Burn Injury Initiates a Shift in Superantigen-Induced T Cell Responses and Host Survival

VARIABLES INFLUENCING THE DIFFERENTIAL HOST RESPONSE TO BURNS IN PEDIATRIC AND ADULT PATIENTS

ABSTRACT

Burn injury is a significant source of morbidity and mortality in the pediatric population. Although 40,000 pediatric patients in the United States are admitted to the hospital with burn wounds annually, significant differences exist in the management and treatment of these patients, even among highly specialized burn centers. Some aspects of pediatric burn research, such as metabolic changes and nutritional support after burn injury, have been studied extensively; however, in many aspects of burn care, pediatric research lags behind the study of adult populations. This review compares and contrasts a wide array of physiologic and immune responses between children and adults after burn injury. Such a review elucidates where robust research has been conducted, where adult research is applicable to pediatric patients, and where additional pediatric burn research needs to be conducted.

The journey of SARS-CoV-2 in human hosts: a review of immune responses, immunosuppression, and their consequences

Coronavirus disease 2019 (COVID-19) is a highly infectious viral disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Laboratory findings from a significant number of patients with COVID-19 indicate the occurrence of leukocytopenia, specifically lymphocytopenia. Moreover, infected patients can experience contrasting outcomes depending on lymphocytopenia status. Patients with resolved lymphocytopenia are more likely to recover, whereas critically ill patients with signs of unresolved lymphocytopenia develop severe complications, sometimes culminating in death. Why immunodepression manifests in patients with COVID-19 remains unclear. Therefore, the evaluation of clinical symptoms and laboratory findings from infected patients is critical for understanding the disease course and its consequences. In this review, we take a logical approach to unravel the reasons for immunodepression in patients with COVID-19. Following the footprints of the virus within host tissues, from entry to exit, we extrapolate the mechanisms underlying the phenomenon of immunodepression.

Neurotransmitters and Neuropeptides decrease PD-1 in T cells of healthy subjects and patients with hepatocellular carcinoma (HCC), and increase their proliferation and eradication of HCC cells

T cells of aged people, and of patients with either cancer or severe infections (including COVID-19), are often exhausted, senescent and dysfunctional, leading to increased susceptibilities, complications and mortality. Neurotransmitters and Neuropeptides bind their receptors in T cells, and induce multiple beneficial T cell functions. Yet, T cells of different people vary in the expression levels of Neurotransmitter and Neuropeptide receptors, and in the magnitude of the corresponding effects. Therefore, we performed an individual-based study on T cells of 3 healthy subjects, and 3 Hepatocellular Carcinoma (HCC) patients. HCC usually develops due to chronic inflammation. The inflamed liver induces reduction and inhibition of CD4⁺ T cells and Natural Killer (NK) cells. Immune-based therapies for HCC are urgently needed. We tested if selected Neurotransmitters and Neuropeptides decrease the key checkpoint protein PD-1 in human T cells, and increase proliferation and killing of HCC cells. First, we confirmed human T cells express all dopamine receptors (DRs), and glutamate receptors (GluRs): AMPA-GluR3, NMDA-R and mGluR. Second, we discovered that either Dopamine, Glutamate, GnRH-II, Neuropeptide Y and/or CGRP (10nM), as well as DR and GluR agonists, induced the following effects: 1. Decreased significantly both %PD-1⁺ T cells and PD-1 expression level per cell (up to 60% decrease, within 1 h only); 2. Increased significantly the number of T cells that proliferated in the presence of HCC cells (up to 7 fold increase), 3. Increased significantly T cell killing of HCC cells (up to 2 fold increase). 4. Few non-conventional combinations of Neurotransmitters and Neuropeptides had surprising synergistic beneficial effects. We conclude that Dopamine, Glutamate, GnRH-II, Neuropeptide Y and CGRP, alone or in combinations, can decrease % PD-1⁺ T cells and PD-1 expression per cell, in T cells of both healthy subjects and HCC patients, and increase their proliferation in response to HCC cells and killing of HCC cells. Yet, testing T cells of many more cancer patients is absolutely needed. Based on these findings and previous ones, we designed a novel "Personalized Adoptive Neuro-Immunotherapy", calling for validation of safety and efficacy in clinical trials.

