to thermal injury were completely closed, while the ear-hole wounds in thermally injured mice exhibited less inflammation and necrosis and only closed partially (62%). Thermal injury resulted in marked increases in serum levels of IL-6, TNFα, KC (CXCL1), and MIP-2α (CXCL2). Interestingly, attenuated early ear wound healing in the thermally injured mouse resulted in incomplete tissue regeneration in addition to a marked inflammatory response, as evidenced by the histological appearance of the wound and increased transcription of potent inflammatory mediators.

Conclusion

These findings suggest that the observed systemic inflammatory response of a severe thermal injury undoubtedly has an adverse effect on wound healing and tissue regeneration.

In vivo IL-18 supplementation ameliorates lethal acute lung injury in burn-primed endotoxemic mice: a novel anti-inflammatory role of IL-18

Previously, we have found that a prior burn insult induces lethal acute lung injury (ALI) and overproduction of proinflammatory cytokines after LPS challenge in mice. The current study was aimed to determine the role of IL-18 in burn-induced LPS hypersensitivity. Except sham group, mice were subjected to a 15% total body surface area full-thickness burn and either untreated or treated with IL-18 alone, IL-18 + anti-IL-10 antibody or IL-18 + isotype immunoglobulin G. LPS was intravenously administered to all mice on the 11th day, and the mice were killed at the indicated time point, or survival was examined. We additionally examined cytokine production by splenic cells in vitro for the elucidation of immunologic mechanisms. Unexpectedly, the liver IL-18 decreased transiently after burn injury, and in vivo IL-18 supplementation improved survival and ameliorated ALI, as well as reducing the lung contents of all cytokines examined, except IL-10. Neutralization of IL-10 cancelled the protective effect of IL-18. In splenic macrophages obtained from burned mice, the production of macrophage inflammatory protein 2 (MIP-2), TNF-alpha, and IL-10 was augmented, whereas in vivo IL-18 supplementation decreased MIP-2 production, but increased IL-10 production. Furthermore, a physiological concentration of IL-18 directly attenuated MIP-2 production by splenic cells in vitro. Burn injury induces LPS hypersensitivity through augmented production of proinflammatory cytokines by systemic macrophages. IL-18 supplementation is protective for LPS-induced lethal ALI through the direct anti-inflammatory effect on macrophages as well as by in vivo acceleration of IL-10 production, and could thus be an effective prophylactic strategy against septic complications in critically ill patients.

Impact of thermal injury on wound infiltration and the dermal inflammatory response

Healing of the burn wound is a critical component of the burn patient's successful recovery. While inflammation is a critical component of the healing process, it is unknown whether the inflammatory response differs between non-burn and burn wounds. To study this, mice were subjected to major burn injury or sham procedure. Wound cells were collected by implantation of polyvinyl alcohol sponges beneath the burn site in injured mice or beneath uninjured skin in sham mice (i.e., non-burn wound). Three days thereafter, skin, wound fluid, and infiltrating cells were collected for analysis. Significant levels of tumor necrosis factor (TNF)-alpha, interleukin (IL-6), monocyte chemoattractant protein (MCP)-1, and keratinocyte-derived chemokine (KC) were observed in burn wound tissue and the wound fluid from both non-burn and burn wounds. Burn injury induced 3-fold higher levels of KC and 50-fold higher levels of IL-6 in the wound fluid compared with non-burn injury. Significant numbers of the cells from both burn and non-burn wounds were CD11b(+), GR1(+), and F4/80(+), suggestive of a myeloid suppressor cell phenotype, whereas CD3(+) T-cells were negligible under both conditions. LPS induced TNF-alpha, IL-6, IL-10, MCP-1, KC, and nitric oxide production in both cell populations, however, IL-6, IL-10, MCP-1, and KC levels were suppressed in burn wound cell cultures. These findings indicate that significant differences in the wound inflammatory response exist between burn and non-burn cutaneous wounds and that the unique characteristics of the inflammatory response at the burn site may be an important contributing factor to post-burn wound healing complications.

