Burn injury induces a change in T cell homeostasis affecting preferentially CD4+T cells

Tracing the evolving dynamics and research hotspots of microbiota and immune microenvironment from the past to the new era

Gut microbiota can regulate many physiological processes within gastrointestinal tract and other distal sites. Dysbiosis may not only influence chronic diseases like the inflammatory bowel disease (IBD), metabolic disease, tumor and its therapeutic efficacy, but also deteriorate acute injuries. This article aims to review the documents in this field and summarize the research hotspots as well as developing processes. Gut microbiota and immune microenvironment-related documents from 1976 to 2022 were obtained from the Web of Science Core Collection database. Bibliometrics was used to assess the core authors and journals, most contributive countries and affiliations together with hotspots in this field and keyword co-occurrence analysis. Data were visualized to help comprehension. Nine hundred and twelve documents about gut microbiota and immune microenvironment were retrieved, and the annual publications increased gradually. The most productive author, country, and affiliation were "Zitvogel L," USA and "UNIV TEXAS MD ANDERSON CANC CTR," respectively. FRONTIERS IN IMMUNOLOGY, CANCERS, and INTERNATIONAL JOURNAL OF MOLECULAR SCIENCE were the periodicals with most publications. Keyword co-occurrence analysis identified three clusters, including gut microbiota, inflammation, and IBD. Combined with the visualized analysis of documents and keyword co-occurrence as well as literature reading, we recognized three key topics of gut microbiota: cancer and therapy; immunity, inflammation and IBD; acute injuries and metabolic diseases. This article revealed researches on gut microbiota and immune microenvironment were growing. More attention should be given to the latest hotspots like gut microbiota, inflammation, IBD, cancer and immunotherapy, acute traumas, and metabolic diseases.IMPORTANCEGut microbiota can regulate many physiological processes within gastrointestinal tract and other distal sites. Dysbiosis may not only influence chronic diseases like inflammatory bowel disease (IBD), metabolic disease, tumor and its therapeutic efficacy, but also deteriorate acute injuries. While the application of bibliometrics in the field of gut microbiota and immune microenvironment still remains blank, which focused more on the regulation of the gut microbiota on the immune microenvironment of different kinds of diseases. Here, we intended to review and summarize the presented documents in gut microbiota and immune microenvironment field by bibliometrics. And we revealed researches on gut microbiota and immune microenvironment were growing. More attention should be given to the latest hotspots like gut microbiota, inflammation, IBD, cancer and immunotherapy, acute traumas, and metabolic diseases.

A burns and COVID-19 shared stress responding gene network deciphers CD1C-CD141- DCs as the key cellular components in septic prognosis

Differential body responses to various stresses, infectious or noninfectious, govern clinical outcomes ranging from asymptoma to death. However, the common molecular and cellular nature of the stress responsome across different stimuli is not described. In this study, we compared the expression behaviors between burns and COVID-19 infection by choosing the transcriptome of peripheral blood from related patients as the analytic target since the blood cells reflect the systemic landscape of immune status. To this end, we identified an immune co-stimulator (CD86)-centered network, named stress-response core (SRC), which was robustly co-expressed in burns and COVID-19. The enhancement of SRC genes (SRCs) expression indicated favorable prognosis and less severity in both conditions. An independent whole blood single-cell RNA sequencing of COVID-19 patients demonstrated that the monocyte-dendritic cell (Mono-DC) wing was the major cellular source of SRC, among which the higher expression of the SRCs in the monocyte was associated with the asymptomatic COVID-19 patients, while the quantity-restricted and function-defected CD1C-CD141-DCs were recognized as the key signature which linked to bad consequences. Specifically, the proportion of the CD1C-CD141-DCs and their SRCs expression were step-wise reduced along with worse clinic conditions while the subcluster of CD1C-CD141-DCs from the critical COVID-19 patients was characterized of IFN signaling quiescence, high mitochondrial metabolism and immune-communication inactivation. Thus, our study identified an expression-synchronized and function-focused gene network in Mono-DC population whose expression status was prognosis-related and might serve as a new target of diagnosis and therapy.

Researches on cognitive sequelae of burn injury: Current status and advances

Burn injury is a devastating disease with high incidence of disability and mortality. The cognitive dysfunctions, such as memory defect, are the main neurological sequelae influencing the life quality of burn-injured patients. The post-burn cognitive dysfunctions are related to the primary peripheral factors and the secondary cerebral inflammation, resulting in the destruction of blood-brain barrier (BBB), as is shown on Computed Tomography (CT) and magnetic resonance imaging examinations. As part of the neurovascular unit, BBB is vital to the nutrition and homeostasis of the central nervous system (CNS) and undergoes myriad alterations after burn injury, causing post-burn cognitive defects. The diagnosis and treatment of cognitive dysfunctions as burn injury sequelae are of great importance. In this review, we address the major manifestations and interventions of post-burn cognitive defects, as well as the mechanisms involved in memory defect, including neuroinflammation, destruction of BBB, and hormone imbalance.

Exendin-4 Exacerbates Burn-Induced Mortality in Mice by Switching to Th2 Response

INTRODUCTION

To determine if Exendin-4 could be a therapeutic agent for burn-induced hyperglycemia.

MATERIALS AND METHODS

Male Balb/c mice received a bolus of Exendin-4 intraperitoneally immediately after 15% total body surface area scald injury. Tail glucose levels were recorded and T-cell functions were analyzed at 4 h and 24 h postburn (pb). Pancreatic pathology was observed consecutively. The secretions of cytokines were detected in serum, spleen, and lung. Apoptosis of splenic CD3+ T-cells was examined by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling and flow cytometry.

RESULTS

Although Exendin-4 could attenuate burn-induced hyperglycemia in mice at 4 h pb, it accelerated their survival dose dependently with progressive depletion of splenocyte number. T-cell function underwent two-phasic changes following Exendin-4 treatment. Compared to placebo mice, T-cell from Exendin-4-treated mice was manifested with increased proliferation, while decreased IL-2 secretion and lower ratio of IL-4/IFN-γ at 4 h pb. However, at 24 h pb, it showed decreased proliferation, while increased IL-2 secretion and higher ratio of IL-4/IFN-γ. Exendin-4 could elicit higher circulating IL-6 and IL-10 levels at 4 h pb, which were pronounced in the lung at 24 h pb. In the meanwhile, severe inflammation could be found in the pancreas. At 24 h pb, the numbers of terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling or caspase-3 positive cells and the apoptosis of CD3+ T-cells were significantly increased in the spleens of Exendin-4 mice relative to placebo mice.

CONCLUSIONS

These data support a pathogenic role of Exendin-4 signaling during thermal injury, warning against its clinical application in acute insults.

sEH-derived metabolites of linoleic acid drive pathologic inflammation while impairing key innate immune cell function in burn injury

Oxylipins alter immune cell function and potentially drive pathophysiology in burn and sepsis patients. Past and recent data reveal a correlation between increased systemic EpOME levels and reduced survival in human burn trauma and sepsis. This work extends these studies and provides evidence that the downstream sEH-derived metabolites, DiHOMEs, are driving worsening outcomes by altering the immune response. Inhibiting DiHOME metabolite formation with the sEH inhibitor, 1-trifluoromethoxyphenyl-3-(1-propionylpiperidin-4-yl) urea (TPPU), restored immune function by increasing immune cell survival and function. These data support the hypothesis that sEH-derived linoleic acid diols are responsible for increased mortality in burn and sepsis patients and also provide a rationale for testing the therapeutic blockage of DiHOME generation in burn and sepsis patients to improve their outcomes.

Fatty acid composition in the Western diet has shifted from saturated to polyunsaturated fatty acids (PUFAs), and specifically to linoleic acid (LA, 18:2), which has gradually increased in the diet over the past 50 y to become the most abundant dietary fatty acid in human adipose tissue. PUFA-derived oxylipins regulate a variety of biological functions. The cytochrome P450 (CYP450)–formed epoxy fatty acid metabolites of LA (EpOMEs) are hydrolyzed by the soluble epoxide hydrolase enzyme (sEH) to dihydroxyoctadecenoic acids (DiHOMEs). DiHOMEs are considered cardioprotective at low concentrations but at higher levels have been implicated as vascular permeability and cytotoxic agents and are associated with acute respiratory distress syndrome in severe COVID-19 patients. High EpOME levels have also correlated with sepsis-related fatalities; however, those studies failed to monitor DiHOME levels. Considering the overlap of burn pathophysiology with these pathologies, the role of DiHOMEs in the immune response to burn injury was investigated. 12,13-DiHOME was found to facilitate the maturation and activation of stimulated neutrophils, while impeding monocyte and macrophage functionality and cytokine generation. In addition, DiHOME serum concentrations were significantly elevated in burn-injured mice and these increases were ablated by administration of 1-trifluoromethoxyphenyl-3-(1-propionylpiperidin-4-yl) urea (TPPU), a sEH inhibitor. TPPU also reduced necrosis of innate and adaptive immune cells in burned mice, in a dose-dependent manner. The findings suggest DiHOMEs are a key driver of immune cell dysfunction in severe burn injury through hyperinflammatory neutrophilic and impaired monocytic actions, and inhibition of sEH might be a promising therapeutic strategy to mitigate deleterious outcomes in burn patients.