T Cells Plead for Rejuvenation and Amplification; With the Brain's Neurotransmitters and Neuropeptides We Can Make It Happen

T cells are essential for eradicating microorganisms and cancer and for tissue repair, have a pro-cognitive role in the brain, and limit Central Nervous System (CNS) inflammation and damage upon injury and infection. However, in aging, chronic infections, acute SARS-CoV-2 infection, cancer, chronic stress, depression and major injury/trauma, T cells are often scarce, exhausted, senescent, impaired/biased and dysfunctional. People with impaired/dysfunctional T cells are at high risk of infections, cancer, other diseases, and eventually mortality, and become multi-level burden on other people, organizations and societies. It is suggested that “Nerve-Driven Immunity” and “Personalized Adoptive Neuro-Immunotherapy” may overcome this problem. Natural Neurotransmitters and Neuropeptides: Glutamate, Dopamine, GnRH-II, CGRP, Neuropeptide Y, Somatostatin and others, bind their well-characterized receptors expressed on the cell surface of naïve/resting T cells and induce multiple direct, beneficial, and therapeutically relevant effects. These Neurotransmitters and Neuropeptides can induce/increase: gene expression, cytokine secretion, integrin-mediated adhesion, chemotactic migration, extravasation, proliferation, and killing of cancer. Moreover, we recently found that some of these Neurotransmitters and Neuropeptides also induce rapid and profound decrease of PD-1 in human T cells. By inducing these beneficial effects in naïve/resting T cells at different times after binding their receptors (i.e. NOT by single effect/mechanism/pathway), these Neurotransmitters and Neuropeptides by themselves can activate, rejuvenate, and improve T cells. “Personalized Adaptive Neuro-Immunotherapy” is a novel method for rejuvenating and improving T cells safely and potently by Neurotransmitters and Neuropeptides, consisting of personalized diagnostic and therapeutic protocols. The patient’s scarce and/or dysfunctional T cells are activated ex vivo once by pre-selected Neurotransmitters and/or Neuropeptides, tested, and re-inoculated to the patient’s body. Neuro-Immunotherapy can be actionable and repeated whenever needed, and allows other treatments. This adoptive Neuro-Immunotherapy calls for testing its safety and efficacy in clinical trials.

Scald Injury-Induced T Cell Dysfunction Can Be Mitigated by Gr1+ Cell Depletion and Blockage of CD47/CD172a Signaling

Infection is a common and severe complication of burn injury: Sepsis accounts for 47% of postburn mortality. Burn-induced T cell suppression likely contributes to the increased infection susceptibility in burn patients. However, little is known about the kinetics of T cell dysfunction after burn and its underlying mechanisms. In this study, we show in a murine scald injury model that T cell activation of both CD4⁺ and CD8⁺ T cells as well as T cell cytokine production is suppressed acutely and persistently for at least 11 days after burn injury. Purified T cells from scald-injured mice exhibit normal T cell functions, indicating an extrinsically mediated defect. We further show that T cell dysfunction after burn appears to be cell-to-cell contact dependent and can be ameliorated by depletion of myeloid-derived suppressor cells. These cells expand after burn injury, particularly a subset expressing the checkpoint inhibitor CD172a, and infiltrate germinal centers. Expression of CD172a appears to be driven by ingestion of immature reticulocytes. Immature reticulocytes are drastically increased in the spleen of scald mice and may contribute to immunosuppression through more direct mechanisms as well. Overall, our study newly identifies two cell populations, myeloid-derived suppressor cells and immature reticulocytes, as well as the CD47/CD172a-signaling pathways as mediators of T cell suppressors after burn and thus opens up new research opportunities in the search for new therapies to combat increased infection susceptibility and the associated morbidity and mortality in burn victims.

