Late immune consequences of combat trauma: a review of trauma-related immune dysfunction and potential therapies

Optimization of a Lethal, Combat-Relevant Model of Sterile Inflammation in Mice for Drug Candidate Screening

INTRODUCTION

Extensive trauma, commonly seen in wounded military Service Members, often leads to a severe sterile inflammation termed systemic inflammatory response syndrome (SIRS), which can progress to multiple organ dysfunction syndrome (MODS) and death. MODS is a serious threat to wounded Service Members, historically causing 10% of all deaths in trauma admissions at a forward deployed combat hospital. The importance of this problem will be exacerbated in large-scale combat operations, in which evacuation will be delayed and care of complex injuries at lower echelons of care may be prolonged. The main goal of this study was to optimize an existing mouse model of lethal SIRS/MODS as a therapeutic screening platform for the evaluation of immunomodulatory drugs.

MATERIALS AND METHODS

Male C57BL/6 mice were euthanized, and the bones and muscles were collected and blended into a paste termed tissue-bone matrix (TBX). The TBX at 12.5%-20% relative to body weight of each recipient mouse was implanted into subcutaneous pouches created on the dorsum of anesthetized animals. Mice were observed for clinical scores for up to 48 hours postimplantation and euthanized at the preset point of moribundity. To test effects of anesthetics on TBX-induced mortality, animals received isoflurane or ketamine/xylazine (K/X). In a separate set of studies, mice received TBX followed by intraperitoneal injection with 20 mg/kg or 40 mg/kg Eritoran or a placebo carrier. All Eritoran studies were performed in a blinded fashion.

RESULTS

We observed that K/X anesthesia significantly increased the lethality of the implanted TBX in comparison to inhaled anesthetics. Although all the mice anesthetized with isoflurane and implanted with 12.5% TBX survived for 24 hours, 60% of mice anesthetized with K/X were moribund by 24 hours postimplantation. To mimic more closely the timing of lethal SIRS/MODS following polytrauma in human patients, we extended observation to 48 hours. We performed TBX dose-response studies and found that as low as 15%, 17.5%, and 20% TBX caused moribundity/mortality in 50%, 80%, and 100% mice, respectively, over a 48-hour time period. With 17.5% TBX, we tested if moribundity/mortality could be rescued by anti-inflammatory drug Eritoran, a toll-like receptor 4 antagonist. Neither 20 mg/kg nor 40 mg/kg doses of Eritoran were found to be effective in this model.

CONCLUSIONS

We optimized a TBX mouse model of SIRS/MODS for the purpose of evaluating novel therapeutic interventions to prevent trauma-related pathophysiologies in wounded Service Members. Negative effects of K/X on lethality of TBX should be further evaluated, particularly in the light of widespread use of ketamine in treatment of pain. By mimicking muscle crush, bone fracture, and necrosis, the TBX model has pleiotropic effects on physiology and immunology that make it uniquely valuable as a screening tool for the evaluation of novel therapeutics against trauma-induced SIRS/MODS.

Optimization and Validation of an FTIR-based, All-in-one System for Viable MDR Bacteria Detection in Combat-related Wound Infection

INTRODUCTION

The U.S. Military members experiencing combat-related injuries have a higher chance of developing infections by multidrug-resistant (MDR) bacteria at admission to military hospitals. MDR wound infections result in higher amputation rates and greater risks for subsequent or chronic infections that require readmission or extended stay in the hospital. Currently, there is no FDA-clear, deployable early diagnostic system for suitable field use.We are reporting our efforts to improve a previously developed Rapid Label-free Pathogen Identification (RAPID) system to detect viable MDR bacteria in wound infections and perform antibiotic susceptibility testing (AST). Specifically, we added multiplex and automation capability and significantly simplified the sample preparation process. A functional prototype of the improved system was built, and its performance was validated using a variety of lab-prepared spiked samples and real-world samples.

MATERIALS AND METHODS

To access the baseline performance of the improved RAPID system in detecting bacteria presence, we selected 17 isolates, most of them from blood or wound infections, and prepared mono-strain spiked samples at 104 to 106 cfu/mL concentration. These samples were processed and analyzed by the RAPID system. To demonstrate the AST capability of the system, we selected 6 strains against 6 different antibiotics and compared the results from the system with the ones from the gold standard method.To validate the system's performance with real-world samples, we first investigated its performance on 3 swab samples from epicutaneous methicillin-resistant Staphylococcus aureus-exposed mouse model. The AST results from our system were compared with the ones from the gold standard method. All animal experiments were approved by the Johns Hopkins University Animal Care and Use Committee (Protocol No. MO21M378). Then, we obtained swab samples from 7 atopic dermatitis (AD) patients and compared our AST results with the ones from the gold standard method. The human subject protocol was approved by the Johns Hopkins Medicines Institutional Review Boards (Study No. CR00043438/IRB00307926) and by USAMRDC (Proposal Log Number/Study Number 20000251).