Suppression of activation and costimulatory signaling in splenic CD4+ T cells after trauma-hemorrhage reduces T-cell function: a mechanism of post-traumatic immune suppression

Reduced immune function is frequently a consequence of serious injury such as trauma-hemorrhage (T-H). Injury may lead to reduced T-cell activation, resulting in decreased engagement of costimulatory molecules after antigen recognition and in subsequent immunological compromise and anergy. We hypothesized that inhibition of CD28 expression is one possible mechanism by which immune functions are suppressed after T-H. Male C3H/HeN mice (with or without ovalbumin immunization) were subjected to sham operation or T-H and sacrificed after 24 hours. Splenic T cells were then stimulated with concanavalin A or ovalbumin in vivo or in vitro, and CD28, cytotoxic T-lymphocyte antigen 4 (CTLA-4), CD69, and phospho-Akt expression was determined. T-cell proliferation/cytokine production was measured in vitro. Stimulation-induced CD69, CD28, and phospho-Akt up-regulation were significantly impaired after T-H compared with sham-operated animals; however, CTLA-4 expression was significantly higher in the T-H group. Over a 3-day span, stimulated T cells from sham-operated animals showed significantly higher proliferation compared with the T-H group. IL-2 and IFN-gamma were elevated in sham-operated animals, whereas IL-4 and IL-5 rose in the T-H group, revealing a shift from T(H)1 to T(H)2 type cytokine production after T-H. Dysregulation of the T-cell costimulatory pathway is therefore likely to be a significant contributor to post-traumatic immune suppression.

Extracorporeal shock wave therapy suppresses the early proinflammatory immune response to a severe cutaneous burn injury

Following severe burn injury, persistent inflammation perpetuated by surface eschar, bacterial colonisation and neutrophil proteolytic activity can impede normal healing and result in further tissue damage. Extracorporeal shock wave treatment (ESWT) has been shown in the clinical setting to promote the healing of burn and difficult-to-heal wounds; however, the mechanism is unclear. We investigated the role of ESWT on the early proinflammatory response using a severe, full-thickness and highly inflammatory cutaneous burn wound in a murine model. Various wound-healing parameters were measured and leukocyte infiltration quantitated. A panel of 188 candidate genes known to be involved in acute inflammation and wound healing was screened. We show that ESWT of burn wounds 1 hour postwounding significantly blunts polymorphonuclear neutrophil and macrophage infiltration into the wound. ESWT treatment potently attenuates both CC- and CXC-chemokine expression, acute proinflammatory cytokine expression and extracellular matrix proteolytic activity at the wound margin. Given these findings and the clinical success of ESWT, we speculate that ESWT may be a potential therapeutic modality to treat severe wounds wherein excessive inflammatory responses involving increased levels of inflammatory cells, proinflammatory cytokines and proteases may become self-resolving allowing wound healing to progresses by way of normal physiological repair processes.

Differential immunological phenotypes are exhibited after scald and flame burns

A dysfunctional immune system is known to be part of the pathophysiology after burn trauma. However, reports that support this have used a variety of methods, with numerous variables, to induce thermal injury. We hypothesized that, all other parameters being equal, an injury infliction by a scald would yield different immunological responses than one inflicted by a flame. Here, we demonstrated that both burn methods produced a full-thickness burn, yet there was more of an increase in subdermal temperature, hematocrit, mortality, and serum IL-6 concentrations associated with the scald burn. On postinjury day 1, the scald-burned mice showed diminished lymphocyte numbers, interferon gamma production, and lymphocyte T-bet expression as compared with sham- and flame-burned mice. On postburn day 8, spleens from both sets of thermally injured animals showed an increase in proinflammatory myeloid cells as compared with sham-burned mice. Furthermore, the T-cell numbers, T-bet expression, and phenotype were changed such that interferon gamma production was higher in scald-burned mice than in sham- and flame-burned mice. Altogether, the data show that differential immunological phenotypes were observed depending on the thermal injury method used.

Up-regulation of cell surface Toll-like receptors on circulating gammadelta T-cells following burn injury

Burn injury is associated with profound inflammation and activation of the innate immune system involving gammadelta T-cells. Similarly, Toll-like receptors (TLR) are associated with activation of the innate immune response; however, it is unclear whether TLR expression is altered in gammadelta T-cells after major burn injury. To study this, male C57BL/6 mice were subjected to burn injury (25% TBSA) and 1 or 7 days thereafter, blood and spleen cells were isolated and subjected to FACs analysis for TLRs and other phenotypic markers (gammadelta TCR, alphabeta TCR, CD69, CD120b). A marked increase in the number of circulating gammadelta T-cells was observed at 24h post-burn (14% vs. 4%) and a higher percentage of these cells expressed TLR-2. TLR-4 expression was also increased post-burn, but to a lesser degree. These changes in TLR expression were not associated with altered CD69 or CD120b expression in gammadelta T-cells. The mobilization of, and increased TLR expression in, gammadelta T-cells was transient, as phenotypic changes were not evident at 7 days post-burn or in gammadelta T-cells from the circulation or spleen. The increases in TLR expression were not observed in alphabeta T-cells after burn injury. In conclusion, 24h after burn injury mobilization of gammadelta T-cells with increased TLR expression was observed. This finding suggests that this unique T-cell population is critical in the innate immune response to injury, possibly through the recognition of danger signals by TLRs.