Long-lasting neurobehavioral alterations in burn-injured mice resembling post-traumatic stress disorder in humans

OBJECTIVE

To establish an animal model for posttraumatic stress disorder in burn-injured patients.

METHODS

Thermal-injured mice with 15% total body surface area were subjected to a series of neurobehavioral tests at 1 and 3 months postburn. Brains were collected for analysis of key molecules expression, spleens for T cell function analysis, and blood for biochemistry and hormones detection.

RESULTS

Comparison with sham mice, burn mice showed extremely high locomotion in homecage, open field, and forced swimming tests, indicating a hyper-arousal state. Burn mice exhibited improved spatial memory in Morris Water Maze test and heightened context fear memory in context fear conditioning, suggesting re-experiencing behavior. Although burn mice showed pronounced passive avoidance in the step-through test, their active avoidance capability in response to the conditional stimulus in the shuttle box test was relatively deteriorated. Likewise, the retention of cue-feared memory was impaired in fear conditioning test. The above negative alterations in mood were recapitulated in open-field test, in which the burn mice displayed an anxiety-like behavior with less time spent in the center. However, no sign of depression was found in the forced swimming and sucrose preference tests. The negative mood of burn mice was reinforced by a deficit in sociality and preference for social novelty in social interaction test. These neurobehavioral alterations were associated with an increased expression of brain-derived neurotrophic factor along with a remarkable microgliosis and a moderate astrocytosis in the brain of burn vs. sham mice. Moreover, a prominent Th2 switch and consequent increased nuclear NF-κB translocation were seen in the splenic T cells from burn relative to sham mice.

CONCLUSIONS

We conclude that even mild burn injury could lead to long-lasting cognitive and effective alterations in mice. These findings shed light on the interactions among neuropsychology, neurobiology, and immunology throughout the recovery period of burn injury.

Immune response to traumatic injury: harmony and discordance of immune system homeostasis

Trauma remains one of the leading causes of death worldwide. Traumatic injury disrupts immune system homeostasis and may predispose patients to opportunistic infections and inflammatory complications. Prevention of multiple organ dysfunction syndrome due to septic complications following severe trauma is a challenging problem. Following severe injury, the immune system usually tends toward a pro-inflammatory phenotype and then changes to a counter-inflammatory phenotype. This immune system homeostasis is believed to be a protective response based on the balance between the innate and adaptive immune systems. We reported that injury activates inflammasomes and primes Toll-like receptors. The primed innate immune system is prepared for a rapid and strong antimicrobial immune defense. However, trauma can also develop the "two-hit" response phenotype. We also reported that injury augments regulatory T cell activity, which can control the "two-hit" response phenotype in trauma. We discuss the current idea that traumatic injury induces a unique type of innate and adaptive immune response that may be triggered by damage-associated molecular pattern molecules, which are a combination of endogenous danger signal molecules that include alarmins and pathogen-associated molecular pattern molecules.

Trauma equals danger--damage control by the immune system

Traumatic injuries induce a complex host response that disrupts immune system homeostasis and predisposes patients to opportunistic infections and inflammatory complications. The response to injuries varies considerably by type and severity, as well as by individual variables, such as age, sex, and genetics. These variables make studying the impact of trauma on the immune system challenging. Nevertheless, advances have been made in understanding how injuries influence immune system function as well as the immune cells and pathways involved in regulating the response to injuries. This review provides an overview of current knowledge about how traumatic injuries affect immune system phenotype and function. We discuss the current ideas that traumatic injuries induce a unique type of a response that may be triggered by a combination of endogenous danger signals, including alarmins, DAMPs, self-antigens, and cytokines. Additionally, we review and propose strategies for redirecting injury responses to help restore immune system homeostasis.