Identifying changes in immune cells and constructing prognostic models using immune-related genes in post-burn immunosuppression

BACKGROUND

Burn patients are prone to infection as well as immunosuppression, which is a significant cause of death. Currently, there is a lack of prognostic biomarkers for immunosuppression in burn patients. This study was conducted to identify immune-related genes that are prognosis biomarkers in post-burn immunosuppression and potential targets for immunotherapy.

METHODS

We downloaded the gene expression profiles and clinical data of 213 burn patients and 79 healthy samples from the Gene Expression Omnibus (GEO) database. Immune infiltration analysis was used to identify the proportion of circulating immune cells. Functional enrichment analyses were carried out to identify immune-related genes that were used to build miRNA-mRNA networks to screen key genes. Next, we carried out correlation analysis between immune cells and key genes that were then used to construct logistic regression models in GSE77791 and were validated in GSE19743. Finally, we determined the expression of key genes in burn patients using quantitative reverse transcription polymerase chain reaction (qRT-PCR).

RESULTS

A total of 745 differently expressed genes were screened out: 299 were up-regulated and 446 were down-regulated. The number of Th-cells (CD4+) decreased while neutrophils increased in burn patients. The enrichment analysis showed that down-regulated genes were enriched in the T-cell activation pathway, while up-regulated genes were enriched in neutrophil activation response in burn patients. We screened out key genes (NFATC2, RORA, and CAMK4) that could be regulated by miRNA. The expression of key genes was related to the proportion of Th-cells (CD4+) and survival, and was an excellent predictor of prognosis in burns with an area under the curve (AUC) value of 0.945. Finally, we determined that NFATC2, RORA, and CAMK4 were down-regulated in burn patients.

CONCLUSION

We found that NFATC2, RORA, and CAMK4 were likely prognostic biomarkers in post-burn immunosuppression and potential immunotherapeutic targets to convert Th-cell dysfunction.

Gut Microbial Changes and their Contribution to Post-Burn Pathology

ABSTRACT

Burn injuries are a common form of traumatic injury that leads to significant morbidity and mortality worldwide. Burn injuries are characterized by inflammatory processes and alterations in numerous organ systems and functions. Recently, it has become apparent that the gastrointestinal bacterial microbiome is a key component of regulating the immune response and recovery from burn and can also contribute to significant detrimental sequelae after injury, such as sepsis and multiple organ failure. Microbial dysbiosis has been linked to multiple disease states; however, its role in exacerbating acute traumatic injuries, such as burn, is poorly understood. In this article, we review studies that document changes in the intestinal microbiome after burn injury, assess the implications in post-burn pathogenesis, and the potential for further discovery and research.

Circulating sFasL Levels Predict the Severity and Outcome of Burn Injury: A Prospective Observational Study

BACKGROUND

Severe burn injury activates shock, inflammation, and blood cell system, but inappropriate reactions may lead to adverse outcomes. Soluble Fas ligand (sFasL) participates in apoptosis and inflammatory response. The circulating sFasL levels we investigated in association with the burn severity, shock, inflammation, blood cells, and mortality in patients with severe burns.

METHODS

A total of 56 patients with severe burns were recruited. The levels of sFasL and the biomarkers reflecting shock, organ damage, inflammation, and blood cells at 48 h postburn were analyzed. We compared the practical situation of patients that stratified by median sFasL levels and investigated the predictive value of sFasL for mortality.

RESULTS

High circulating sFasL levels were associated with the higher degrees of burn index, shock index, lactate, N-terminal probrain natriuretic peptide, total bilirubin, blood urea nitrogen, creatinine, tumor necrosis factor-α, interleukin-1β, interleukin-8, intercellular adhesion molecule 1, and complement 3, and the lower degrees of oxygenation index, lymphocytes, and platelets. Multiple linear regression analysis showed that the higher tumor necrosis factor-α (P < 0.001) and the lower oxygenation index (P = 0.031) and lymphocytes (P = 0.043) were associated with the higher sFasL. High sFasL (a unit is 50 ng/L) (odds ratio [OR] 5.50 [95% CI 1.04-29.20], P = 0.045) was an independent predictor of increased mortality by multivariate logistic regression analysis.

CONCLUSIONS

High circulating sFasL at 48 h postburn in patients with severe burns reflect shock, proinflammatory response, organ damage, and lymphocyte reductions and predict 30-day mortality.

Investigation and assessment of neutrophil dysfunction early after severe burn injury

BACKGROUND

Extensive burn injury results in a complex immune response that is associated with mortality and prognosis. Studies on acquired immune and the development of sepsis in burn patients have been reported. However, one of the main cells in innate immune, neutrophil dysfunction in the burn shock stage has not been thoroughly characterized.

METHODS

Neutrophil chemotaxis, expression of neutrophil surface markers (P2X1 receptor, [P2RX1]), degranulation (myeloperoxidase [MPO], heparin-binding protein [HBP], matrix metalloproteinase-9 [MMP-9] and neutrophil elastase [NE]), oxidative burst capacity, neutrophil extracellular trap (NET) generation, phagocytosis and apoptosis were measured in 18 patients with major burns (≥30% total body surface area [TBSA]) within 48 h after burn injury. In addition, circulating neutrophils and vascular permeability in mice model with 30% TBSA third-degree burns were also observed and investigated.

RESULTS

Neutrophil functions were reduced considerably in burn shock stage, which was characterized by decreased chemotaxis, phagocytosis and abnormal bactericidal function. Increased release of heparin-binding protein (HBP) and the expression of P2RX1 on the neutrophil surface are related to fluid leakage and decreased chemotaxis during burn shock stage, respectively. The combination of HBP concentration in plasma and P2RX1 expression on neutrophils gives a better prediction of neutrophil dysfunction in burn-injured patients.

CONCLUSION

Neutrophil dysfunction plays a key role in the development of burn injury. Targeting the restoration of neutrophil function may be a feasible therapeutic intervention to help reduce fluid loss during shock and the severity of subsequent infection.

The IL-27 receptor regulates TIGIT on memory CD4+ T cells during sepsis

Sepsis is a leading cause of morbidity and mortality associated with significant impairment in memory T cells. These changes include the upregulation of co-inhibitory markers, a decrease in functionality, and an increase in apoptosis. Due to recent studies describing IL-27 regulation of TIGIT and PD-1, we assessed whether IL-27 impacts these co-inhibitory molecules in sepsis. Based on these data, we hypothesized that IL-27 was responsible for T cell dysfunction during sepsis. Using the cecal ligation and puncture (CLP) sepsis model, we found that IL-27Rα was associated with the upregulation of TIGIT on memory CD4⁺ T cells following CLP. However, IL-27 was not associated with sepsis mortality.