Burn injury-induced alterations in wound inflammation and healing are associated with suppressed hypoxia inducible factor-1alpha expression

A major complication associated with burn injury is delayed wound healing. While healing of the burn injury site is essential, healing of distal injury sites caused by surgical interventions and other processes also is important. The impact of burn injury on healing of these distal wound sites is not understood clearly. To study this, mice were subjected to major burn injury or a sham procedure. Immediately following, excisional wounds were made on the dorsal surface caudal to the burn site and wound closure was monitored over a 7-d period by planimetry. In a second series of experiments, plasma and excisional wounds were collected for in vitro analysis of cyto- and chemokine levels, L-arginine metabolism, and hypoxia-inducible factor (HIF)-1alpha expression. At 1-7 d post-injury, a significant inflammatory response was evident in both groups, but the healing process was delayed in the burn-injured mice. At 3 d post-injury, wound levels of tumor necrosis factor-alpha (TNF-alpha), interleukin-6 (IL-6), and keratinocyte-derived chemokine were suppressed in the burn group. This difference in the wound inflammatory response was independent of changes in L-arginine metabolism (nitrate levels, inducible nitric oxide synthase expression, arginase activity), but correlated with a marked reduction in HIF-1alpha protein levels. In conclusion, these findings suggest that HIF-1alpha and the inflammatory response play a significant role in wound healing, and reduced levels of HIF-1alpha contribute to the impaired healing response post-burn.

Prophylactic treatment with fms-like tyrosine kinase-3 ligand after burn injury enhances global immune responses to infection

Severely burned patients are susceptible to infections with opportunistic organisms due to altered immune responses and frequent wound contamination. Immunomodulation to enhance systemic and local responses to wound infections may be protective after burn injury. We previously demonstrated that pretreatments with fms-like tyrosine kinase-3 (Flt3) ligand (Flt3L), a dendritic cell growth factor, increase the resistance of mice to a subsequent burn injury and wound infection by a dendritic cell-dependent mechanism. This study was designed to test the hypothesis that Flt3L administration after burn injury decreases susceptibility to wound infections by enhancing global immune cell activation. Mice were treated with Flt3L after burn injury and examined for survival, wound and systemic bacterial clearance, and immune cell activation after wound inoculation with Pseudomonas aeruginosa. To gain insight into the local effects of Flt3L at the burn wound, localization of Langerhans cells was examined. Mice treated with Flt3L had significantly greater numbers of CD25-expressing T cells and CD69-expressing T and B cells, neutrophils, and macrophages after, but not before, infection. Overall leukocyte apoptosis in response to infection was decreased with Flt3L treatment. Survival and local and systemic bacterial clearance were enhanced by Flt3L. Langerhans cells appeared in the dermis of skin bordering the burn wound, and further increased in response to wound infection. Flt3L augmented the appearance of Langerhans cells in response to both injury and infection. These data suggest that dendritic cell enhancement by Flt3L treatments after burn injury protects against opportunistic infections through promotion of local and systemic immune responses to infection.

Thermal injury elevates the inflammatory monocyte subpopulation in multiple compartments

Recent publications have demonstrated that human resident and inflammatory monocyte (IM) subpopulations have equivalents in rodents. The effect of thermal injury upon these subpopulations has not been studied. Mice were given a scald burn and killed on postburn days (PBDs) 2, 4, and 8. Bone marrow, blood, and spleen white cells were isolated, and the percentage of resident monocytes (CD11b LY6C), IMs (CD11b LY6C), and monocyte progenitors (macrophage-colony-forming unit [M-CFU]) were determined. The ability of each monocyte population to make TNF-alpha was determined by intracellular cytokine staining. Finally, the ability of sorted fractions from PBD 8 spleen to inhibit lymphocyte proliferation was performed. We noted that there was an increase in M-CFU in the blood and spleen at PBD 8, but the marrow only had a nonsignificant increase in M-CFU. All compartments showed a significant increase in the number of IMs by PBD 8, but no significant changes in resident monocytes were seen. In all compartments, IMs were a major source of TNF-alpha. The postburn increase in IMs and monocyte progenitors in the spleen was accompanied by an increase in the monocyte chemokine monocyte chemoattractant protein 1 and constitutively high levels of the progenitor chemokine stromal-derived factor 1alpha. After burn injury, mice deficient in the receptor for soluble TNF-alpha had equal levels of splenic M-CFU and monocytes, as did wild-type mice, suggesting that this cytokine is not essential for this effect. We conclude that in this model, IMs are a significant source of in vivo TNF-alpha.