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.

Effects of fluid resuscitation methods on the pro- and anti-inflammatory cytokines and expression of adhesion molecules after burn injury

Fluid resuscitation management can influence inflammatory response after burn injury. The aim of this study was to analyze the effects of two fluid resuscitation methods on the cytokine production and on the expression of the leukocyte surface markers. Thirty patients were included in this prospective randomized study with burn injury affecting more than 20% of the body surface area. Fluid resuscitation was guided by hourly urine output (HUO, n = 15) or by intrathoracic blood volume index (ITBVI, n = 15). Blood samples were taken on admission and on the next five consecutive mornings. Concentrations of interleukin (IL)-1beta, IL-6, IL-8, IL-10, IL-12p70, and tumor necrosis factor-alpha were measured in phorbol myristate acetate-stimulated and -nonstimulated samples. Leukocyte surface marker expressions (CD11a, CD11b, CD14, CD18, CD49d, and CD97) were also determined. In the ITBVI group, IL-6 levels on days 2 to 3 and IL-6/IL-10 ratios on days 2 to 3, and the IL-8/IL-10 ratios on days 3 to 5 were significantly higher than those in HUO group (P < .05). In the HUO group, IL-10 levels were significantly higher (P < .05) on days 4 and 5. Granulocyte CD11a levels on day 2, CD11b levels on days 4 to 6, lymphocyte CD11a on days 5 to 6, CD11b on days 3 to 6, CD49d on days 2 to 6, CD97 on day 6, monocyte CD11a, CD11b, CD18 levels on days 4 to 6, and CD14 levels on days 3 to 5 were significantly higher in the HUO group (P < .05). Our study suggests that ITBVI-guided fluid resuscitation of burned patients suppresses the shift toward anti-inflammatory imbalance and the expression of leukocyte surface markers more than HUO-guided resuscitation.

Burn trauma induces early HMGB1 release in patients: its correlation with cytokines

High-mobility group box protein 1 (HMGB1) is a nuclear protein that may be released actively from monocytes and macrophages or passively from necrotic or damaged cells. Several experimental data suggest that burn injury is accompanied by elevated plasma HMGB, but there are only few data available about its changes in burned patients. The aim of this study was to follow the time course and the prognostic value of plasma HMGB1 and cytokine changes in patients with severe burn injury affecting more than 10% of body surface area (n = 26). Blood samples were taken on admission and on the following 5 days. Plasma HMGB1 concentration was measured by the enzyme-linked immunosorbent assay method, whereas IL-6, IL-8, and IL-10 were assayed by the cytometric bead array kit. The HMGB1 and IL-10 concentrations were elevated on admission and gradually decreased thereafter. Significant differences were observed between survivors and nonsurvivors in HMGB1 (P < 0.01) and IL-10 (P < 0.001) concentrations on admission with higher levels in nonsurvivors. IL-6 and IL-8 started to increase markedly from day 2. Positive correlation (r = 0.669, P < 0.01) was found between burned body surface and HMGB1 on admission. Receiver operating characteristic analysis of data on admission showed that at a level of 16 ng/mL, HMGB1 indicated lethality, with 75.0% sensitivity and 85.7% specificity. Using the cutoff level of 14 pg/mL, IL-10 predicted intensive care unit mortality, with 85.7% sensitivity and 84.2% specificity. Very early HMGB1 and IL-10 release may have an important impact on the immune function of patients after burn trauma.