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Numbers of IL-27Rα⁺ memory T cells are decreased following cecal ligation and puncture

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TIGIT is expressed on more IL-27Rα⁺ versus IL-27Rα⁻ memory CD4⁺ T cells during sepsis

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Il27ra^−/− and WT T cells exhibit similar effector function and apoptosis during sepsis

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IL-27 signaling does not impact sepsis mortality

Increased oxidative phosphorylation in lymphocytes does not atone for decreased cell numbers after burn injury

The acute systemic inflammatory response syndrome (SIRS) and multiorgan dysfunction (MOD) that occur in large burn injuries may be attributed, in part, to immunosuppressive responses such as decreased lymphocytes. However, the mitochondrial bioenergetics of lymphocytes after severe burn injury are poorly understood. The purpose of this study was to examine mitochondrial function of lymphocytes following severe burns in a swine model. Anesthetized Yorkshire swine (n = 17) sustained 40% total body surface area full-thickness contact burns. Blood was collected at pre-injury (Baseline; BL) and at 24 and 48 h after injury for complete blood cell analysis, flow cytometry, cytokine analysis, and ficoll separation of intact lymphocytes for high-resolution mitochondrial respirometry analysis. While neutrophil numbers increased, a concomitant decrease was found in lymphocytes (P < 0.001) after burn injury, which was not specific to CD4⁺ or CD8⁺ lymphocytes. No changes in immune cell population were observed from 24 h to 48 h post-injury. IL 12-23 decreased while a transient increase in IL 4 was found from BL to 24h (P < 0.05). CRP progressively increased from BL to 24h (P < 0.05) and 48h (P < 0.001) post-injury. Routine and maximal mitochondrial respiration progressively increased from BL to 24h (P < 0.05) and 48 h post-injury (P < 0.001). No changes were found in leak respiration or residual oxygen consumption. When considering the reduction in lymphocyte number, the total peripheral lymphocyte bioenergetics per volume of blood significantly decreased from BL to 24h and 48h (P < 0.05). For the first time, we were able to measure mitochondrial activity in intact lymphocyte mitochondria through high-resolution respirometry in a severely burned swine model. Our data showed that the non-specific reduction in peripheral T cells after injury was larger than the increased mitochondrial activity in those cells, which may be a compensatory mechanism for the total reduction in lymphocytes. Additional studies in the metabolic activation of T cell subpopulations may provide diagnostic or therapeutic targets after severe burn injury.

Hematopoietic Stem Cell Transplantation Restores Naïve T-Cell Populations in Atm-Deficient Mice and in Preemptively Treated Patients With Ataxia-Telangiectasia

Background: Ataxia-telangiectasia (A-T) is a multisystem disorder with progressive cerebellar ataxia, immunodeficiency, chromosomal instability, and increased cancer susceptibility. Cellular immunodeficiency is based on naïve CD4⁺ and CD8⁺ T-cell lymphopenia. Hematopoietic stem cell transplantation (HSCT) offers a potential to cure immunodeficiency and cancer due to restoration of the lymphopoietic system. The aim of this investigation was to analyze the effect of HSCT on naïve CD4⁺ as well as CD8⁺ T-cell numbers in A-T.

Methods: We analyzed total numbers of peripheral naïve (CD45RA⁺CD62L⁺) and memory (CD45RO⁺CD62L⁻) CD4⁺ and CD8⁺ T-cells of 32 A-T patients. Naïve (CD62L^highCD44^low) and memory (CD62L^lowCD44^high) T-cells were also measured in Atm-deficient mice before and after HSCT with GFP-expressing bone marrow derived hematopoietic stem cells. In addition, we analyzed T-cells in the peripheral blood of two A-T patients after HLA-identic allogeneic HSCT.

Results: Like in humans, naïve CD4⁺ as well as naïve CD8⁺ lymphocytes were decreased in Atm-deficient mice. HSCT significantly inhibited thymic lymphomas and increased survival time in these animals. Donor cell chimerism increased up to more than 50% 6 months after HSCT accompanied by a significant increase of naïve CD4 and CD8 T-cell subpopulations, but not of memory T-cells. This finding was also identified in the blood of the A-T patients after HSCT.

Conclusion: HSCT seems to be a feasible strategy to overcome immunodeficiency and might be a conceivable strategy to avoid T-cell driven cancer in A-T at higher risk for malignancy. Naïve CD4 and CD8 T-cells counts are suitable markers for monitoring immune reconstitution post-HSCT. However, risks and benefits of HSCT in A-T have to be properly weighted.

Amitriptyline Usage Exacerbates the Immune Suppression Following Burn Injury

Currently, over 10% of the US population is taking antidepressants. Numerous antidepressants such as amitriptyline are known to inhibit acid sphingomyelinase (Asm), an enzyme that is known to mediate leukocyte function and homeostasis. Severe burn injury can lead to an immunosuppressive state that is characterized by decreased leukocyte function and numbers as well as increased susceptibility to infection. Based upon the intersection of these facts, we hypothesized that amitriptyline-treated, scald-injured mice would have an altered immune response to injury as compared with untreated scald mice. Prior to burn, mice were pretreated with amitriptyline. Drug- or saline-treated mice were subjected full thickness dorsal scald- or sham-injury. Immune cells from spleen, thymus, and bone marrow were subsequently harvested and characterized. We first observed that amitriptyline prior to burn injury increased body mass loss and spleen contraction. Both amitriptylinetreatment and burn injury resulted in a 40% decrease of leukocyte Asm activity. Following scald injury, we demonstrate increased reduction of lymphocyte precursors in the bone marrow and thymus, as well as mature leukocytes in the spleen in mice that were treated with amitriptyline. We also demonstrate that amitriptyline treatment prior to injury reduced neutrophil accumulation following peptidoglycan stimulus in scald-injured mice. These data show that Asm alterations can play a significant role in mediating alterations to the immune system after injury. The data further suggest that those taking antidepressants may be at a higher risk for complications following burn injury.

Bronchoalveolar Lavage Microvesicles Protect Burn-Injured Mice from Pulmonary Infection

BACKGROUND

Pseudomonas aeruginosa is a major cause of morbidity and mortality among burn patients, despite antibiotic therapy. There is a need to identify innate immune defenses that prevent P aeruginosa infection in injured adults in an effort to find therapeutic alternatives to antibiotics. Here, we tested our hypothesis that microvesicles (MVs) in bronchoalveolar (BAL) fluid have a role in the immunity of the lung in response to pathogens.

STUDY DESIGN

Microvesicles were isolated from murine BAL fluid, quantified using Nanoparticle Tracking Analysis, and injected into burn-injured mice before P aeruginosa infection. Survival was assessed and BAL bacterial loads enumerated. Neutrophil number and interleukin 6 activity were determined. Lungs were harvested and sphingosine (SPH) content analyzed via immunohistochemistry. Antimicrobial effects of MVs and SPH-enriched MVs were assessed in an in vitro assay.

RESULTS

Burn-injured mice have reduced BAL MV number and SPH content compared with sham. When BAL MVs from healthy mice are administered to injured mice, survival and bacterial clearance are improved robustly. We also observed that intranasal administration of MVs restores SPH levels after burn injury, MVs kill bacteria directly, and this bacterial killing is increased when the MVs are supplemented with SPH.

CONCLUSIONS

Using a preclinical model, BAL MVs are reduced after scald injury and BAL MV restoration to injured mice improves survival and bacterial clearance. The antimicrobial mechanisms leading to improved survival include the quantity and SPH content of BAL MVs.

Glucocorticoid receptor expression and binding capacity in patients with burn injury

BACKGROUND

Burn injuries are associated with strong inflammation and risk of secondary sepsis which both may affect the function of the glucocorticoid receptor (GR). The aim of this study was to determine GR expression and binding capacity in leucocytes from patients admitted to a tertiary burn center.

METHODS

Blood was sampled from 13 patients on admission and days 7, 14 and 21, and once from 16 healthy subjects. Patients were grouped according to the extent of burn and to any sepsis on day 7. Expression and binding capacity of GR were determined as arbitrary units using flow cytometry.

RESULTS

GR expression and binding capacity were increased compared to healthy subjects in most circulating leucocyte subsets on admission irrespective of burn size. Patients with sepsis on day 7 displayed increased GR expression in T lymphocytes (51.8%, P < 0.01) compared to admission. There was a negative correlation between GR binding capacity in neutrophils and burn size after 14 days (P < 0.05).

CONCLUSIONS

GR expression and binding capacity are increased in most types of circulating leucocytes of severely burned patients on their admission to specialized burn care. If sepsis is present after 1 week, it is associated with higher GR expression in T lymphocytes and NK cells.