RESULTS

High-quality data were obtained from the spiked samples of all 17 strains. A quantitative analysis model built using these data achieved 94% accuracy in predicting the species ID in 8 unknown samples. The AST results on the spiked samples had shown 100% matching with the gold standard method. Our system successfully detects the presence/absence of viable bacteria in all 3 mouse and 7 AD patient swab samples. Our system shows 100% and 85.7% (6 out of 7) accuracy when compared to the oxacillin susceptibility testing results for the mouse and the AD patient swabs, respectively.

CONCLUSIONS

Our system has achieved excellent performance in detecting viable bacteria presence and in performing AST in a multiplex, automated, and easy-to-operate manner, on both lab-prepared and real samples. Our results have shown a path forward to a rapid (sample-to-answer time ≤3 hours), accurate, sensitive, species-specific, and portable system to detect the presence of MDR combat-related wound infections in the field environment. Our future efforts involve ruggedizing the RAPID system and evaluating performance under relevant environmental conditions.

Inhibition of focal adhesion kinase 2 results in a macrophage polarization shift to M2 which attenuates local and systemic inflammation and reduces heterotopic ossification after polysystem extremity trauma

Introduction

Heterotopic ossification (HO) is a complex pathology often observed in combat injured casualties who have sustained severe, high energy polytraumatic extremity injuries. Once HO has developed, prophylactic therapies are limited outside of surgical excision. Tourniquet-induced ischemia injury (IR) exacerbates trauma-mediated musculoskeletal tissue injury, inflammation, osteogenic progenitor cell development and HO formation. Others have shown that focal adhesion kinase-2 (FAK2) plays a key role in regulating early inflammatory signaling events. Therefore, we hypothesized that targeting FAK2 prophylactically would mitigate extremity trauma induced IR inflammation and HO formation.

Methods

We tested whether the continuous infusion of a FAK2 inhibitor (Defactinib, PF-573228; 6.94 µg/kg/min for 14 days) can mitigate ectopic bone formation (HO) using an established blast-related extremity injury model involving femoral fracture, quadriceps crush injury, three hours of tourniquet-induced limb ischemia, and hindlimb amputation through the fracture site. Tissue inflammation, infiltrating cells, osteogenic progenitor cell content were assessed at POD-7. Micro-computed tomography imaging was used to quantify mature HO at POD-56.

Results

In comparison to vehicle control-treated rats, FAK2 administration resulted in no marked wound healing complications or weight loss. FAK2 treatment decreased HO by 43%. At POD-7, marked reductions in tissue proinflammatory gene expression and assayable osteogenic progenitor cells were measured, albeit no significant changes in expression patterns of angiogenic, chondrogenic and osteogenic genes. At the same timepoint, injured tissue from FAK-treated rats had fewer infiltrating cells. Additionally, gene expression analyses of tissue infiltrating cells resulted in a more measurable shift from an M1 inflammatory to an M2 anti-inflammatory macrophage phenotype in the FAK2 inhibitor-treated group.

Discussion

Our findings suggest that FAK2 inhibition may be a novel strategy to dampen trauma-induced inflammation and attenuate HO in patients at high risk as a consequence of severe musculoskeletal polytrauma.

During Sepsis and COVID-19, the Pro-Inflammatory and Anti-Inflammatory Responses Are Concomitant

The most severe forms of COVID-19 share many features with bacterial sepsis and have thus been considered to be a viral sepsis. Innate immunity and inflammation are closely linked. While the immune response aims to get rid of the infectious agent, the pro-inflammatory host response can result in organ injury including acute respiratory distress syndrome. On its side, a compensatory anti-inflammatory response, aimed to dampen the inflammatory reaction, can lead to immunosuppression. Whether these two key events of the host inflammatory response are consecutive or concomitant has been regularly depicted in schemes. Initially proposed from 2001 to 2013 to be two consecutive steps, the concomitant occurrence has been supported since 2013, although it was proposed for the first time in 2001. Despite a consensus was reached, the two consecutive steps were still recently proposed for COVID-19. We discuss why the concomitance view could have been initiated as early as 1995.

Mycelium-based biomaterials as smart devices for skin wound healing

Introduction: Recently, mycelia of Ganoderma lucidum and Pleurotus ostreatus, edible fungi, have been characterized in vitro as self-growing biomaterials for tissue engineering since they are constituted of interconnected fibrous networks resembling the dermal collagen structure. Aim: This work aims to investigate the biopharmaceutical properties of G. lucidum and P. ostreatus mycelia to prove their safety and effectiveness in tissue engineering as dermal substitutes. Methods: The mycelial materials were characterized using a multidisciplinary approach, including physicochemical properties (morphology, thermal behavior, surface charge, and isoelectric point). Moreover, preclinical properties such as gene expression and in vitro wound healing assay have been evaluated using fibroblasts. Finally, these naturally-grown substrates were applied in vivo using a murine burn/excisional wound model. Conclusions: Both G. lucidum and P. ostreatus mycelia are biocompatible and able to safely and effectively enhance tissue repair in vivo in our preclinical model.