Acute alcohol intoxication potentiates neutrophil-mediated intestinal tissue damage after burn injury

This study examined whether acute alcohol (EtOH) intoxication before burn injury potentiates postburn intestinal tissue damage and whether neutrophils have any role in the damage under those conditions. Male rats ( approximately 250 g) were gavaged with EtOH to achieve a blood EtOH level of approximately 100 mg/dL or with saline and received either approximately 12.5% or approximately 25% total body surface area (TBSA) burn or sham injury. Rats were killed at 4 or 24 h after injury, and various parameters were measured. As compared with sham animals, burn injury alone (regardless of size) resulted in a significant increase in intestinal tissue myeloperoxidase (MPO; an index of neutrophil infiltration) activity and IL-18 levels 4 h after injury. Furthermore, rats receiving 25% TBSA, but not 12.5%, burn exhibited intestine edema. The IL-18 and MPO activity were normalized at 24 h after injury in rats receiving 12.5% TBSA burn, whereas these parameters remained elevated at 24 h in rats with 25% burn. The presence of EtOH in rats at the time of burn injury exacerbated the levels of IL-18, MPO activity, and edema at 4 and 24 h after burn injury. Treatment of rats with anti-IL-18 antibodies or with antineutrophil antiserum prevented the increase in the above parameters after EtOH and burn injury, except that the depletion of neutrophils did not prevent the IL-18 increase. In summary, these findings suggest that acute EtOH intoxication exacerbates postburn intestinal tissue damage after burn injury, and that it is, in part, neutrophil mediated.

Inhibition of protein tyrosine phosphatases prevents mesenteric lymph node T-cell suppression following alcohol intoxication and burn injury

Previously, we have shown that acute alcohol (EtOH) intoxication before burn injury potentiates the suppression of mesenteric lymph node T-cell effector responses. Moreover, the suppression in T-cell was accompanied with a decrease in p-38 and extracellular-signal-regulated kinase (ERK) activation. This study examined the role of protein tyrosine phosphatases (PTP) in suppressed T-cell p-38, ERK, and cytokine production after EtOH intoxication and burn injury. A blood EtOH level of approximately 100 mg/dl in male rats (approximately 250 g) was achieved by gavaging animals with 5 ml of 20% EtOH suspension 4 hours before burn or sham injury (approximately 12.5% or 25% total body surface area [TBSA]). One day after injury, rats were killed and mesenteric lymph node T-cell cytokine (IL-2/IFN-gamma) production, p-38, and ERK activation were measured. As compared with shams, there was a significant decrease in T-cell cytokine production after 25% and not 12.5% TBSA burn injury. However, T-cell IL-2/IFN-gamma levels were significantly decreased in rats receiving a combined insult of EtOH and burn injury regardless of the percentage of burn area. Furthermore, we found a significant decrease in p-38 and ERK-1/2 phosphorylation in T-cells of rats receiving a combined insult of EtOH and 12.5% TBSA burn compared with shams. Treatment of cells with PTP inhibitor pervanadate (10 muM) prevented T-cell p-38/ERK suppression. The suppression in IL-2/IFN-gamma production was also attenuated in T-cells cultured in the presence of pervanadate. These findings suggest that an increase in PTP activity may contribute to T-cell suppression after EtOH intoxication and burn injury.

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.

Long-term immunosuppression in burned patients assessed by in vitro neutrophil oxidative burst (Phagoburst®)

OBJECTIVE

To assess the duration and magnitude of immunosuppression induced by burns as measured by the neutrophil oxidative burst in vitro.

DESIGN

Prospective exploratory cohort study.

SETTING

Tertiary referral unit, University Hospital, Linkoping, Sweden (National Burn Unit). PATIENTS AND HEALTHY VOLUNTEERS (CONTROLS): Twenty-eight subjects consecutively admitted to the Burn Unit. The mean total burn surface area (TBSA%) was 36 (range 13-87) and mean age 44 years (range 14-89). Patients' data were collected prospectively in the burn unit, which also included sequential organ failure assessment (SOFA) score.

INTERVENTIONS

None.

MEASUREMENTS AND RESULTS

To assess the changes in the oxidative capacity of neutrophils after the burn, blood samples for the Phagoburst analysis were taken on admission and at least once every second week for the duration of stay in hospital and thereafter monthly up to 12 months after the burn. Neutrophils were stimulated in vitro by Escherichia coli, phorbol 12-phorbol myristate 13-acetate (PMA), and peptide N-formyl-Met-Leu-Phe (fMLP). Oxidative burst was measured by flow cytometry. Oxidative capacity of the neutrophils decreased similarly for all three stimulants: there was a pathological decrease shortly after admission, with the lowest value occurring between days 7 and 10, followed by a gradual recovery during the ensuing months. Full recovery (to the values of the controls) was seen first 3.5 months after the burn. Using multiple regression, we found that only age and time since the burn significantly (p<0.05) affected the oxidative burst. White cell count (WCC) and C-reactive protein (CRP) values returned to reference ranges long before the oxidative burst.

