Microfluidic Assay Measures Increased Neutrophil Extracellular Traps Circulating in Blood after Burn Injuries

PicoGreen assay for nucleic acid quantification - Applications, challenges, and solutions

Various analytical methods and reagents have been employed for nucleic acid analysis in cells, biological fluids, and formulations. Standard techniques like gel electrophoresis and qRT-PCR are widely used for qualitative and quantitative nucleic acid analysis. However, these methods can be time-consuming and labor-intensive, with limitations such as inapplicability to small RNA at low concentrations and high costs associated with qRT-PCR reagents and instruments. As an alternative, PicoGreen (PG) has emerged as a valuable method for the quantitative analysis of nucleic acids. PG, a fluorescent dye, enables the quantitation of double-stranded DNA (dsDNA) or double-stranded RNA, including miRNA mimic and siRNA, in solution. It is also applicable to DNA and RNA analysis within cells using techniques like FACS and fluorescence microscopy. Despite its advantages, PG's fluorescence intensity is affected by various experimental conditions, such as pH, salts, and chemical reagents. This review explores the recent applications of PG as a rapid, cost-effective, robust, and accurate assay tool for nucleic acid quantification. We also address the limitations of PG and discuss approaches to overcome these challenges, recognizing the expanding range of its applications.

IL-8 Induces Neutrophil Extracellular Trap Formation in Severe Thermal Injury

Neutrophil extracellular traps (NETs) have a dual role in the innate immune response to thermal injuries. NETs provide an early line of defence against infection. However, excessive NETosis can mediate the pathogenesis of immunothrombosis, disseminated intravascular coagulation (DIC) and multiple organ failure (MOF) in sepsis. Recent studies suggest that high interleukin-8 (IL-8) levels in intensive care unit (ICU) patients significantly contribute to excessive NET generation. This study aimed to determine whether IL-8 also mediates NET generation in patients with severe thermal injuries. IL-8 levels were measured in serum samples from thermally injured patients with ≥15% of the total body surface area (TBSA) and healthy controls (HC). Ex vivo NET generation was also investigated by treating isolated neutrophils with serum from thermal injured patients or normal serum with and without IL-8 and anti-IL-8 antibodies. IL-8 levels were significantly increased compared to HC on days 3 and 5 (p < 0.05) following thermal injury. IL-8 levels were also significantly increased at day 5 in septic versus non-septic patients (p < 0.001). IL-8 levels were also increased in patients who developed sepsis compared to HC at days 3, 5 and 7 (p < 0.001), day 10 (p < 0.05) and days 12 and 14 (p < 0.01). Serum containing either low, medium or high levels of IL-8 was shown to induce ex vivo NETosis in an IL-8-dependent manner. Furthermore, the inhibition of DNase activity in serum increased the NET-inducing activity of IL-8 in vitro by preventing NET degradation. IL-8 is a major contributor to NET formation in severe thermal injury and is increased in patients who develop sepsis. We confirmed that DNase is an important regulator of NET degradation but also a potential confounder within assays that measure serum-induced ex vivo NETosis.

Distinct functional neutrophil phenotypes in sepsis patients correlate with disease severity

Purpose

Sepsis is a clinical syndrome defined as life-threatening organ dysfunction caused by a dysregulated host response to infection. Sepsis is a highly heterogeneous syndrome with distinct phenotypes that impact immune function and response to infection. To develop targeted therapeutics, immunophenotyping is needed to identify distinct functional phenotypes of immune cells. In this study, we utilized our Organ-on-Chip assay to categorize sepsis patients into distinct phenotypes using patient data, neutrophil functional analysis, and proteomics.

Methods

Following informed consent, neutrophils and plasma were isolated from sepsis patients in the Temple University Hospital ICU (n=45) and healthy control donors (n=7). Human lung microvascular endothelial cells (HLMVEC) were cultured in the Organ-on-Chip and treated with buffer or cytomix ((TNF/IL-1β/IFNγ). Neutrophil adhesion and migration across HLMVEC in the Organ-on-Chip were used to categorize functional neutrophil phenotypes. Quantitative label-free global proteomics was performed on neutrophils to identify differentially expressed proteins. Plasma levels of sepsis biomarkers and neutrophil extracellular traps (NETs) were determined by ELISA.

Results

We identified three functional phenotypes in critically ill ICU sepsis patients based on ex vivo neutrophil adhesion and migration patterns. The phenotypes were classified as: Hyperimmune characterized by enhanced neutrophil adhesion and migration, Hypoimmune that was unresponsive to stimulation, and Hybrid with increased adhesion but blunted migration. These functional phenotypes were associated with distinct proteomic signatures and differentiated sepsis patients by important clinical parameters related to disease severity. The Hyperimmune group demonstrated higher oxygen requirements, increased mechanical ventilation, and longer ICU length of stay compared to the Hypoimmune and Hybrid groups. Patients with the Hyperimmune neutrophil phenotype had significantly increased circulating neutrophils and elevated plasma levels NETs.