Circulatory HMGB1 is an early predictive and prognostic biomarker of ARDS and mortality in a swine model of polytrauma

Acute respiratory distress syndrome (ARDS) is a leading cause of morbidity and mortality in polytrauma patients. Pharmacological treatments of ARDS are lacking, and ARDS patients rely on supportive care. Accurate diagnosis of ARDS is vital for early intervention and improved outcomes but is presently delayed up to days. The use of biomarkers for early identification of ARDS development is a potential solution. Inflammatory mediators high-mobility group box 1 (HMGB1), syndecan-1 (SDC-1), and C3a have been previously proposed as potential biomarkers. For this study, we analyzed these biomarkers in animals undergoing smoke inhalation and 40% total body surface area burns, followed by intensive care for 72 h post-injury (PI) to determine their association with ARDS and mortality. We found that the levels of inflammatory mediators in serum were affected, as well as the degree of HMGB1 and Toll-like receptor 4 (TLR4) signal activation in the lung. The results showed significantly increased HMGB1 expression levels in animals that developed ARDS compared with those that did not. Receiver operating characteristic (ROC) analysis showed that HMGB1 levels at 6 h PI were significantly associated with ARDS development (AUROC=0.77) and mortality (AUROC=0.82). Logistic regression analysis revealed that levels of HMGB1 ≥24.10 ng/ml are associated with a 13-fold higher incidence of ARDS [OR:13.57 (2.76-104.3)], whereas the levels of HMGB1 ≥31.39 ng/ml are associated with a 12-fold increase in mortality [OR: 12.00 (2.36-93.47)]. In addition, we found that mesenchymal stem cell (MSC) therapeutic treatment led to a significant decrease in systemic HMGB1 elevation but failed to block SDC-1 and C3a increases. Immunohistochemistry analyses showed that smoke inhalation and burn injury induced the expression of HMGB1 and TLR4 and stimulated co-localization of HMGB1 and TLR4 in the lung. Interestingly, MSC treatment reduced the presence of HMGB1, TLR4, and the HMGB1-TLR4 co-localization. These results show that serum HMGB1 is a prognostic biomarker for predicting the incidence of ARDS and mortality in swine with smoke inhalation and burn injury. Therapeutically blocking HMGB1 signal activation might be an effective approach for attenuating ARDS development in combat casualties or civilian patients.

Adjunctive hemoperfusion with Resin Hemoadsorption (HA) 330 cartridges improves outcomes in patients sustaining multiple Blunt Trauma: a prospective, quasi-experimental study

BACKGROUND

Multi-organ dysfunction syndrome and multi-organ failure are the leading causes of late death in patients sustaining severe blunt trauma. So far, there is no established protocol to mitigate these sequelae. This study assessed the effect of hemoperfusion using resin-hemoadsorption 330 (HA330) cartridges on mortality and complications such as acute respiratory distress syndrome (ARDS) and systemic inflammatory response syndrome (SIRS) among such patients.

METHODS

This quasi-experimental study recruited patients ≥ 15 years of age with blunt trauma, injury severity score (ISS) ≥ 15, or initial clinical presentation consistent with SIRS. They were divided into two groups: the Control group received only conventional acute care, while the case group received adjunctive hemoperfusion. P-values less than 0.05 were statistically significant.

RESULTS

Twenty-five patients were included (Control and Case groups: 13 and 12 patients). The presenting vital signs, demographic and injury-related features (except for thoracic injury severity) were similar (p > 0.05). The Case group experienced significantly more severe thoracic injuries than the Control group (Thoracic AIS, median [IQR]: 3 [2-4] vs. 2 [0-2], p = 0.01). Eleven and twelve patients in the Case group had ARDS and SIRS before the hemoperfusion, respectively, and these complications were decreased considerably after hemoperfusion. Meanwhile, the frequency of ARDS and SIRS did not decrease in the Control group. Hemoperfusion significantly reduced the mortality rate in the Case group compared to the Control group (three vs. nine patients, p = 0.027).

CONCLUSIONS

Adjunctive Hemoperfusion using an HA330 cartridge decreases morbidity and improves outcomes in patients suffering from severe blunt trauma.