Burn injury induces the expression of cystine/glutamate transporter (x(c)(-)) in mouse T cells

System x(c)(-) transporter, formed by the association of CD98 and xCT proteins, regulates the import of cystine into cells and is poorly expressed in T lymphocytes. Thermal injury is associated with high oxidative stress, decreased levels of glutathione (GSH) and protein deficiency, all described as promoters of xCT expression and system x(c)(-) activity. T cell dysfunction is a consequence of thermal injury and has been related to oxidative stress. In order to evaluate if thermal injury induced system x(c)(-) expression in splenic T lymphocytes, cells were isolated from sham- and burn-injured mice at day 10 post-burn and cultured in 2-mercaptoethanol (2-ME)-rich and -free media. Isolated splenic T cells were stimulated and cell proliferation, system x(c)(-) expression and cystine transport activity were measured. Our results demonstrate that only burn-injured T cells express xCT and proliferate in (2-ME)-free media. In these cells, viability and CD25 expression was higher than control T cells. x(c)(-) system expression was responsible for significantly higher (14)C-cystine uptake by burn-injured T cells and its inhibition by sulfasalazine (SASP) decreased significantly their proliferation. Overall, these results demonstrate that xCT expression is induced by thermal injury in T lymphocytes and that cystine import by x(c)(-) leads to T cell dysfunction.

Murine dendritic cell antigen-presenting cell function is not altered by burn injury

Severe injury disrupts normal immune regulation causing a transient hyperinflammatory reaction and suppressed adaptive immune function. This report addresses the potential contribution of dendritic cells (DC) to changes in adaptive immune function after injury by specifically measuring injury-induced changes in splenic DC numbers and subsets, cell-surface markers, TLR responses, and APC function. Using a mouse burn injury model, we found that injury did not markedly alter the relative percentage of lymphoid, myeloid, or plasmacytoid DC in the spleens of burn-injured mice. Moreover, we did not observe a significant reduction in cell-surface expression of several major costimulatory molecules, CD40, CD80, CD86, programmed death 1 ligand, ICOS ligand, and B7-H3, on DC. Instead, we observed increased cell-surface expression of CD86 at 1 day after injury with no significant changes in costimulatory molecule expression at 7 days after injury, suggesting that burn injury causes an early activation of DC. In addition, injury did not suppress DC reactivity to TLR2, TLR4, or TLR9 agonists. Most important, DC prepared from injured mice were able to present peptide antigen to naive OTII TCR transgenic CD4+ T cells as efficiently and effectively as DC from sham-injured mice. We also found that CD4 T cells stimulated with antigen presented by DC from sham or burn mice showed similar levels of IL-2, IFN-gamma, IL-10, and IL-13 production. Taken together, these findings support the conclusion that DC do not acquire a suppressive phenotype following severe injury in mice.

Phenotype of CD4+ T cell subsets that develop following mouse facial nerve axotomy

We have previously shown that CD4(+) T helper (Th) 2 cells, but not Th1 cells, participate in the rescue of mouse facial motoneurons (FMN) from axotomy-induced cell death. Recently, a number of other CD4(+) T cell subsets have been identified in addition to the Th1 and Th2 effector subsets, including Th17, inducible T regulatory type 1 (Tr1), and naturally thymus-born Foxp3(+) regulatory (Foxp3(+) Treg) cells. These subsets regulate the nature of a T cell-mediated immune response. Th1 and Th17 cells are pro-inflammatory subsets, while Th2, Tr1, and Foxp3(+) Treg cells are anti-inflammatory subsets. Pro-inflammatory responses in the central nervous system are thought to be neurodestructive, while anti-inflammatory responses are considered neuroprotective. However, it remains to be determined if another CD4(+) T cell subset, other than the Th2 cell, develops after peripheral nerve injury and participates in FMN survival. In the present study, we used FACS analysis to determine the temporal frequency of Th1, Th17, Th2, Tr1 and Foxp3(+) Treg CD4(+) T cell subset development in C57BL/6 wild type mice after facial nerve transection at the stylomastoid foramen in the mouse. The results indicate that all of the known CD4(+) T cell subsets develop and expand in number within the draining lymph node, with a peak in number primarily at 7 days postoperative (dpo), followed by a decline at 9 dpo. In addition to the increase in subset frequency over time, FACS analysis of individual cells showed that the level of cytokine expressed per cell also increased for interferon-gamma (IFN-gamma), interleukin (IL)-10 and IL-17, but not IL-4. Additional control double-cytokine labeling experiments were done which indicate that, at 7dpo, the majority of cells indeed have committed to a specific phenotype and express only 1 cytokine. Collectively, our findings indicate for the first time that there is no preferential activation and expansion of any single CD4(+) T cell subset after peripheral nerve injury but, rather, that both pro-inflammatory and anti-inflammatory CD4(+) T cells develop.