CONCLUSIONS

This study provides evidence that immunosuppression in those injured by burns, as assessed by the in vitro oxidative burst of neutrophils, remains long after the event of the burn (up to 3.5 months after burn). Absence of correlations to TBSA%, FTB%, blood transfusion, opiates provided, and multiple organ failure score and laboratory infection variables together with the finding that decreased oxidative burst was uniform after the injury, suggesting that this immunosuppression is primarily due to the general metabolic response rather than recurring infections.

Postburn monocytes are the major producers of TNF-alpha in the heterogeneous splenic macrophage population

Increased tumor necrosis factor (TNF)-alpha production by postburn splenic macrophages is well documented. Splenic macrophages are a heterogeneous population, and the effect of thermal injury on these subpopulations has not been documented. We examined the effects of scald injury on myeloid cells with the phenotype of red pulp, white pulp, and marginal zone monocyte/macrophages. We found that thermal injury greatly increased the number of splenocytes with the phenotype of white pulp monocytes. These cells were the major producers of TNF-alpha in the postburn spleen. Cells with the red pulp macrophage phenotype had an increased ability to make TNF-alpha after burn injury, but had only half the capacity to make TNF-alpha as did postburn monocytes. The postburn changes in TNF-alpha production correlated with an increased in vivo susceptibility to endotoxin. The increase in monocytes in the spleen from postburn days 1 to 10 correlated with an increasing ability of splenocytes to produce granulocyte colony-stimulating factor, monocyte chemoattractant protein 1, macrophage inflammatory protein 2, and macrophage inflammatory protein 1-alpha. These data suggest that the monocyte is a major source of inflammatory cytokines in the postburn spleen.

Acute alcohol intoxication increases interleukin-18-mediated neutrophil infiltration and lung inflammation following burn injury in rats

In this study, we examined whether IL-18 plays a role in lung inflammation following alcohol (EtOH) and burn injury. Male rats (∼250 g) were gavaged with EtOH to achieve a blood EtOH level of ∼100 mg/dl before burn or sham injury (∼12.5% total body surface area). Immediately after injury, rats were treated with vehicle, caspase-1 inhibitor AC-YVAD-CHO to block IL-18 production or with IL-18 neutralizing anti-IL-18 antibodies. In another group, rats were treated with anti-neutrophil antiserum ∼16 h before injury to deplete neutrophils. On day 1 after injury, lung tissue IL-18, neutrophil chemokines (CINC-1/CINC-3), ICAM-1, neutrophil infiltration, MPO activity, and water content (i.e., edema) were significantly increased in rats receiving a combined insult of EtOH and burn injury compared with rats receiving either EtOH intoxication or burn injury alone. Treatment of rats with caspase-1 inhibitor prevented the increase in lung tissue IL-18, CINC-1, CINC-3, ICAM-1, MPO activity, and edema following EtOH and burn injury. The increase in lung IL-18, MPO, and edema was also prevented in rats treated with anti-IL-18 antibodies. Furthermore, administration of anti-neutrophil antiserum also attenuated the increase in lung MPO activity and edema, but did not prevent the increase in IL-18 levels following EtOH and burn injury. These findings suggest that acute EtOH intoxication before burn injury upregulates IL-18, which in turn contributes to increased neutrophil infiltration. Furthermore, the presence of neutrophils appears to be critical for IL-18-meditaed increased lung tissue edema following a combined insult of EtOH and burn injury.

Effect of Transforming Growth Factor-β Neutralization on Survival and Bacterial Clearance in a Murine Model of Pseudomonas aeruginosa Burn Wound Infection

Transforming growth factor-beta (TGF-beta), a cytokine with anti-inflammatory properties, may contribute to postburn immunosuppression. This study was designed to determine whether neutralizing TGF-beta in burned mice could improve resistance to infection. C57BL/6J mice received a 35% TBSA flame burn under isoflurane anesthesia. Four days after injury, mice were treated with TGF-beta antibody or nonspecific IgG. On day 5 after burn injury, mice were inoculated with Pseudomonas aeruginosa at the burn wound site or received intraperitoneal injection with P. aeruginosa. Mice treated with anti-TGF-beta exhibited significantly improved survival compared with mice treated with nonspecific IgG after challenge with P. aeruginosa at the burn wound site or after intraperitoneal injection of P. aeruginosa. In mice with burn wound infections, bacterial counts in burn wounds, blood, and lung were decreased in mice treated with anti-TGF-beta compared with mice treated with control IgG. Bacterial counts in lung and blood after intraperitoneal challenge with P. aeruginosa also were significantly lower in burned mice treated with anti-TGF-beta compared with those treated with nonspecific IgG. Our data suggest that neutralization of TGF-beta at 4 days after burn injury in mice improves local and systemic clearance of P. aeruginosa and enhances survival after P. aeruginosa challenge.