Dynamics of immune responses are inconsistent when trauma patients are grouped by injury severity score and clinical outcomes

The injury severity score (ISS) is used in daily practice to evaluate the severity of trauma patients; however, the score is not always consistent with the prognosis. After injury, systemic inflammatory response syndrome (SIRS) and compensatory anti-inflammatory response syndrome (CARS) are related to the prognosis of trauma patients. We aimed to evaluate the associations between the immune response and prognosis in trauma patients. Patients who admitted to the Trauma Intensive Care Unit (ICU) were eligible. Whole blood samples were collected at admission, and then 6, 12, 24, 48 and 72 h after admission. Natural killer (NK) cells, lymphocyte subset population and cytokines release were identified using flow cytometry. We grouped patients by their ISS (≤ 25 and > 25 as very severe injury) and ICU stay (≤ 10 days as a short ICU stay and > 10 days as a long ICU stay) for evaluation. Fifty-three patients were enrolled. ICU stay but not ISS was close correlated with activity daily living (ADL) at discharge. Patients with a long ICU stay had an immediate increase in NK cells followed by lymphopenia which persisted for 48 h. Immediate activation of CD8⁺ T cells and then exhaustion with a higher programmed cell death-1 (PD-1) expression and suppression of CD4⁺ T cells with a shift to an anti-inflammatory Th2 phenotype were also observed in the patients with a long ICU stay. When the patients were grouped by ISS, the dynamics of immune responses were inconsistent to those when the patients were grouped by ICU stay. Immune responses are associated with the prognosis of trauma patients, however the currently used clinical parameters may not accurately reflect immune responses. Further investigations are needed to identify accurate predictors of prognosis in trauma patients.

Educational inequalities in heart failure mortality and the cycles of the internal armed conflict in Colombia: An observational panel study of ecological data, 1999-2017

Heart failure (HF) is a significant clinical problem and an important public health issue due to the morbidity and mortality that it causes, especially in a population that is aging and affected by social stressors such as armed conflict. We aim to describe the inequalities and trends of HF mortality by educational level in Colombia between 1999 and 2017 compared with the cycles of the internal armed conflict during the same period. An observational study of ecological data panels, with aggregates at the national level, was conducted. Information from death certificates with HF as the basic cause of death (COD) was used. Variables of the year of death, sex, age, department of residence, and educational level were considered. Mortality rates adjusted for age were calculated. A joinpoint regression was used to model the trend of rates by educational level. We found that both men and women with primary education had the highest adjusted mortality rates: among men, RR_primary = 19.06 deaths/100,000 inhabitants, SE = 0.13 vs. RR_tertiary = 4.85, SE = 0.17, and similar differences among women. Mortality rates tended to decrease at all educational levels, with a greater reduction in people with higher educational levels. In both sexes, the behavior of the relative index of inequality showed significant inequality, albeit with a strong reduction during the last decade. Mortality due to HF in Colombia shows inequalities by educational level. In the prevention of HF, education should be considered a structural social determinant. In addition, we analyzed the potential role of the Colombian long-term armed conflict in the observed trends. We highlighted the role of the health sector, together with other sectors (education, work, and housing), in developing intersectoral public policies that contribute to the reduction of cardiovascular mortality disparities.

Danger signals in traumatic hemorrhagic shock and new lines for clinical applications

Hemorrhage is the leading cause of death in severe trauma injuries. When organs or tissues are subjected to prolonged hypoxia, danger signals-known as damage-associated molecular patterns (DAMPs)-are released into the intercellular environment. The endothelium is both the target and a major provider of damage-associated molecular patterns, which are directly involved in immuno-inflammatory dysregulation and the associated tissue suffering. Although damage-associated molecular patterns release begins very early after trauma, this release and its consequences continue beyond the initial treatment. Here we review a few examples of damage-associated molecular patterns to illustrate their pathophysiological roles, with emphasis on emerging therapeutic interventions in the context of severe trauma. Therapeutic intervention administered at precise points during damage-associated molecular patterns release may have beneficial effects by calming the inflammatory storm triggered by traumatic hemorrhagic shock.

Plasma proteomics reveals early, broad release of chemokine, cytokine, TNF, and interferon mediators following trauma with delayed increases in a subset of chemokines and cytokines in patients that remain critically ill