Xenogeneic Mesenchymal Stromal Cells Improve Wound Healing and Modulate the Immune Response in an Extensive Burn Model

Major skin burns are difficult to treat. Patients often require special care and long-term hospitalization. Besides specific complications associated with the wounds themselves, there may be impairment of the immune system and of other organs. Mesenchymal stromal cells (MSCs) are a recent therapeutic alternative to treat burns, mainly aiming to accelerate the healing process. Several MSC properties favor their use as therapeutic approach, as they promote angiogenesis, stimulate regeneration, and enhance the immunoregulatory function. Moreover, since patients with extensive burns require urgent treatment and because the expansion of autologous MSCs is a time-consuming process, in this present study we chose to evaluate the therapeutic potential of xenogeneic MSCs in the treatment of severe burns in rats. MSCs were isolated from mouse bone marrow, expanded in vitro, and intradermally injected in the periphery of burn wounds. MSC-treated rats presented higher survival rates (76.19%) than control animals treated with PBS (60.86%, p < 0.05). In addition, 60 days after the thermal injury, the MSC-treated group showed larger proportion of healed areas within the burn wounds (90.81 ± 5.05%) than the PBS-treated group (76.11 ± 3.46%, p = 0.03). We also observed that CD4(+) and CD8(+) T cells in spleens and in damaged skin, as well as the percentage of neutrophils in the burned area, were modulated by MSC treatment. Plasma cytokine (TGF-β, IL-10, IL-6, and CINC-1) levels were also altered in the MSC-treated rats, when compared to controls. Number of injected GFP(+) MSCs progressively decreased over time, and 60 days after injection, few MSCs were still detected in the skin of treated animals. This study demonstrates the therapeutic effectiveness of intradermal application of MSCs in a rat model of deep burns, providing basis for future regenerative therapies in patients suffering from deep burn injuries.

G-CSF drives a posttraumatic immune program that protects the host from infection

Traumatic injury is generally considered to have a suppressive effect on the immune system, resulting in increased susceptibility to infection. Paradoxically, we found that thermal injury to the skin induced a robust time-dependent protection of mice from a lethal Klebsiella pneumoniae pulmonary challenge. The protective response was neutrophil dependent and temporally associated with a systemic increase in neutrophils resulting from a reprioritization of hematopoiesis toward myeloid lineages. A prominent and specific activation of STAT3 in the bone marrow preceded the myeloid shift in that compartment, in association with durable increases in STAT3 activating serum cytokines G-CSF and IL-6. Neutralization of the postburn increase in serum G-CSF largely blocked STAT3 activation in marrow cells, reversing the hematopoietic changes and systemic neutrophilia. Daily administration of rG-CSF was sufficient to recapitulate the changes induced by injury including hematopoietic reprioritization and protection from pulmonary challenge with K. pneumoniae. Analysis of posttraumatic gene expression patterns in humans reveals that they are also consistent with a role for G-CSF as a switch that activates innate immune responses and suppresses adaptive immune responses. Our findings suggest that the G-CSF STAT3 axis constitutes a key protective mechanism induced by injury to reduce the risk for posttraumatic infection.

Clinical impact of altered T-cell homeostasis in treated HIV patients enrolled in a large observational cohort

OBJECTIVE(S)

We investigated the probability of transitioning in or out of the CD3⁺ T-cell homeostatic range during antiretroviral therapy, and we assessed the clinical impact of lost T-cell homeostasis (TCH) on AIDS-defining illnesses (ADIs) or death.

DESIGN

Within the Canadian Observational Cohort (CANOC), we studied 4463 antiretroviral therapy (ART)-naive HIV-positive patients initiating combination ART (cART) between 2000 and 2010.

METHODS

CD3⁺ trajectories were estimated using a four state Markov model. CD3⁺ T-cel percentage states were classified as follows: very low (<50%), low (50-64%), normal (65-85%), and high (>85%). Covariates associated with transitioning between states were examined. The association between CD3⁺ T-cell percentage states and time to ADI/death from cART initiation was determined using Cox proportional hazards models.

RESULTS

A total of 4463 patients were followed for a median of 3 years. Two thousand, five hundred and eight (56%) patients never transitioned from their baseline CD3⁺ T-cell percentage state; 85% of these had normal TCH. In multivariable analysis, individuals with time-updated low CD4⁺ cell count, time-updated detectable viral load, older age, and hepatitis C virus (HCV) coinfection were less likely to maintain TCH. In the multivariable proportional hazards model, both very low and high CD3⁺ T-cell percentages were associated with increased risk of ADI/death [adjusted hazard ratio=1.91 (95% confidence interval, CI: 1.27-2.89) and hazard ratio=1.49 (95% CI: 1.13-1.96), respectively].

CONCLUSION

Patients with very low or high CD3⁺ T-cell percentages are at risk for ADIs/death. To our knowledge, this is the first study linking altered TCH and morbidity/mortality in cART-treated HIV-positive patients.

OX62+OX6+OX35+ rat dendritic cells are unable to prime CD4+ T cells for an effective immune response following acute burn injury

Co-stimulatory molecules expressed on Dendritic Cells (DCs) function to coordinate an efficient immune response by T cells in the peripheral lymph nodes. We hypothesized that CD4+ T cell-mediated immune suppression following burn injury may be related to dysfunctional DCs residing in gut associated lymphoid tissues (GALT), such as Mesenteric Lymph Nodes (MLN). Therefore, we studied co-stimulatory molecules expressed on burn rat MLN DCs as an index of functional DCs that would mount an effective normal CD4+ T cell immune response. In a rat model of 30% Total Body Surface Area (TBSA) scald burn, OX62+OX6+OX35+ DCs and CD4+ T cells were isolated from MLN of day 3 post-burn and sham control rats. DCs were tested for their expression of co-stimulatory molecules, and prime CD4+ T cell (DC:CD4+T cell co-culture assays) to determine an effector immune response such as CD4+ T cell proliferation. The surface receptor expressions of MLN DCs co-stimulatory molecules, i.e., MHC-II, CD40, CD80 (B7-1), and CD86 (B7-2) were determined by Flow cytometry (quantitatively) and confocal microscopy (qualitatively). Tritiated thymidine and CFDA-SE determined CD4+ T cell proliferation following co-incubation with DCs. Cytokine milieu of MLN (IL-12 and IL-10) was assessed by mRNA determination by RT-PCR. The results showed down-regulated expressions of co-stimulatory markers (CD80, CD86, CD40 and MHC-II) of MLN DCs obtained from burn-injured rats, as well as lack of ability of these burn-induced DCs to stimulate CD4+ T cell proliferation in co-culture assays, as compared to the sham rats. Moreover, anti-CD40 stimulation of affected burn MLN DCs did not reverse this alteration. Furthermore, a marked up-regulation of mRNA IL-10 and down-regulation of mRNA IL-12 in burn MLN as compared to sham animals was also observed. To surmise, the data indicated that dysfunctional OX62+OX6+OX35+ rat MLN DCs may contribute to CD4+ T-cell-mediated immune suppression observed following acute burn injury.

Overactivation of mitogen-activated protein kinase and suppression of mitofusin-2 expression are two independent events in high mobility group box 1 protein-mediated T cell immune dysfunction

High mobility group box 1 protein (HMGB1), a critical proinflammatory cytokine, has recently been identified to be an immunostimulatory signal involved in sepsis-related immune dysfunction when released extracellularly, but the potential mechanism involved remains elusive. Here, we showed that the treatment with HMGB1 in vitro inhibited T lymphocyte immune response and expression of mitofusin-2 (Mfn-2; a member of the mitofusin family) in a dose- and time-dependent manner. Upregulation of Mfn-2 expression attenuated the suppressive effect of HMGB1 on T cell immune function. The phosphorylation of both extracellular signal-regulated kinase (ERK)1/2 and p38 mitogen-activated protein kinase (MAPK) was markedly upregulated by treating with high amount of HMGB1, while pretreatment with ERK1/2 and p38 MAPK-specific inhibitors (U0126 and SB203580) could attenuate suppression of T cell immune function and nuclear factor of activated T cell (NFAT) activation induced by HMGB1, respectively. HMGB1-induced activity of ERK1/2 and p38 was not fully inhibited in the presence of U0126 or SB203580. Interestingly, overexpression of Mfn-2 had no marked effect on HMGB1-mediated activation of MAPK, but could attenuate the suppressive effect of HMGB1 on the activity of NFAT. Thus, the mechanisms involved in HMGB1-induced T cell immune dysfunction in vitro at least partly include suppression of Mfn-2 expression, overactivation of ERK1/2, p38 MAPK, and intervention of NFAT activation, while the protective effect of Mfn-2 on T cell immune dysfunction induced by HMGB1 is dependent on other signaling pathway associated with NFAT, but not MAPK. Taken together, we conclude that overactivation of MAPK and suppression of Mfn-2 expression are two independent events in HMGB1-mediated T cell immune dysfunction.