T cells of the gammadelta T-cell receptor lineage play an important role in the postburn wound healing process

Although gammadelta T cells have been implicated in various aspects of the dermal wound healing process, their role in postburn wound healing processes has not been investigated. To study this, we subjected mice deficient in gammadelta T cells (ie, T-cell receptor delta gene [delta TCR]) and wild-type (WT; C57BL6J) mice to burn injury (25% TBSA) or sham treatment; skin samples were isolated 3 days later. Marked inflammation of the injury site was observed in WT mice but was markedly reduced in delta TCR mice. Postinjury fibroblast growth factor, platelet-derived growth factor granulocyte-colony stimulating factor levels, and nitrite/nitrate were elevated in skin samples from injured WT mice, whereas skin tissue levels of these growth factors and inflammatory mediators was significantly atteunuated in delta TCRmice. In conclusion, these findings support the concept that gammadelta T cells are important to postburn wound healing via the production of growth factors and, potentially, regulation of inducible nitric oxide synthase activation.

Effect of blood transfusion on outcome after major burn injury: a multicenter study

OBJECTIVE

To delineate blood transfusion practices and outcomes in patients with major burn injury.

CONTEXT

Patients with major burn injury frequently require multiple blood transfusions; however, the effect of blood transfusion after major burn injury has had limited study.

DESIGN

Multicenter retrospective cohort analysis.

SETTING

Regional burn centers throughout the United States and Canada.

PATIENT POPULATION

Patients admitted to a participating burn center from January 1 through December 31, 2002, with acute burn injuries of >or=20% total body surface area.

OUTCOMES MEASURED

Outcome measurements included mortality, number of infections, length of stay, units of blood transfused in and out of the operating room, number of operations, and anticoagulant use.

RESULTS

A total of 21 burn centers contributed data on 666 patients; 79% of patients survived and received a mean of 14 units of packed red blood cells during their hospitalization. Mortality was related to patient age, total body surface area burn, inhalation injury, number of units of blood transfused outside the operating room, and total number of transfusions. The number of infections per patient increased with each unit of blood transfused (odds ratio, 1.13; p<.001). Patients on anticoagulation during hospitalization received more blood than patients not on anticoagulation (16.3+/-1.5 vs. 12.3+/-1.5, p<.001).

CONCLUSIONS

The number of transfusions received was associated with mortality and infectious episodes in patients with major burns even after factoring for indices of burn severity. The utilization of blood products in the treatment of major burn injury should be reserved for patients with a demonstrated physiologic need.

Polarized Th2 cytokine production in patients with hypertrophic scar following thermal injury

Following thermal injury, hypertrophic scar (HSc) is a frequent and severe form of fibrosis of the skin, which limits movement and compromises the cosmetic appearance and function of the skin. Prolonged pruritus and dysesthesia are also common problems in the previously injured, fibrotic tissues, as current understanding of the pathogenesis is limited, and few effective therapies exist, as with other fibroproliferative disorders (FPD). To investigate the role of T cells and their cytokines in the development of HSc, intracellular cytokine synthesis of circulating T cells was measured serially in burn patients using flow cytometry from the time of injury to over a 1-year period during which many patients developed HSc. Within 1 month of injury, low interferon-gamma (IFN-gamma)-positive T cells (Th1) were found in association with low interleukin-12 (IL-12) and absent IFN-gamma cytokine levels in the serum. IL-4-positive Th 2 cells, however, were significantly increased compared with normal controls by 2 months postinjury. In burn patients with HSc, serum IL-10 and transforming growth factor-beta (TGF-beta) levels were also significantly increased early after burn injury in patients who later developed HSc compared with normal volunteers and with a subset of burn patients who did not develop HSc, before returning to normal levels after 6 months. Activated peripheral blood mononuclear cells (PBMC) demonstrated that mRNA for IFN-gamma was present only in normal volunteers or patients without HSc but was undetectable in HSc patients. IL-4 mRNA levels were increased in the PBMCs of burn patients with HSc. In HSc tissues, IL-4 mRNA was increased, whereas, IFN-gamma mRNA was reduced compared with normal skin and mature scar. Increased CD3(+) and CD4(+) cells were present in HSc tissues compared with normal skin and were coexpressed with the fibrogenic cytokine TGF-beta. These longitudinal studies in human patients with HSc suggest that fibrosis in the skin is associated with a polarized Th2 systemic response to injury that leads to increased T cells and their Th2 fibrogenic cytokines in tissues and the development of fibrosis and HSc.