Conclusion

Neutrophils and NETs play a critical role in vascular barrier dysfunction in sepsis and elevated NETs may be a key biomarker identifying the Hyperimmune group. Our results establish significant associations between specific neutrophil functional phenotypes and disease severity and identify important functional parameters in sepsis pathophysiology that may provide a new approach to classify sepsis patients for specific therapeutic interventions.

Quantifying neutrophil extracellular trap release in a combined infection-inflammation NET-array device

Excessive release of neutrophil extracellular traps (NETs) has been reported in various human pathologies, including COVID-19 patients. Elevated NET levels serve as a biomarker, indicating increased coagulopathy and immunothrombosis risks in these patients. Traditional immunoassays employed to quantify NET release focus on bulk measurements of released chromatin in simplified microenvironments. In this study, we fabricated a novel NET-array device to quantify NET release from primary human neutrophils with single-cell resolution in the presence of the motile bacteria Pseudomonas aeruginosa PAO1 and inflammatory mediators. The device was engineered to have wide chambers and constricted loops to measure NET release in variably confined spaces. Our open NET-array device enabled immunofluorescent labeling of citrullinated histone H3, a NET release marker. We took time-lapse images of primary healthy human neutrophils releasing NETs in clinically relevant infection and inflammation-rich microenvironments. We then developed a computer-vision-based image processing method to automate the quantification of individual NETs. We showed a significant increase in NET release to Pseudomonas aeruginosa PAO1 when challenged with inflammatory mediators tumor necrosis factor-α [20 ng mL-1] and interleukin-6 [50 ng mL-1], but not leukotriene B4 [20 nM], compared to the infection alone. We also quantified the temporal dynamics of NET release and differences in the relative areas of NETs, showing a high percentage of variable size NET release with combined PAO1 - inflammatory mediator treatment, in the device chambers. Importantly, we demonstrated reduced NET release in the confined loops of our combined infection-inflammation microsystem. Ultimately, our NET-array device stands as a valuable tool, facilitating experiments that enhance our comprehension of the spatiotemporal dynamics of NET release in response to infection within a defined microenvironment. In the future, our system can be used for high throughput and cost-effective screening of novel immunotherapies on human neutrophils in view of the importance of fine-tuning NET release in controlling pathological neutrophil-driven inflammation.

Murine scald models characterize the role of neutrophils and neutrophil extracellular traps in severe burns

Introduction

Severe burns cause unique pathophysiological alterations especially on the immune system. A murine scald model was optimized as a basis for the understanding of immunological reactions in response to heat induced injury. The understanding of the roles of neutrophil extracellular traps (NETs) and DNases will support the development of new surgical or pharmacological strategies for the therapy of severe burns.

Methods

We studied C57BL/6 mice (n=30) and employed four scalding protocols with varying exposure times to hot water. An additional scald group with a shorter observational time was generated to reduce mortality and study the very early phase of pathophysiology. At 24h or 72h, blood was drawn and tissue (wound, liver, lung, spleen) was analyzed for the presence of NETs, oxidative stress, apoptosis, bacterial translocation, and extracellular matrix re-organization. In addition, we analyzed the transcriptome from lung and liver tissues.

Results

Exposure to hot water for 7s led to significant systemic and local effects and caused considerable late mortality. Therefore, we used an observation time of 24h in this groups. To study later phases of burns (72h) an exposure time of 6s is optimal. Both conditions led to significant disorganization of collagen, increased oxidative stress, NET formation (by immunodetection of H3cit, NE, MPO), apoptosis (cC3) and alterations of the levels of DNase1 and DNase1L3. Transcriptome analysis revealed remarkable alterations in genes involved in acute phase signaling, cell cohesion, extracellular matrix organization, and immune response.

Conclusion

We identified two scald models that allow the analysis of early (24h) or late (72h) severe burn effects, thereby generating reproducible and standardized scald injuries. The study elucidated the important involvement of neutrophil activity and the role of NETs in burns. Extensive transcriptome analysis characterized the acute phase and tissue remodeling pathways involved in the process of healing and may serve as crucial basis for future in-depth studies.

LEUKOCYTE PHENOTYPING IN SEPSIS USING OMICS, FUNCTIONAL ANALYSIS, AND IN SILICO MODELING

ABSTRACT

Sepsis is a major health issue and a leading cause of death in hospitals globally. The treatment of sepsis is largely supportive, and there are no therapeutics available that target the underlying pathophysiology of the disease. The development of therapeutics for the treatment of sepsis is hindered by the heterogeneous nature of the disease. The presence of multiple, distinct immune phenotypes ranging from hyperimmune to immunosuppressed can significantly impact the host response to infection. Recently, omics, biomarkers, cell surface protein expression, and immune cell profiles have been used to classify immune status of sepsis patients. However, there has been limited studies of immune cell function during sepsis and even fewer correlating omics and biomarker alterations to functional consequences. In this review, we will discuss how the heterogeneity of sepsis and associated immune cell phenotypes result from changes in the omic makeup of cells and its correlation with leukocyte dysfunction. We will also discuss how emerging techniques such as in silico modeling and machine learning can help in phenotyping sepsis patients leading to precision medicine.