Severe injury is known to cause a systemic cytokine storm that is associated with adverse outcomes. However, a comprehensive assessment of the time-dependent changes in circulating levels of a broad spectrum of protein immune mediators and soluble immune mediator receptors in severely injured trauma patients remains uncharacterized. To address this knowledge gap, we defined the temporal and outcome-based patterns of 184 known immune mediators and soluble cytokine receptors in the circulation of severely injured patients. Proteomics (aptamer-based assay, SomaLogic, Inc) was performed on plasma samples drawn at 0, 24, and 72 hours (h) from time of admission from 150 trauma patients, a representative subset from the Prehospital Plasma during Air Medical Transport in Trauma Patients at Risk for Hemorrhagic Shock (PAMPer) trial. Patients were categorized into outcome groups including Early Non-Survivors (died within 72 h; ENS; n=38), Non-Resolvers (died after 72 h or required ≥7 days of intensive care; NR; n=78), and Resolvers (survivors that required < 7 days of intensive care; R; n=34), with low Injury Severity Score (ISS) patients from the Tranexamic Acid During Prehospital Transport in Patients at Risk for Hemorrhage After Injury (STAAMP) trial as controls. The major findings include an extensive release of immune mediators and cytokine receptors at time 0h that is more pronounced in ENS and NR patients. There was a selective subset of mediators elevated at 24 and 72 h to a greater degree in NR patients, including multiple cytokines and chemokines not previously described in trauma patients. These findings were validated in a quantitative fashion using mesoscale discovery immunoassays (MSD) from an external validation cohort (VC) of samples from 58 trauma patients matched for R and NR status. This comprehensive longitudinal description of immune mediator patterns associated with trauma outcomes provides a new level of characterization of the immune response that follows severe injury.

Harnessing Biomaterials for Immunomodulatory-Driven Tissue Engineering

Abstract

The immune system plays a crucial role during tissue repair and wound healing processes. Biomaterials have been leveraged to assist in this in situ tissue regeneration process to dampen the foreign body response by evading or suppressing the immune system. An emerging paradigm within regenerative medicine is to use biomaterials to influence the immune system and create a pro-reparative microenvironment to instigate endogenously driven tissue repair. In this review, we discuss recent studies that focus on immunomodulation of innate and adaptive immune cells for tissue engineering applications through four biomaterial-based mechanisms of action: biophysical cues, chemical modifications, drug delivery, and sequestration. These materials enable augmented regeneration in various contexts, including vascularization, bone repair, wound healing, and autoimmune regulation. While further understanding of immune-material interactions is needed to design the next generation of immunomodulatory biomaterials, these materials have already demonstrated great promise for regenerative medicine.

Lay Summary

The immune system plays an important role in tissue repair. Many biomaterial strategies have been used to promote tissue repair, and recent work in this area has looked into the possibility of doing repair by tuning. Thus, we examined the literature for recent works showcasing the efficacy of these approaches in animal models of injuries. In these studies, we found that biomaterials successfully tuned the immune response and improved the repair of various tissues. This highlights the promise of immune-modulating material strategies to improve tissue repair.

Immune dysfunction following severe trauma: A systems failure from the central nervous system to mitochondria

When a traumatic injury exceeds the body's internal tolerances, the innate immune and inflammatory systems are rapidly activated, and if not contained early, increase morbidity and mortality. Early deaths after hospital admission are mostly from central nervous system (CNS) trauma, hemorrhage and circulatory collapse (30%), and later deaths from hyperinflammation, immunosuppression, infection, sepsis, acute respiratory distress, and multiple organ failure (20%). The molecular drivers of secondary injury include damage associated molecular patterns (DAMPs), pathogen associated molecular patterns (PAMPs) and other immune-modifying agents that activate the hypothalamic-pituitary-adrenal (HPA) axis and sympathetic stress response. Despite a number of drugs targeting specific anti-inflammatory and immune pathways showing promise in animal models, the majority have failed to translate. Reasons for failure include difficulty to replicate the heterogeneity of humans, poorly designed trials, inappropriate use of specific pathogen-free (SPF) animals, ignoring sex-specific differences, and the flawed practice of single-nodal targeting. Systems interconnectedness is a major overlooked factor. We argue that if the CNS is protected early after major trauma and control of cardiovascular function is maintained, the endothelial-glycocalyx will be protected, sufficient oxygen will be delivered, mitochondrial energetics will be maintained, inflammation will be resolved and immune dysfunction will be minimized. The current challenge is to develop new systems-based drugs that target the CNS coupling of whole-body function.

Blast Waves Cause Immune System Dysfunction and Transient Bone Marrow Failure in a Mouse Model

Explosive devices, either conventional or improvised, are common sources of injuries during combat, civil unrest, and terror attacks, resulting in trauma from exposure to blast. A blast wave (BW), a near-instantaneous rise in pressure followed by a negative pressure, propagates through the body in milliseconds and can affect physiology for days/months after exposure. Epidemiological data show that blast-related casualties result in significantly higher susceptibility to wound infections, suggesting long-lasting immune modulatory effects from blast exposure. The mechanisms involved in BW-induced immune changes are poorly understood. We evaluated the effects of BW on the immune system using an established murine model. Animals were exposed to BWs (using an Advanced Blast Simulator), followed by longitudinally sampling for 14 days. Blood, bone marrow, and spleen were analyzed for changes in the 1) complete blood count (CBC), and 2) composition of bone marrow cells (BMC) and splenocytes, and 3) concentrations of systemic cytokines/chemokines. Our data demonstrate that BW results in transient bone marrow failure and long-term changes in the frequency and profile of progenitor cell populations. Viability progressively decreased in hematopoietic stem cells and pluripotent progenitor cells. Significant decrease of CD4⁺ T cells in the spleen indicates reduced functionality of adaptive immune system. Dynamic changes in the concentrations of several cytokines and chemokines such as IL-1α and IL-17 occurred potentially contributing to dysregulation of immune response after trauma. This work lays the foundation for identifying the potential mechanisms behind BW’s immunosuppressive effects to inform the recognition of this compromised status is crucial for the development of therapeutic interventions for infections to reduce recovery time of wounded patients injured by explosive devices.