CD4+ T-cell depletion is not associated with alterations in survival, bacterial clearance, and inflammation after cecal ligation and puncture

Our recent studies indicate that mice depleted of T cells that bear the alphabeta T-cell receptor (alphabeta T cells) show less inflammation, less physiological dysfunction, and improved survival after cecal ligation and puncture (CLP) compared with control mice. Classic CD4(+) and CD8(+) T cells comprise most of the alphabeta T-cell population. We previously showed that CD8(+) T cells, in conjunction with natural killer (NK) cells, participate in CLP-induced inflammation. However, the contribution of CD4(+) T cells to the early inflammatory response caused by CLP is largely undefined. In the present study, we evaluated CLP-induced mortality, bacterial clearance, and inflammation in mice that were depleted of CD4(+) T cells. Compared with control mice, CD4 knockout mice and wild-type mice treated with anti-CD4 did not show significant differences in survival, cytokine production, and systemic bacterial counts. The combined depletion of CD4(+) T and NK cells resulted in improved survival and decreased cytokine production compared with mice possessing a full lymphocyte complement, especially when CD4(+) T and NK cell-deficient mice were treated with imipenem. These improvements were nearly identical to those observed in mice depleted only of NK cells. These studies show that CD4(+) T cells do not seem to play a critical role in facilitating the early inflammatory response caused by CLP.

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.

Mice depleted of alphabeta but not gammadelta T cells are resistant to mortality caused by cecal ligation and puncture

The present study was undertaken to determine whether the mice depleted of alphabeta or gammadelta T cells show resistance to acute polymicrobial sepsis caused by cecal ligation and puncture (CLP). T-cell receptor beta knockout (betaTCRKO) and T-cell receptor delta knockout (deltaTCRKO) mice were used. An additional group of mice was treated with an antibody against the alphabeta T-cell receptor to induce alphabeta T-cell depletion; a subset of alphabeta T cell-deficient mice was also treated with anti-asialoGM1 to deplete natural killer (NK) cells. The mice underwent CLP and were monitored for survival, temperature, acid-base balance, bacterial counts, and cytokine production. The betaTCRKO mice and the wild-type mice treated with anti-beta T-cell receptor (anti-TCRbeta) antibody showed improved survival after CLP compared with wild-type mice. The treatment of alphabeta T cell-deficient mice with anti-asialoGM1further improved survival after CLP, especially when the mice were treated with imipenem. The improved survival observed in alphabeta T cell-deficient mice was associated with less hypothermia, improved acid-base balance, and decreased production of the proinflammatory cytokines interleukin (IL) 6 and macrophage inflammatory protein (MIP) 2. Compared with wild-type controls, the overall survival was not improved in deltaTCRKO mice. The concentrations of IL-6 and MIP-2 in plasma and cytokine mRNA expression in tissues were not significantly different between wild-type and deltaTCRKO mice. These studies indicate that mice depleted of alphabeta but not of gammadelta T cells are resistant to mortality in an acutely lethal model of CLP. The depletion of NK cells caused further survival benefit in alphabeta T cell-deficient mice. These findings suggest that alphabeta T and NK cells mediate or facilitate CLP-induced inflammatory 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.