Simultaneous aberrations in MØ and T cell function adversely affect trauma patients' clinical outcome: A possible faulty IL-13 feedback loop

Possible defective trauma patients' Mphi-T-cell feedback interactions between T cell IL-13 production and IL-1beta and IL-18 Mphi secretion were assessed. Mphi produced IL-1 and IL-18 augment T cell IL-13, which in turn limits excessive macrophage activation. Immunodepressed patients' T cells (depressed proliferation to alphaCD3 + alphaCD4) had decreased IL-13 production concomitant to aberrant Mphi activities ( upward arrow mTNFalpha, downward arrow IL-10) and consequent multiple organ failure (MOF). Decreased IL-13 levels in patients' T cell and diminished Mphi supernatant augmentation of healthy controls' T cell IL-13 production appeared concomitantly, suggesting patients' aberrant monokine levels might intensify in vivo T cell dysfunction severity. Patients' Mphi supernatants, which failed to augment controls' T cell IL-13 production, had depressed IL-1beta and lower induction of IL-18 than immunocompetent patients' Mphi, but combined addition of IL-1beta and IL-18 restored these Mphis' IL-13 enhancing activity. These data suggest that immunodepressed patients' aberrant monokine and depressed T cell IL-13 production are independent but synergistic contributors to emergence of MOF.

Nitric oxide contributes to the development of a post-injury Th2 T-cell phenotype and immune dysfunction

Severe injury induces immune dysfunction resulting in increased susceptibility to opportunistic infections. Previous studies from our laboratory have demonstrated that post-burn immunosuppression is mediated by nitric oxide (NO) due to the increased expression of macrophage inducible nitric oxide synthase (iNOS). In contrast, others suggest that injury causes a phenotypic imbalance in the regulation of Th1- and Th2 immune responses. It is unclear whether or not these apparently divergent mediators of immunosuppression are interrelated. To study this, C57BL/6 mice were subjected to major burn injury and splenocytes were isolated 7 days later and stimulated with antiCD3. Burn injury induced NO-mediated suppression of proliferative responses that was reversed in the presence of the NOS inhibitor L-monomethyl-L-arginine and subsequently mimicked by the addition of the NO donor, S-nitroso-N-acetyl-penicillamine (SNAP). SNAP also dose-dependently suppressed IFN-gamma and IL-2 (Th1), but not IL-4 and IL-10 (Th2) production. Delaying the addition of SNAP to the cultures by 24 h prevented the suppression of IFN-gamma production. The Th2 shift in immune phenotype was independent of cGMP and apoptosis. The addition of SNAP to cell cultures also induced apoptosis, attenuated mitochondrial oxidative metabolism and induced mitochondrial membrane depolarization. However, these detrimental cellular effects of NO were observed only at supra-physiologic concentrations (>250 microM). In conclusion, these findings support the concept that NO induces suppression of cell-mediated immune responses by selective action on Th1 T cells, thereby promoting a Th2 response.

Opiate Analgesics Contribute to the Development of Post-Injury Immunosuppression1

BACKGROUND

Immune dysfunction and post-injury infections are complications associated with thermal injury. Opiates, the analgesic of choice for the treatment of post-burn pain, can also induce similar immune complications. However, the impact of therapeutic opiates on post-burn immune dysfunction is unknown.

MATERIALS AND METHODS

C57BL/6 mice were subjected to a small 6.25% total body surface area (TBSA) burn or sham procedure. The mice were left untreated or treated with morphine sulfate by subcutaneous implantation of an Alzet pump that administered morphine sulfate at a rate of 2 mg/kg body weight/day. Plasma, splenocytes and splenic macrophages were isolated for in vitro analysis 1, 4, or 7 days later.

RESULTS

Neither burn injury nor morphine treatment alone significantly altered splenic T-cell proliferation at 1, 4, or 7 days post-injury/treatment. In contrast, morphine treatment of injured mice suppressed splenic T-cell proliferation at 4 and 7 days post-injury/treatment. The suppressed proliferation of T-cells correlated with increased levels of the nitric oxide and an immunosuppressive Th-2 type phenotype. In contrast morphine treatment did not accentuate the suppressed T-cell proliferative responses associated with larger injuries covering 12.5% and 25% TBSA. Splenic macrophage function was unaffected with the exception that LPS-induced nitric oxide production was elevated in the injured mice treated with morphine.