The Effect of Tumor Necrosis Factor-α-Induced Protein 8 Like-2 on Immune Response of CD4+T Lymphocytes in Mice after Thermal Injury

The status of cellular immunity has been shown to be associated with the occurrence and development of sepsis. Accumulating evidence has demonstrated that tumor necrosis factor-α-induced protein 8 like-2 (TIPE2) plays an important role in maintaining homeostasis of immune function. The present study, with the use of a controlled in vivo approach, demonstrated the effect of TIPE2 on cell-mediated immunity of CD4+ T lymphocytes in thermal injury murine model. One hundred and twenty-eight male mice were randomly allocated into four groups, which were sham burn group (n=48), burn group (n=48), burn with lentivirus-RNAi-TIPE2 transfection group (n=16), burn with negative control transfection group (n=16), and they were sacrificed at the designated time points. CD4+ T lymphocytes were isolated from the spleen using MACS microbeads. Phenotypes were analyzed by flow cytometry analysis, and cytokines were determined using ELISA kits. We found that the expression of TIPE2 was markedly increased in CD4+T lymphocytes in mice at 24,48 and 72 hours postburn. Down-regulation of TIPE2 by lentivirus-RNAi-TIPE2 attenuated the suppressive effect of CD4+T lymphocytes, which was associated with profound elevation of nuclear factor of activated T cell (NF-AT) activity. These results demonstrate that TIPE2 appear to be involved in the immune regulation of CD4+ T lymphocytes, and the decrease in TIPE2 expression on CD4+T lymphocytes in vivo can enhance peripheral T lymphocyte function after thermal injury. These data might provide a valid strategy to prevent the development of immunosuppressive state resulted from major burns.

Burn-injury affects gut-associated lymphoid tissues derived CD4+ T cells

After scald burn-injury, the intestinal immune system responds to maintain immune balance. In this regard CD4+T cells in Gut-Associated Lymphoid Tissues (GALT), like mesenteric lymph nodes (MLN) and Peyer's patches (PP) respond to avoid immune suppression following major injury such as burn. Therefore, we hypothesized that the gut CD4+T cells become dysfunctional and turn the immune homeostasis towards depression of CD4+ T cell-mediated adaptive immune responses. In the current study we show down regulation of mucosal CD4+ T cell proliferation, IL-2 production and cell surface marker expression of mucosal CD4+ T cells moving towards suppressive-type. Acute burn-injury lead to up-regulation of regulatory marker (CD25+), down regulation of adhesion (CD62L, CD11a) and homing receptor (CD49d) expression, and up-regulation of negative co-stimulatory (CTLA-4) molecule. Moreover, CD4+CD25+ T cells of intestinal origin showed resistance to spontaneous as well as induced apoptosis that may contribute to suppression of effector CD4+ T cells. Furthermore, gut CD4+CD25+ T cells obtained from burn-injured animals were able to down-regulate naïve CD4+ T cell proliferation following adoptive transfer of burn-injured CD4+CD25+ T cells into sham control animals, without any significant effect on cell surface activation markers. Together, these data demonstrate that the intestinal CD4+ T cells evolve a strategy to promote suppressive CD4+ T cell effector responses, as evidenced by enhanced CD4+CD25+ T cells, up-regulated CTLA-4 expression, reduced IL-2 production, tendency towards diminished apoptosis of suppressive CD4+ T cells, and thus lose their natural ability to regulate immune homeostasis following acute burn-injury and prevent immune paralysis.

Therapeutic efficacy of an antibiotic-loaded nanosheet in a murine burn-wound infection model

Polymeric ultra-thin films (nanosheets) possess unique properties that make them suitable materials for various biomedical applications. In our previous study, we assessed the use of an antibiotic (tetracycline, TC)-loaded nanosheet (or "TC-nanosheet") for the treatment of gastrointestinal tissue defects. The nanosheet consisted of three functional layers: layer-by-layer nanosheet as a stable platform, TC as an antimicrobial agent with autofluorescence for tracing, and a poly(vinyl acetate) nanosheet to act as a protecting layer. The TC-nanosheet has high flexibility, adhesive strength and transparency. Here, we evaluated the effectiveness of the TC-nanosheet in preventing full thickness burn-wound infections. In an in vivo study, murine dorsal skin was injured by full-thickness burns and then infected with Pseudomonas aeruginosa (P. aeruginosa), a common bacterium causing burn-associated infections. The wound site was treated either with a TC-nanosheet, TC-unloaded nanosheet or left untreated. Wound management was facilitated by the high transparency of the TC-nanosheet. The TC-nanosheet significantly improved burn-wound infection by P. aeruginosa in mice. Indeed, all mice treated with the TC-nanosheet survived, whereas the other treatment groups displayed increased rates of mortality due to bacterial infection. According to histological analyses and viable bacterial counting in the liver (bacterial translocation), the TC-nanosheets were able to prevent not only the local inflammation but also systemic inflammation. We conclude that the TC-nanosheet can act as an effective treatment for full-thickness burn-wound infection. Hence, the TC-nanosheet is a promising therapeutic tool for burn-wound management in severely burn-injured patients.

Treatment with gelsolin reduces brain inflammation and apoptotic signaling in mice following thermal injury

Background

Burn survivors develop long-term cognitive impairment with increased inflammation and apoptosis in the brain. Gelsolin, an actin-binding protein with capping and severing activities, plays a crucial role in the septic response. We investigated if gelsolin infusion could attenuate neural damage in burned mice.

Methods

Mice with 15% total body surface area burns were injected intravenously with bovine serum albumin as placebo (2 mg/kg), or with low (2 mg/kg) or high doses (20 mg/kg) of gelsolin. Samples were harvested at 8, 24, 48 and 72 hours postburn. The immune function of splenic T cells was analyzed. Cerebral pathology was examined by hematoxylin/eosin staining, while activated glial cells and infiltrating leukocytes were detected by immunohistochemistry. Cerebral cytokine mRNAs were further assessed by quantitative real-time PCR, while apoptosis was evaluated by caspase-3. Neural damage was determined using enzyme-linked immunosorbent assay of neuron-specific enolase (NSE) and soluble protein-100 (S-100). Finally, cerebral phospho-ERK expression was measured by western blot.

Results

Gelsolin significantly improved the outcomes of mice following major burns in a dose-dependent manner. The survival rate was improved by high dose gelsolin treatment compared with the placebo group (56.67% vs. 30%). Although there was no significant improvement in outcome in mice receiving low dose gelsolin (30%), survival time was prolonged against the placebo control (43.1 ± 4.5 h vs. 35.5 ± 5.0 h; P < 0.05). Burn-induced T cell suppression was greatly alleviated by high dose gelsolin treatment. Concurrently, cerebral abnormalities were greatly ameliorated as shown by reduced NSE and S-100 content of brain, decreased cytokine mRNA expressions, suppressed microglial activation, and enhanced infiltration of CD11b+ and CD45+ cells into the brain. Furthermore, the elevated caspase-3 activity seen following burn injury was remarkably reduced by high dose gelsolin treatment along with down-regulation of phospho-ERK expression.

Conclusion

Exogenous gelsolin infusion improves survival of mice following major burn injury by partially attenuating inflammation and apoptosis in brain, and by enhancing peripheral T lymphocyte function as well. These data suggest a novel and effective strategy to combat excessive neuroinflammation and to preserve cognition in the setting of major burns.

Th17 (IFNγ- IL17+) CD4+ T cells generated after burn injury may be a novel cellular mechanism for postburn immunosuppression

BACKGROUND

The mechanism responsible for initiating and controlling the immunosuppressive response after burn injury remains unknown. Interleukin-17 (IL-17) secreting Th17 (interferon [IFN]γ IL17) cells are a novel subset of CD4 T cells associated with a weak, proinflammatory response that antagonizes the proinflammatory Th1 (IFNγ IL17) response. Given that transforming growth factor-β and IL6 mediate Th17 cell development, we hypothesized that burn injury may generate Th17 cells that could mediate postburn immunosuppression.

METHODS

After a 20% total body surface area burn in female C57BL/6 mice, wound-draining lymph nodes were harvested 3 days, 7 days, or 14 days after injury. CD4 T cells were enriched by magnetic selection, and flow cytometry was used to identify intracellular IL17 and IFNγ in CD3CD4 T cells. Additional purified CD3CD4 T cells were cultured with Th17 polarizing IL6 and transforming growth factor-β for 4 days, and flow cytometry was again used to identify intracellular IL17 and IFNγ in CD4 T cells.

RESULTS

The number and percentage of preformed Th17 cells was significantly greater in burn mice compared with sham at all time points. In addition, the ratio of Th17 cells to Th1 cells was always significantly higher in burn mice compared with sham. These differences were eliminated in Th17 polarizing conditions in vitro. CD4 T cells never generated both IL17 and IFNγ.