Injury-induced suppression of effector T cell immunity requires CD1d-positive APCs and CD1d-restricted NKT cells

Overwhelming infection remains the leading cause of death from serious burn injury despite recent advances in the care of burn patients and a better understanding of immune and inflammatory consequences of injury. In this study, we report a critical requirement for CD1d-restricted NKT cells and CD1d expression by APCs in the immune dysfunction that occurs early after burn injury. Using a well-established murine scald injury model with BALB/c and BALB/c CD1d knockout mice, we investigated whether peripheral T cell immunity was affected by the presence or absence of CD1d-restricted NKT cells in the early stages after injury. Using Ag-specific delayed-type hypersensitivity, T cell proliferation, and cytokine production as indices of immune responsiveness, we observed that both CD1d expression by APCs and CD1d-restricted NKT cells are required for immune suppression after injury. Via adoptive transfer of splenocytes from injured mice to uninjured recipients, we found injury-induced suppression of immunity to be Ag specific, long lasting, and critically dependent on cell surface expression of CD1d by APCs. Together, our results suggest that the defects in T cell responsiveness that occur subsequent to severe burn injury are not merely the result of global or passive suppression, but instead represent an active form of CD1d/NKT cell-dependent immunologic tolerance.

Lymphopenia-Induced Homeostatic Proliferation of CD8+T Cells Is a Mechanism for Effective Allogeneic Skin Graft Rejection following Burn Injury

Burn patients are immunocompromised yet paradoxically are able to effectively reject allogeneic skin grafts. Failure to close a massive burn wound leads to sepsis and multiple system organ failure. Immune suppression early (3 days) after burn injury is associated with glucocorticoid-mediated T cell apoptosis and anti-inflammatory cytokine responses. Using a mouse model of burn injury, we show CD8+ T cell hyperresponsiveness late (14 days) after burn injury. This is associated with a CD8+ T cell pro- and anti-inflammatory cytokine secretion profile, peripheral lymphopenia, and accumulation of a rapidly cycling, hyperresponsive memory-like CD8+CD44+ IL-7R- T cells which do not require costimulation for effective Ag response. Adoptive transfer of allospecific CD8+ T cells purified 14 days postburn results in enhanced allogeneic skin graft rejection in unburned recipient mice. Chemical blockade of glucocorticoid-induced lymphocyte apoptosis early after burn injury abolishes both the late homeostatic accumulation of CD8+ memory-like T cells and the associated enhanced proinflammatory CD8+ T cell response, but not the late enhanced CD8+ anti-inflammatory response. These data suggest a mechanism for the dynamic CD8+ T cell response following injury involving an interaction between activation, apoptosis, and cellular regeneration with broad clinical implications for allogeneic skin grafting and sepsis.

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.

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.

Hypertonic saline dextran after burn injury decreases inflammatory cytokine responses to subsequent pneumonia-related sepsis

The present study examined the hypothesis that hypertonic saline dextran (HSD), given after an initial insult, attenuates exaggerated inflammation that occurs with a second insult. Adult rats (n = 15 per group) were divided into groups 1 (sham burn), 2 [40% total body surface area burn + 4 ml/kg isotonic saline (IS) + 4 ml.kg(-1).% burn(-1) lactated Ringer solution (LR)], and 3 (burn + 4 ml/kg HSD + LR), all studied 24 h after burns. Groups 4 (sham burn), 5 (burn + IS + LR), and 6 (burns + HSD + LR) received intratracheal (IT) vehicle 7 days after burns; groups 7 (burn + IS + LR) and 8 (burn + HSD + LR) received IT Streptococcus pneumoniae (4 x 10(6) colony-forming units) 7 days after burn. Groups 4-8 were studied 8 days after burn and 24 h after IT septic challenge. When compared with sham burn, contractile defects occurred 24 h after burn in IS-treated but not HSD-treated burns. Cardiac inflammatory responses (pg/ml TNF-alpha) were evident with IS (170 +/- 10) but not HSD (45 +/- 5) treatment vs. sham treatment (80 +/- 15). Pneumonia-related sepsis 8 days after IS-treated burns (group 7) exacerbated TNF-alpha responses/contractile dysfunction vs. IS-treated burns in the absence of sepsis (P < 0.05). Sepsis that occurred after HSD-treated burns (group 8) had less myocyte TNF-alpha secretion/better contractile function than IS-treated burns given septic challenge (group 7, P < 0.05). We conclude that an initial burn injury exacerbates myocardial inflammation/dysfunction occurring with a second insult; giving HSD after the initial insult attenuates myocardial inflammation/dysfunction associated with a second hit, suggesting that HSD reduces postinjury risk for infectious complications.