CONCLUSIONS

These findings demonstrate that those mice treated with a clinically relevant dose of morphine sulfate after an "immunologically insignificant" burn displayed immunosuppression and a Th-2 cytokine profile. Thus, the therapeutic administration of exogenous opiates appears to contribute to the development of post-burn immune dysfunction.

The role of NO in macrophage dysfunction at early stage after burn injury

AIM

To explore the role of nitric oxide (NO) in macrophage dysfunction at early stage after burn injury.

METHOD

Peritoneal macrophages were isolated and cultured from early stage burnt mice. NO production and inducible NO synthase (iNOS) expression in the macrophages were checked by the Greiss method and real-time PCR (TaqMan), respectively. l-Arginine, the substrate of NO producing, or N-monomethyl-l-arginine (l-NMMA), a competing blocker of NOS was administered to the culture, the changes of NO, TNF-alpha and PGE2 productions were measured, additionally the changes of the iNOS, TNF-alpha and COX-2 expression were assayed by real-time PCR. After that, the effects of l-arginine and l-NMMA were determined on burnt macrophage influencing the proliferation of normal splenic lymphocytes.

RESULT

A large amount of NO was produced by macrophages from post burn hour 6 (6PBH) with a high level of iNOS expression. l-Arginine could increase NO production in a dosage-dependent manner, while l-NMMA attenuated NO production, but neither could affect iNOS expression. Moreover, l-arginine enhanced productions of both the latter produced TNF-alpha and PGE2 from burnt macrophages, and the expressions of TNF-alpha and COX-2 were improved significantly, while l-NMMA did reverse ways. It was found that macrophages from post burn hour 24 mice could inhibit Con A-stimulated normal splenic lymphocytes dramatically, l-NMMA could decrease this function significantly, but l-arginine could not influence the suppression.

CONCLUSION

Our experiment indicated NO derived from burnt macrophage played a vital role in macrophage producing excessive TNF-alpha and PGE2, and suppressing lymphocyte function at early stage after burn injury.

Is antibody therapy of tumor compromised by infusion-related reactions?

Evidence suggests that amelioration of childhood immune thrombocytopenic purpura and some other autoimmune states by intravenous normal IgG is due to the following chain of events: (1) cross-linking of Fcgamma-receptors on blood effector cells; (2) release of mediators from these cells, often yielding an infusion-related reaction; (3) mediator-induced development of a cytokine field characterized by a mutually stabilizing Th2 polarization of CD4 T lymphocytes and alternative activation of macrophages; (4) selective quiescence of these macrophages towards targets coated with IgG autoantibody, due to increased expression of the macrophage Fcgamma-receptor IIB. In this paper it is postulated that in the field of antibody therapy of tumor, an undesirable delayed or absent subsidence of antibody-coated tumor is due to immunomodulation of the same type as yields amelioration of autoimmunity, and arising from a similar chain of events. If the postulate is correct the chain could usefully be broken at the level of mediator action, possibly by blocking that increased synthesis of prostaglandin E(2) which is catalyzed by the enzyme cyclooxygenase-2.

Expression of Toll-like receptors 2 and 4 is downregulated after operation

BACKGROUND

Toll-like receptors (TLR) that recognize microbial pathogens play a critical role in innate immunity; however, their expression and function after surgery remain unknown. The aim of this study was to examine TLR2 and TLR4 expression on monocytes and their responses to each agonist after surgical insults.

METHODS

Blood samples were obtained from 83 patients who underwent gastrointestinal surgery. TLR2, TLR4, and inducible nitric oxide synthase expressions on peripheral blood mononuclear cells (PBMCs) were analyzed by flow cytometry. Macrophage-activating lipopeptide-2 or lipopolysaccharide-induced tumor necrosis factor-alpha and interleukin-6 production was measured by enzyme-linked immunosorbent assay.

RESULTS

TLR2 and TLR4 decreased and showed the lowest values on the postoperative days 3 and 1, respectively. Macrophage-activating lipopeptide-2-stimulated tumor necrosis factor-alpha and interleukin-6 production was decreased immediately after the operation (P<.05), increased to a maximum value on postoperative day 1, and then decreased gradually. Lipopolysaccharide-stimulated tumor necrosis factor-alpha production was also suppressed immediately (P<.05) after operation then showed a gradual increase to maximum values on postoperative day 3. Inducible nitric oxide synthase in cultured PBMC that was obtained immediately after operation was upregulated (P<.05).

CONCLUSION

Expressions of TLR2 and TLR4 were downregulated by operation, and agonist-induced cytokine production was suppressed transiently and soon increased through the activation of PBMC. The present study may offer new insights for postoperative modulation of innate immunity under surgical stress.