CONCLUSION

These results demonstrate for the first time that Th17 cells (IFNγ IL17) are spontaneously generated after burn injury. Given that Th17 cells (IFNγ IL17) are antagonistic to Th1 (IFNγ IL17) cells, these results suggest a novel mechanism for initiating and controlling postburn immunosuppression that deserves further investigation.

Astragalus polysaccharides attenuate postburn sepsis via inhibiting negative immunoregulation of CD4+ CD25(high) T cells

BACKGROUND

Astragalus polysaccharides (APS) isolated from one of the Chinese herbs, Astragalus mongholicus, are known to have a variety of immunomodulatory activities. However, it is not yet clear whether APS can exert an effect on the immune functions of regulatory T cells (Tregs). This study was carried out to investigate the effect of APS on the immune function of peripheral blood Tregs in postburn sepsis.

METHODOLOGY/PRINCIPAL FINDINGS

BALB/C mice were randomly divided into six groups as follows: sham burn group, burn control (burn without infection animals) group, burn plus P. aeruginosa group, burn plus P. aeruginosa with APS (50 mg/kg) treatment group, burn plus P. aeruginosa with APS (100 mg/kg) treatment group, and burn plus P. aeruginosa with APS (200 mg/kg) treatment group, and they were sacrificed on postburn day 1, 3, 5, and 7, respectively, with seven animals at each time point. Magnetic microbeads were used to isolate peripheral blood Tregs and CD4(+) T cells. Phenotypes were analyzed by flow cytometry, and cytokine levels were determined with ELISA. In the burn plus P. aeruginosa group, forkhead/winged helix transcription factor p3 (Foxp3) expression on CD4(+)CD25(+)Tregs were strongly enhanced in comparison to the sham group, and the capacity of CD4(+)CD25(+)Tregs to produce interleukin (IL)-10 was markedly increased. Administration of APS to inhibit CD4(+)CD25(+)Tregs could significantly decrease expression of Foxp3 on CD4(+)CD25(+)Tregs, and IL-10 production in burned mice with P. aeruginosa infection. At the same time, proliferative activity and expression of IL-2 and IL-2Rα on CD4(+) T cells were restored. In contrast, anti-Toll-like receptor 4 (TLR4) antibody could block the effect of APS on Tregs immune function.

CONCLUSION

APS might suppress CD4(+)CD25(+)Treg activity, at least in part, via binding TLR4 on Tregs and trigger a shift of Th2 to Th1 with activation of CD4(+) T cells in burned mice with P. aeruginosa infection.

Astragalus polysaccharides attenuate postburn sepsis via inhibiting negative immunoregulation of CD4+ CD25(high) T cells

Backgroud

Astragalus polysaccharides (APS) isolated from one of the Chinese herbs, Astragalus mongholicus, are known to have a variety of immunomodulatory activities. However, it is not yet clear whether APS can exert an effect on the immune functions of regulatory T cells (Tregs). This study was carried out to investigate the effect of APS on the immune function of peripheral blood Tregs in postburn sepsis.

Methodology/Principal Findings

BalB/c mice were randomly divided into six groups as follows: sham burn group, burn control(burn without infection animals) group, burn plus P. aeruginosa group, burn plus P. aeruginosa with APS (50 mg/kg) treatment group, burn plus P. aeruginosa with APS (100 mg/kg) treatment group, and burn plus P. aeruginosa with APS (200 mg/kg) treatment group, and they were sacrificed on postburn day 1, 3, 5, and 7, respectively, with seven animals at each time point. Magnetic microbeads were used to isolate peripheral blood Tregs and CD4⁺ T cells. Phenotypes were analyzed by flow cytometry, and cytokine levels were determined with ELISA. In the burn plus P. aeruginosa group, forkhead/winged helix transcription factor p3 (Foxp3) expression on CD4⁺CD25⁺Tregs were strongly enhanced in comparison to the sham group, and the capacity of CD4⁺CD25⁺Tregs to produce interleukin (IL)-10 was markedly increased. Administration of APS to inhibit CD4⁺CD25⁺Tregs could significantly decrease expression of Foxp3 on CD4⁺CD25⁺Tregs, and IL-10 production in burned mice with P. aeruginosa infection. At the same time, proliferative activity and expression of IL-2 and IL-2Rα on CD4⁺ T cells were restored. In contrast, anti-Toll-like receptor 4 (TLR4) antibody could block the effect of APS on Tregs immune function.

Conclusion

APS might suppress CD4⁺CD25⁺Treg activity, at least in part, via binding TLR4 on Tregs and trigger a shift of Th2 to Th1 with activation of CD4⁺ T cells in burned mice with P. aeruginosa infection.

High mobility group box 1 protein suppresses T cell-mediated immunity via CD11c(low)CD45RB(high) dendritic cell differentiation

AIM

High mobility group box 1 protein (HMGB1) has been identified as a late proinflammatory cytokine and plays a key role in immune regulation. However, it is not yet clear whether HMGB1 can induce the activation and differentiation of dendritic cell (DC) subsets and subsequently modulate immune function of T cells. This study was performed to investigate the effect of HMGB1 on the differentiation of splenic DCs and its influence on T cell-mediated immunity in terms of DC subsets CD11c(low)CD45RB(high) DCs and CD11c(high)CD45RB(low) DCs in male BALB/c mice spleens in vitro.

RESULTS

MACS microbeads were used to isolate splenic DCs, CD11c(low)CD45RB(high) DCs, CD11c(high)CD45RB(low) DCs and CD4(+) T cells. The percentage of CD11c(low)CD45RB(high) DCs was significantly increased after treatment with HMGB1 compared to their counterparts (CD11c(high)CD45RB(low) DCs). It was found that unlike the gradually increasing interleukin (IL)-12 secretion of CD11c(high)CD45RB(low) DCs induced by HMGB1, CD11c(low)CD45RB(high) DCs showed a obvious dose-dependent response between IL-10 production and HMGB1 stimulation. In order to verify whether the alteration of CD4(+) T cells was mainly associated with the differentiation of splenic DCs mediated by HMGB1 to CD11c(low)CD45RB(high) DCs, anti-IL-12 receptor (IL-12R) or anti-IL-10R monoclonal antibody was used to inhibit the effect of CD11c(high)CD45RB(low) DCs or CD11c(low)CD45RB(high) DCs in CD4(+) T cells mixed lymphocyte reaction culture. After treatment with anti-IL-12R or anti-IL-10 monoclonal antibody in CD4(+) T cells+CD11c(high)CD45RB(low) DCs or CD11c(low)CD45RB(high) DCs mixed lymphocyte reaction, the induction of these DCs on T cells was inhibited dramatically.

CONCLUSION

These data demonstrated that HMGB1 might induce the differentiation of splenic DCs to CD11c(low)CD45RB(high) DCs followed by shifting of Th1 to Th2 with enhancement of T lymphocyte immune function in vitro. Also, the effect of HMGB1 on T cell differentiation to Th2 was not associated with the inhibition of IL-12 production in CD11c(high)CD45RB(low) DCs.

Association between high-mobility group box-1 protein release and immune function of dendritic cells in thermal injury

The present study was performed to investigate in vivo the effect of high-mobility group box-1 protein (HMGB1) on the maturation of dendritic cell (DC) and the influence on T-cell-mediated immunity after thermal injury. Rats were randomly divided into 3 groups as follows: sham burn group, burn group, and burn with ethyl pyruvate (EP) treatment group, and they were sacrificed on post burn days (PBD) 1, 3, 5, and 7 respectively. MACS microbeads were used to isolate splenic DCs and column of nylon wool to obtain T cells. Phenotypes were analyzed by flow cytometry and cytokines were determined with ELISA kits. The expression levels of splenic HMGB1 were significantly elevated during PBD 1-7. DC expressed similar CD80 levels, strongly enhanced CD86, and slightly elevated MHC class II levels in comparison to DC from sham-injured rats, and protein levels of IL-12 were not increased after thermal injury. Administration of EP to inhibit HMGB1 could significantly enhance expression levels of CD80, MHC class II on DC surface, and IL-12 production after burns. Simultaneously, proliferative activity and expression levels of IL-2 as well as IL-2R alpha of T cell were restored. These results suggested that the excessively released HMGB1 might stimulate splenic DC to mature abnormally and down-regulate the IL-12 production, and further shifting of Th1 to Th2 with suppression of T-lymphocyte immune function following burn injury.