Antigen presenting cells (APCs) from thermally injured and/or septic rats modulate CD4+ T cell responses of naive rat

Regulation of immune response is marked by complex interactions among the cells that recognize and present antigens. Antigen presenting cells (APCs), the antigen presenting cell component of the innate immune response plays an important role in effector CD4+ T cell response. Thermal injury and/or superimposed sepsis in rats' leads to suppressed CD4+ T cell functions. We investigated modulations of CD4+ T cell function by APCs (purified non-T cells) from thermally injured and/or septic rats. Rats were subjected to 30% total body surface area scald burn or exposed to 37 degrees C water (Sham burn) and sepsis was induced by cecal-ligation and puncture (CLP) method. At day 3 post-injury animals were sacrificed and CD4+ T cells and APCs from mesenteric lymph nodes (MLN) were obtained using magnetic microbead isolation procedure. APCs from injured rats were co-cultured with sham rat MLN CD4+ T cells and proliferative responses (thymidine incorporation), phenotypic changes (Flow cytometry), IL-2 production (ELISA) and CTLA-4 mRNA (RT-PCR) were determined in naive rat CD4+ T cells. The data indicate that APCs from thermally injured and/or septic rats when co-cultured with CD4+ T cells suppressed CD4+ T cell effector functions. This lack of CD4+ T cell activation was accompanied with altered co-stimulatory molecules, i.e., CD28 and/or CTLA-4 (CD152). In conclusion, our studies indicated that defective APCs from thermally injured and/or septic rats modulate CD4+ T cell functions via changes in co-stimulatory molecules expressed on naive CD4+ T cells. This altered APC: CD4+ T cell interaction leads to suppressed CD4+ T cell activation of healthy animals.

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

Burn injuries are known to be associated with altered immune functions, resulting in decreased resistance to subsequent infection. In the present study, we determined the in vivo changes in T cell homeostasis following burn injury. Two groups of mice were used: a sham-burn group receiving buprenorphine as an analgesic and a burn group receiving buprenorphine and subjected to burn injury on 20% of the total body surface area. Results showed an important decrease in splenocytes following burn injury. This decrease persisted for 5 days and was followed, at day 10, by a 63% increase in number of cells. In vivo cell proliferation, as determined by the incorporation of 5-bromo-2'-dexoxyuridine, showed a significant increase of cycling splenocytes between days 2 and 10 after burn injury. The percentage of CD4+ and CD8+ T cells in the spleen was altered for 10 days after thermal injury. Analysis of naive (CD62Lhigh CD44low) and effector/memory (CD62Llow CD44high) T cells showed a percent decrease, independent of the expression of CD4 or CD8 molecules. However, early activation markers, such as CD69+, were expressed only on CD4+ T cells after a number of days following injury. Even with an activated phenotype, 10 days post-burn injury, CD4+ naive T cells significantly increased spontaneous apoptosis, detected by using a fluorescent DNA-binding agent 7-amino-actinomycin D. CD8+ T lymphocytes did not express early activation markers and were more resistant to apoptosis. Using purified T cells, we have shown unresponsiveness at day 10. Overall, these results demonstrate that mechanisms of T cell homeostasis were perturbed following burn injury. However, after 10 days, this perturbation persisted only in CD4+ T cells.