Internal Fixation Construct and Defect Size Affect Healing of a Translational Porcine Diaphyseal Tibial Segmental Bone Defect

BACKGROUND AND OBJECTIVE

Porcine translational models have become the gold-standard translational tool to study the effects of major injury and hemorrhagic shock because of their similarity to the human immunologic response to trauma. Segmental bone defects (SBDs) typically occur in warfighters with associated severe limb trauma. The purpose of this study was to develop a translational porcine diaphyseal SBD model in Yucatan minipigs (YMPs), which could be used in bone healing investigations that simulate injury-relevant conditions. We were specifically working toward developing a critical sized defect (CSD).

METHODS

We used an adaptive experimental design in which both 25.0 mm and 40.0 mm SBDs were created in the tibial mid-diaphysis in skeletally mature YMPs. Initially, eight YMPs were subjected to a 25.0 mm SBD and treated with intramedullary nailing (intramedullary nail [IMN] 25mm). Due to unanticipated wound problems, we subsequently treated four specimens with identical 25.0 mm defect with dual plating (open reduction with internal fixation [ORIF] 25mm). Finally, a third group of four YMPs with 40.0 mm defects were treated with dual plating (ORIF 40mm). Monthly radiographs were made until sacrifice. Modified Radiographic Union Score for Tibia fractures (mRUST) measurements were made by three trauma-trained orthopedic surgeons. CT scans of the tibias were used to verify the union results.

RESULTS

At 4 months post-surgery, mean mRUST scores were 11.7 (SD ± 1.8) in the ORIF 25mm YMPs vs. 8.5 (SD  ± 1.4) in the IMN 25mm YMPs (P < .0001). All four ORIF 25mm YMPs were clinically healed. In contrast, none of the IMN 25mm YMPs were clinically healed and seven of eight IMN 25mm YMPs developed delayed wound breakdown. All four of the ORIF 40mm YMPs had flail nonunions with complete hardware failure by 3 months after surgery and were sacrificed early. CT scanning confirmed that none of the IMN 25mm YMPs, none of the ORIF 40mm YMPs, and two of four ORIF 25mm YMPs were healed. A third ORIF 25mm specimen was nearly healed on CT scanning. Inter-rater and intra-rater reliability interclass coefficients using the mRUST scale were 0.81 and 0.80, respectively.

CONCLUSIONS

YMPs that had a 40 mm segment of bone removed from their tibia and were treated with dual plating did not heal and could be used to investigate interventions that accelerate bone healing. In contrast, a 25 mm SBD treated with dual plating demonstrated delayed but successful healing, indicating it can potentially be used to investigate bone healing adjuncts or conversely how concomitant injuries may impair bone healing. Pigs treated with IMN failed to heal and developed consistent delayed wound breakdown presumably secondary to chronic limb instability. The porcine YMP SBD model has the potential to be an effective translational tool to investigate bone healing under physiologically relevant injury conditions.

IL-7 Immunotherapy in a Nonimmunocompromised Patient With Intractable Fungal Wound Sepsis

A nonimmunocompromised patient developed life-threatening soft tissue infection with Trichosporon asahii, Fusarium, and Saksenaea that progressed despite maximum antifungal therapies and aggressive debridement. Interleukin-7 immunotherapy resulted in clinical improvement, fungal clearance, reversal of lymphopenia, and improved T-cell function. Immunoadjuvant therapies to boost host immunity may be efficacious in life-threatening fungal infections.

Alarming Cargo: The Role of Exosomes in Trauma-Induced Inflammation

Severe polytraumatic injury initiates a robust immune response. Broad immune dysfunction in patients with such injuries has been well-documented; however, early biomarkers of immune dysfunction post-injury, which are critical for comprehensive intervention and can predict the clinical course of patients, have not been reported. Current circulating markers such as IL-6 and IL-10 are broad, non-specific, and lag behind the clinical course of patients. General blockade of the inflammatory response is detrimental to patients, as a certain degree of regulated inflammation is critical and necessary following trauma. Exosomes, small membrane-bound extracellular vesicles, found in a variety of biofluids, carry within them a complex functional cargo, comprised of coding and non-coding RNAs, proteins, and metabolites. Composition of circulating exosomal cargo is modulated by changes in the intra- and extracellular microenvironment, thereby serving as a homeostasis sensor. With its extensively documented involvement in immune regulation in multiple pathologies, study of exosomal cargo in polytrauma patients can provide critical insights on trauma-specific, temporal immune dysregulation, with tremendous potential to serve as unique biomarkers and therapeutic targets for timely and precise intervention.