T cells from burn-injured mice demonstrate a loss of sensitivity to glucocorticoids

Glucocorticoids (GC) are steroid hormones that modulate T cell functions and restrain their hyperresponsiveness following stimulation. Naive T lymphocytes are sensitive to GC but become more resistant when they are activated. A balance between activation and inhibition signals is important for a targeted and effective T cell response. Thermal injury is characterized by an immune dysfunction and hyperactive T cells visible at day 10 postburn. In this study, our objective was to evaluate T cell sensitivity to GC following thermal injury and to identify mechanisms that could modulate their sensitivity. One mechanism that we hypothesized was increased p38 mitogen-activated protein kinase (MAPK) activity that could lead to GC resistance. Male C57BL/6 mice underwent a full-thickness 20% total body surface area. At 10 days postinjury, splenic T cells were isolated. Glucocorticoid receptor (GR) expression was higher in T cells from burn-injured mice. Interestingly, these cells were also less sensitive to GC-induced apoptosis prior to and poststimulation. Furthermore, anti-CD3-activated T cells from burn-injured mice showed increased proliferation and CD25 expression, which resisted corticosterone's (CORT) suppressive effect. Anti-CD3-activated CD4(+)CD44(+) memory cells from burn-injured mice expressed the highest level of CD25 and were resistant to CORT. Increased phosphorylation of p38 MAPK was also noted in activated T cells from burn-injured mice. Pharmacological inhibition of p38 MAPK decreased cell proliferation and normalized interferon-gamma (IFNgamma) production. In conclusion, we demonstrate that a unique event like burn injury induces a loss of sensitivity to GC in splenic T cells and have identified p38 MAPK as a key modulator for this resistance.

Selective effect of burn injury on splenic CD11c(+) dendritic cells and CD8alpha(+)CD4(-)CD11c(+) dendritic cell subsets

Burn injury causes an immunosuppression associated with suppressed adaptive immune function. Dendritic cells (DCs) are APCs for which signaling via their Toll-like receptors (TLRs) induces their maturation and activation, which is essential for the adaptive immune response. In this study, we examined if burn injury alters the TLR activity of splenic DCs. After injury, we noticed that DC functions were impaired, characterized by a suppressed capacity to prime naive T cells when triggering the TLR4 signaling cascade using specific ligands (LPS or rHSP60). The observed perturbations on LPS-primed DCs isolated from burned mice exhibited significantly diminished IL-12p40 production and enhanced IL-10 secretion-associated impairment in mitogen-activated protein kinase activation. Interestingly, we observed a decrease of TLR4/MD-2 expression on the CD8alpha(+) DC subset that persisted following LPS stimulation. The altered TLR4 expression on LPS-stimulated CD8alpha(+) DCs was associated with reduced capacity to produce IL-12 after stimulation. Our results suggested that TLR4 reactivity on DCs, especially CD8alpha(+) DCs, is disturbed after burn injury.

Effects of early enteral nutrition supplemented with arginine on intestinal mucosal immunity in severely burned mice

BACKGROUND

To investigate the effects of early enteral nutrition (EN) supplemented with Arginine (Arg) on intestinal mucosal immunity in severely burned mice.

METHODS

Forty-four mice were randomly assigned into four groups: a sham injury+EN group (n=10), a sham injury+EN+Arg group (n=10), a burn+EN group (n=12), and a burn+EN+Arg group (n=12) and the mice in two experimental groups received a 20% total body surface area (TBSA), full-thickness scald burn on the back. Then, the burned mice were given a 175 kcal/kg body wt/day of conventional enteral nutrition or an isonitrogenous and isocaloric enteral nutrition supplemented with Arg by gastric gavage for 7 days. There was isonitrogenous and isocaloric intake in two experimental groups. The mice in two control groups received the same procedures as above, except for burn injury. On day 7 after injury, all mice among four groups were euthanized and the entire intestine was harvested. Intestinal immunoglobulin A (IgA) levels, total lymphocyte yield, and lymphocyte subpopulations in Peyer's patches were analyzed. Levels of IFN-gamma, IL-2, IL-4 and IL-10 in gut homogenates were also measured by ELISA.

RESULTS

Total lymphocyte yield, numbers of lymphocyte subpopulations, and intestinal IgA levels in the EN+ARG group were higher than those in the EN group (p<0.05). Levels of gut tissue cytokines were significantly altered with enteral Arg supplementation: levels of IL-4 and IL-10 were increased, and levels of IFN-gamma and IL-2 declined, when compared with the EN-fed mice (p<0.05).

CONCLUSIONS

The results of this study suggested that enteral nutrition supplemented with Arg has changed the cytokine concentrations in intestinal homogenates from a pro- to an anti-inflammatory profile, increased sIgA levels and changed lymphocytes in severely burned mice.

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.

The effect of high-mobility group box 1 protein on activity of regulatory T cells after thermal injury in rats

The aim of the present study was to investigate in vivo the effect of high-mobility group box 1 protein (HMGB1) on activity of regulatory T cells (Tregs) and the influence on T-cell-mediated immunity after thermal injury. Male Wistar rats were randomly divided into four groups as follows: sham burn group, burn group, burn with ethyl pyruvate treatment group, and burn with antireceptor for advanced glycation end products (RAGE) antibody treatment group, and they were killed on postburn days 1, 3, 5, and 7, respectively, with eight animals at each time point. Magnetic cell sorting microbeads were used to isolate splenic Tregs and a column of nylon wool to obtain T cells. Phenotypes, including cytotoxic T-lymphocyte-associated antigen 4 (CTLA-4), forkhead/winged helix transcription factor p3 (Foxp3), RAGE, and IL-2Ralpha, were analyzed by flow cytometry. Levels of HMGB1, IL-10, IL-2, IL-4 and interferon gamma were determined by enzyme-linked immunosorbent assay kits, and real-time reverse transcription-polymerase chain reaction was performed to detect mRNA expression of IL-10, IL-2, and IL-2Ralpha. Serum HMGB1 levels were significantly elevated during postburn days 1 to 7. In the burn group, CTLA-4 and Foxp3 expression levels of Tregs were strongly enhanced in comparison to the sham-injured group, and the capacity of Tregs to produce IL-10 was markedly increased. Administration of ethyl pyruvate to inhibit HMGB1 or anti-RAGE antibody could significantly decrease expression levels of CTLA-4, Foxp3 on Tregs, and IL-10 production after burns. Simultaneously, proliferative activity and expression levels of IL-2 and IL-2Ralpha of T cell were restored. The excessively released HMGB1 might stimulate CD4+CD25+Treg activity via binding RAGE on the surface of Tregs and trigger a shift of T(H)1 to T(H)2 with suppression of T-lymphocyte immune function after burn injury.

The influence of Peyer's patch apoptosis on intestinal mucosal immunity in burned mice

The aim of this study was to investigate the influence of apoptosis on Peyer's patches and the intestinal immunoglobulin A (IgA) response in burned mice. Sixty male Balb/c mice were randomly assigned into the sham-burn (control) group (n=30) and the burn group (n=30). The mice in the burn group received a full-thickness scald burn over 20% of the total body surface area (TBSA), on the back. At 12, 24 and 72 h, respectively, after injury, the burned mice (n=10, at every time point) were anaesthetised and their entire intestines were collected. The mice in the sham-burn group were treated with the same procedure as above, except for the burn injury. The number of Peyer's patches on every entire intestine and the total Peyer's patches cell yield were counted. The changes of lymphocyte subpopulations in Peyer's patches were measured by flow cytometry (FCM). And the levels of intestinal IgA were examined by enzyme-linked immunosorbent assay (ELISA). Fluoresceinisothiocyanate (FITC)-conjugated Annexin-tau and propidium iodide (PI) double-staining cells were analysed by FCM for apoptotic ratio in Peyer's patches. The results showed that the total Peyer's patch cell yield and the numbers of CD3, CD4, CD8 and CD19 cells were significantly decreased at 12, 24 and 72 h after injury (P<0.05), and that the intestinal IgA levels were markedly reduced at 24 and 72 h (P<0.05). On the other hand, total apoptotic ratio and all cell subpopulation apoptosis in Peyer's patches were dramatically increased at 12, 24 and 72 h after injury (P<0.05). These results indicated that severe burns led to a significant decrease in the number of Peyer's patch cells and in intestinal IgA levels, which was closely associated with strongly increased apoptosis in Peyer's patches.