Myeloid-derived suppressor cells (MDSC): When good intentions go awry

MDSC are a heterogeneous population of immature myeloid cells that are released by biological stress such as tissue damage and inflammation. Conventionally, MDSC are known for their detrimental role in chronic inflammation and neoplastic conditions. However, their intrinsic functions in immunoregulation, wound healing, and angiogenesis are intended to protect from over-reactive immune responses, maintenance of immunotolerance, tissue repair, and homeostasis. Paradoxically, under certain conditions, MDSC can impair protective immune responses and exacerbate the disease. The transition from protective to harmful MDSC is most likely driven by environmental and epigenetic mechanisms induced by prolonged exposure to unresolved inflammatory triggers. Here, we review several examples of the dual impact of MDSC in conditions such as maternal-fetal tolerance, self-antigens immunotolerance, obesity-associated cancer, sepsis and trauma. Moreover, we also highlighted the evidence indicating that MDSC have a role in COVID-19 pathophysiology. Finally, we have summarized the evidence indicating epigenetic mechanisms associated with MDSC function.

Club Cell Protein 16 Attenuates CD16brightCD62dim Immunosuppressive Neutrophils in Damaged Tissue upon Posttraumatic Sepsis-Induced Lung Injury

Background

Recently, identification of immunosuppressive polymorphonuclear leukocytes (PMNL) that were traditionally described as proinflammatory cells emerged in the field of posttraumatic immunity. To understand their local and remote distribution after trauma, PMNL-subsets and the impact of immunomodulatory Club Cell protein (CC)16 that correlates with pulmonary complications were assessed.

Methods

C57BL/6N mice were divided into three groups, receiving isolated blunt chest trauma (TxT), undergoing TxT followed by cecal ligation and puncture (CLP, TxT + CLP) after 24 h, or sham undergoing analgosedation (n = 18/group). Further, each group was subdivided into three groups receiving either no treatment (ctrl) or intratracheal neutralization of CC16 by application of anti-CC16-antibody or application of an unspecific IgG control antibody (n = 6/group). Treatment was set at the time point after TxT. Analyses followed 6 h post-CLP. PMNL were characterized via expression of CD11b, CD16, CD45, CD62L, and Ly6G by flow cytometry in bone marrow (BM), blood, spleen, lung, liver, and bronchoalveolar and peritoneal lavage fluid (BALF and PL). Apoptosis was assessed by activated (cleaved) caspase-3. Results from untreated ctrl and IgG-treated mice were statistically comparable between all corresponding sham, TxT, and TxT + CLP groups.

Results

Immature (CD16^dimCD62L^bright) PMNL increased significantly in BM, circulation, and spleen after TxT vs. sham and were significantly attenuated in the lungs, BALF, PL, and liver. Classical-shaped (CD16^brightCD62L^bright) PMNL increased after TxT vs. sham in peripheral tissue and were significantly attenuated in circulation, proposing a trauma-induced migration of mature or peripheral differentiation of circulating immature PMNL. Immunosuppressive (CD16^brightCD62L^dim) PMNL decreased significantly in the lungs and spleen, while they systemically increased after TxT vs. sham. CLP in the TxT + CLP group reduced immunosuppressive PMNL in PL and increased their circulatory rate vs. isolated TxT, showing local reduction in affected tissue and their increase in nonaffected tissue. CC16 neutralization enhanced the fraction of immunosuppressive PMNL following TxT vs. sham and decreased caspase-3 in the lungs post-CLP in the TxT + CLP group, while apoptotic cells in the liver diminished post-TxT. Posttraumatic CC16 neutralization promotes the subset of immunosuppressive PMNL and antagonizes their posttraumatic distribution.

Conclusion

Since CC16 affects both the distribution of PMNL subsets and apoptosis in tissues after trauma, it may constitute as a novel target to beneficially shape the posttraumatic tissue microenvironment and homeostasis to improving outcomes.

Platelet-rich plasma accelerates skin wound healing by promoting re-epithelialization

BACKGROUND

Autologous platelet-rich plasma (PRP) has been suggested to be effective for wound healing. However, evidence for its use in patients with acute and chronic wounds remains insufficient. The aims of this study were to comprehensively examine the effectiveness, synergy and possible mechanism of PRP-mediated improvement of acute skin wound repair.

METHODS

Full-thickness wounds were made on the back of C57/BL6 mice. PRP or saline solution as a control was administered to the wound area. Wound healing rate, local inflammation, angiogenesis, re-epithelialization and collagen deposition were measured at days 3, 5, 7 and 14 after skin injury. The biological character of epidermal stem cells (ESCs), which reflect the potential for re-epithelialization, was further evaluated in vitro and in vivo.

RESULTS

PRP strongly improved skin wound healing, which was associated with regulation of local inflammation, enhancement of angiogenesis and re-epithelialization. PRP treatment significantly reduced the production of inflammatory cytokines interleukin-17A and interleukin-1β. An increase in the local vessel intensity and enhancement of re-epithelialization were also observed in animals with PRP administration and were associated with enhanced secretion of growth factors such as vascular endothelial growth factor and insulin-like growth factor-1. Moreover, PRP treatment ameliorated the survival and activated the migration and proliferation of primary cultured ESCs, and these effects were accompanied by the differentiation of ESCs into adult cells following the changes of CD49f and keratin 10 and keratin 14.

CONCLUSION

PRP improved skin wound healing by modulating inflammation and increasing angiogenesis and re-epithelialization. However, the underlying regulatory mechanism needs to be investigated in the future. Our data provide a preliminary theoretical foundation for the clinical administration of PRP in wound healing and skin regeneration.

Better therapy for combat injury

In modern warfare, therapy for combat injury is a critical issue to improve personnel survival and battle effectiveness. Be limited to the severe circumstance in the distant battlefield, quick and effective treatment cannot be supplied that leads infections, sepsis, multiple organ dysfunction syndrome (MODS) and high mortality. To get a better therapy for combat injury, we summarized several reports that associated with the mechanisms of sepsis and MODS, those published on MMR recently. Chaudry and colleagues reported gender difference in the outcomes of trauma, shock and sepsis. The advantageous outcome in female is due to their hormone milieu. Their accumulating reports indicated estrogen as a beneficial factor for multiple system and organs, including the central nervous system, the cardiopulmonary system, the liver, the kidneys, the immune system, and leads to better survival from sepsis. Thompson et al. reviewed the underlying mechanisms in trauma induced sepsis, which can be concluded as an imbalance of immune response triggered by damage-associated molecular patterns (DAMPs) and other immune modifying agents. They also emphasize immunomodulation as a better therapeutic strategy that might be a potential benefit in regulating the host immune response. Fan et al. have revealed a crucial mechanism underlying lung epithelial and macrophage crosstalk, which involves IL-25 as a mediator. After the injury, lung epithelial secreted IL-25 promotes TNF-α production in macrophage leading to acute lung injury (ALI). In addition to a mountain of cytokines, mitochondrial dysfunction in immune cell is another critical risk factor for immune dysfunction during sepsis. Both morphology and function alterations in mitochondria are closely associated with inadequate ATP production, insufficient metabolism process and overloaded  ROS production, which lead harm to immune cells and other tissues by triggering oxidative stress. All the above reports discussed mechanisms of sepsis induction after trauma and provided evidence to improve better therapy strategies targeting diverse risk factors.

Early Local Inhibition of Club Cell Protein 16 Following Chest Trauma Reduces Late Sepsis-Induced Acute Lung Injury

Blunt thoracic trauma (TxT) deteriorates clinical post-injury outcomes. Ongoing inflammatory changes promote the development of post-traumatic complications, frequently causing Acute Lung Injury (ALI). Club Cell Protein (CC)16, a pulmonary anti-inflammatory protein, correlates with lung damage following TxT. Whether CC16-neutralization influences the inflammatory course during ALI is elusive. Ninety-six male CL57BL/6N mice underwent a double hit model of TxT and cecal ligation puncture (CLP, 24 h post-TxT). Shams underwent surgical procedures. CC16 was neutralized by the intratracheal application of an anti-CC16-antibody, either after TxT (early) or following CLP (late). Euthanasia was performed at 6 or 24 h post-CLP. Systemic and pulmonary levels of IL-6, IL-1β, and CXCL5 were determined, the neutrophils were quantified in the bronchoalveolar lavage fluid, and histomorphological lung damage was assessed. ALI induced a significant systemic IL-6 increase among all groups, while the local inflammatory response was most prominent after 24 h in the double-hit groups as compared to the shams. Significantly increased neutrophilic infiltration upon double hit was paralleled with the enhanced lung damage in all groups as compared to the sham, after 6 and 24 h. Neutralization of CC16 did not change the systemic inflammation. However, early CC16-neutralization increased the neutrophilic infiltration and lung injury at 6 h post-CLP, while 24 h later, the lung injury was reduced. Late CC16-neutralization increased neutrophilic infiltration, 24 h post-CLP, and was concurrent with an enhanced lung injury. The data confirmed the anti-inflammatory potential of endogenous CC16 in the murine double-hit model of ALI.