Relationship between high-mobility group box 1 protein release and T-cell suppression in rats after thermal injury

To study whether high-mobility group box 1 protein (HMGB1) has an effect on T-cell-mediated immunity secondary to burn injury, 96 male Wistar rats weighing 250 to 300 g were randomly divided into three groups as follows:sham burn group, burn group, and burn with ethyl pyruvate treatment group, and they were killed on postburn days (PBDs)1, 3, 5, and 7, respectively, with 8 animals at each time point. Columns of nylon wool were used to isolate splenic T cells. T-Cell proliferation was analyzed with thiazolyl blue and expression of IL-2 receptor alpha (IL-2Ralpha) on the surface of T cell with flow cytometry. Levels of HMGB1 were determined using Western blot analysis. IL-2, soluble IL-2R, IL-4, and interferon-gamma were determined with enzyme-linked immunosorbent assay kits. Gene expressions of HMGB1, IL-2, and IL-2R were assessed using reverse-transcription polymerase chain reaction, and activation of nuclear factor of activated T cell was determined with gel mobility shift assay. The levels of HMGB1 in plasma were significantly elevated on PBDs 1 to 5. Significant proliferation of splenic T cells and IL-2, as well as IL-2Ralpha expression on T cells, were simultaneously suppressed to a certain extent on PBDs 1 to 7. Nuclear factor of activated T-cell activity of splenic T cells was markedly down-regulated on PBDs 1 to 3. Administration of ethyl pyruvate to inhibit HMGB1 can significantly restore proliferative activity, nuclear factor of activated T-cell activity, and expression levels of IL-2 and IL-2Ralpha on T cells. High-mobility group box 1 protein released after major burns might be associated with the pathogenesis of immunosuppression in splenic T lymphocytes in rats.

Induction of Bim and Bid gene expression during accelerated apoptosis in severe sepsis

Introduction

In transgenic animal models of sepsis, members of the Bcl-2 family of proteins regulate lymphocyte apoptosis and survival of sepsis. This study investigates the gene regulation of pro-apoptotic and anti-apoptotic members of the Bcl-2 family of proteins in patients with early stage severe sepsis.

Methods

In this prospective case-control study, patients were recruited from three intensive care units (ICUs) in a university hospital. Sixteen patients were enrolled when they fulfilled the criteria of severe sepsis. Ten critically ill but non-septic patients and 11 healthy volunteers served as controls. Blood samples were immediately obtained at inclusion. To confirm the presence of accelerated apoptosis in the patient groups, caspase-3 activation and phosphatidylserine externalisation in CD4+, CD8+ and CD19+ lymphocyte subsets were assessed using flow cytometry. Specific mRNAs of Bcl-2 family members were quantified from whole blood by real-time PCR. To test for statistical significance, Kruskal-Wallis testing with Dunn's multiple comparison test for post hoc analysis was performed.

Results

In all lymphocyte populations caspase-3 (p < 0.05) was activated, which was reflected in an increased phosphatidylserine externalisation (p < 0.05). Accordingly, lymphocyte counts were decreased in early severe sepsis. In CD4+ T-cells (p < 0.05) and B-cells (p < 0.001) the Bcl-2 protein was decreased in severe sepsis. Gene expression of the BH3-only Bim was massively upregulated as compared with critically ill patients (p < 0.001) and 51.6-fold as compared with healthy controls (p < 0.05). Bid was increased 12.9-fold compared with critically ill patients (p < 0.001). In the group of mitochondrial apoptosis inducers, Bak was upregulated 5.6-fold, while the expression of Bax showed no significant variations. By contrast, the pro-survival members Bcl-2 and Bcl-xl were both downregulated in severe sepsis (p < 0.001 and p < 0.05, respectively).

Conclusions

In early severe sepsis a gene expression pattern with induction of the pro-apoptotic Bcl-2 family members Bim, Bid and Bak and a downregulation of the anti-apoptotic Bcl-2 and Bcl-xl proteins was observed in peripheral blood. This constellation may affect cellular susceptibility to apoptosis and complex immune dysfunction in sepsis.

Involvement of CD45 in DNA fragmentation in apoptosis induced by mitochondrial perturbing agents

CD45 is a type I transmembrane molecule with phosphatase activity which comprises up to 10% of the cell surface area in nucleated haematopoietic cells. We have previously demonstrated the absence of nuclear apoptosis in CD45-negative T cells after chemical-induced apoptosis. The aim of this study was to characterize the role of CD45 in nuclear apoptosis. In contrast to wild type CD45-positive T cells, the CD45-deficient T cell lines are resistant to the induction of DNA fragmentation and chromatin condensation following tributyltin (TBT) or H2O2 exposure, but not to cycloheximide-induced apoptosis. CD45 transfection in deficient cell lines led to the restoration of chromatin condensation and DNA fragmentation following TBT exposure. In both CD45-positive and negative T cell lines, TBT exposure mediates intracellular calcium mobilization, caspase-3 activation and DFF45 cleavage. Moreover, DNA fragmentation was also induced by TBT in cells deficient in expression of p56lck, ZAP-70 and SHP-1. Subcellular partitioning showed a decrease in nuclear localisation of caspase-3 and DFF40. Together, these results demonstrate for the first time, that CD45 expression plays a key role in internucleosomal DNA fragmentation and chromatin condensation processes during apoptosis. CD45 activity or its substrates' activity, appears to be located downstream of caspase-3 activation and plays a role in retention of DFF40 in the nucleus.

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.

“Systemic apoptotic response” after thermal burns

The systemic pathophysiologic changes following thermal injuries affect multiple organs and body systems leading to clinical manifestations including shock, intestinal alterations, respiratory and renal failure, immunosuppression and others. Recent advances in the comprehension of mechanisms underlying systemic complications of thermal injuries have contributed to uncover part of the cellular and molecular basis that underlie such changes. Recently, programmed cell death (apoptosis) has been considered playing an important role in the development of such pathological events. Therefore, investigators utilizing animal models and clinical studies involving human primates have produced a large body of information suggesting that apoptosis is associated with most of the tissue damages triggered by severe thermal injuries. In order to draw the attention on the important role of apoptosis on systemic complications of thermal injuries, in this review we describe most of these studies, discuss possible cellular and molecular mechanisms and indicate ways to utilize them for the development of therapeutic strategies by which apoptosis may be prevented or counteracted.

The effect of burn injury on CD8+ and CD4+ T cells in an irradiation model of homeostatic proliferation

BACKGROUND

Homeostatic proliferation of T cells has recently been shown to be an important mechanism in the host response to infection. However, its role in the T cell response to burn injury is unknown. In this study, we examine the effect of burn injury on CD4+ and CD8+ T cell homeostatic proliferation after irradiation.

METHODS

Wild-type C57BL/6 female mice were irradiated with six grays ionizing radiation and 48 hours later, syngeneic whole splenocytes or purified CD4+ or CD8+ T cells labeled with carboxy-fluorescein diacetate, succinimidyl ester were adoptively transferred. Two days later, mice underwent a 20% burn injury, followed by splenocyte harvest 3 and 10 days after injury.

RESULTS

Burn mice demonstrate increased splenic cellularity and CD8+ T cell proliferation after adoptive transfer of either purified CD8+ cells or whole spleen populations compared with unburned (sham) mice. In contrast, CD4+ T cell proliferation after burn injury is unchanged after adoptive transfer of whole spleen cells and drastically decreased after adoptive transfer of a purified CD4+ population compared with sham mice. Ten days after burn injury CD8+ T cells continue to demonstrate greater proliferation than CD4+ T cells.

CONCLUSIONS

CD8+ T cells are more robust than CD4+ T cells in their proliferative response after burn injury. In addition, CD8+ T cell proliferation appears less reliant on other immune cells than purified CD4+ T cell proliferation. These data reiterate the importance of CD8+ T cells in the initial immune response to burn injury.

Immunologic responses to critical injury and sepsis

Almost 2 million patients are admitted to hospitals in the United States each year for treatment of traumatic injuries, and these patients are at increased risk of late infections and complications of systemic inflammation as a result of injury. Host response to injury involves a general activation of multiple systems in defending the organism from hemorrhagic or infectious death. Clinicians have the capability to support the critically injured through their traumatic insult with surgery and improved critical care, but the inflammatory response generated by such injuries creates new challenges in the management of these patients. It has long been known that local tissue injury induces systemic changes in the traumatized patient that are often maladaptive. This article reviews the effects of injury on the function of immune system cells and highlights some of the clinical sequelae of this deranged inflammatory-immune interaction.