Cell-Free DNA in the Pathogenesis and Therapy of Non-Infectious Inflammations and Tumors

The basic function of the immune system is the protection of the host against infections, along with the preservation of the individual antigenic identity. The process of self-tolerance covers the discrimination between self and foreign antigens, including proteins, nucleic acids, and larger molecules. Consequently, a broken immunological self-tolerance results in the development of autoimmune or autoinflammatory disorders. Immunocompetent cells express pattern-recognition receptors on their cell membrane and cytoplasm. The majority of endogenous DNA is located intracellularly within nuclei and mitochondria. However, extracellular, cell-free DNA (cfDNA) can also be detected in a variety of diseases, such as autoimmune disorders and malignancies, which has sparked interest in using cfDNA as a possible biomarker. In recent years, the widespread use of liquid biopsies and the increasing demand for screening, as well as monitoring disease activity and therapy response, have enabled the revival of cfDNA research. The majority of studies have mainly focused on the function of cfDNA as a biomarker. However, research regarding the immunological consequences of cfDNA, such as its potential immunomodulatory or therapeutic benefits, is still in its infancy. This article discusses the involvement of various DNA-sensing receptors (e.g., absent in melanoma-2; Toll-like receptor 9; cyclic GMP-AMP synthase/activator of interferon genes) in identifying host cfDNA as a potent danger-associated molecular pattern. Furthermore, we aim to summarize the results of the experimental studies that we recently performed and highlight the immunomodulatory capacity of cfDNA, and thus, the potential for possible therapeutic consideration.

Engineering physical microenvironments to study innate immune cell biophysics

Innate immunity forms the core of the human body's defense system against infection, injury, and foreign objects. It aims to maintain homeostasis by promoting inflammation and then initiating tissue repair, but it can also lead to disease when dysregulated. Although innate immune cells respond to their physical microenvironment and carry out intrinsically mechanical actions such as migration and phagocytosis, we still do not have a complete biophysical description of innate immunity. Here, we review how engineering tools can be used to study innate immune cell biophysics. We first provide an overview of innate immunity from a biophysical perspective, review the biophysical factors that affect the innate immune system, and then explore innate immune cell biophysics in the context of migration, phagocytosis, and phenotype polarization. Throughout the review, we highlight how physical microenvironments can be designed to probe the innate immune system, discuss how biophysical insight gained from these studies can be used to generate a more comprehensive description of innate immunity, and briefly comment on how this insight could be used to develop mechanical immune biomarkers and immunomodulatory therapies.

Microfluidic capture of chromatin fibres measures neutrophil extracellular traps (NETs) released in a drop of human blood

Neutrophils are the largest population of white blood cells in the circulation, and their primary function is to protect the body from microbes. They can release the chromatin in their nucleus, forming characteristic web structures and trap microbes, contributing to antimicrobial defenses. The chromatin webs are known as neutrophil extracellular traps (NETs). Importantly, neutrophils can also release NETs in pathological conditions related to rheumatic diseases, atherosclerosis, cancer, and sepsis. Thus, determining the concentration of NETs in the blood is increasingly important for monitoring patients, evaluating treatment efficacy, and understanding the pathology of various diseases. However, traditional methods for measuring NETs require separating cells and plasma from blood, are prone to sample preparation artifacts, and cannot distinguish between intact and degraded NETs. Here, we design a microfluidic analytical tool that captures NETs mechanically from a drop of blood and measures the amount of intact NETs unbiased by the presence of degraded NETs in the sample.

Microfluidic Systems to Study Neutrophil Forward and Reverse Migration

During infection, neutrophils are the most abundantly recruited innate immune cells at sites of infection, playing critical roles in the elimination of local infection and healing of the injury. Neutrophils are considered to be short-lived effector cells that undergo cell death at infection sites and in damaged tissues. However, recent in vitro and in vivo evidence suggests that neutrophil behavior is more complex and that they can migrate away from the inflammatory site back into the vasculature following the resolution of inflammation. Microfluidic devices have contributed to an improved understanding of the interaction and behavior of neutrophils ex vivo in 2D and 3D microenvironments. The role of reverse migration and its contribution to the resolution of inflammation remains unclear. In this review, we will provide a summary of the current applications of microfluidic devices to investigate neutrophil behavior and interactions with other immune cells with a focus on forward and reverse migration in neutrophils.

Human Neutrophils Respond to Complement Activation and Inhibition in Microfluidic Devices

Complement activation is key to anti-microbial defenses by directly acting on microbes and indirectly by triggering cellular immune responses. Complement activation may also contribute to the pathogenesis of numerous inflammatory and immunological diseases. Consequently, intense research focuses on developing therapeutics that block pathology-causing complement activation while preserving anti-microbial complement activities. However, the pace of research is slowed down significantly by the limitations of current tools for evaluating complement-targeting therapeutics. Moreover, the effects of potential therapeutic agents on innate immune cells, like neutrophils, are not fully understood. Here, we employ microfluidic assays and measure chemotaxis, phagocytosis, and swarming changes in human neutrophils ex vivo in response to various complement-targeting agents. We show that whereas complement factor 5 (C5) cleavage inhibitor eculizumab blocks all neutrophil anti-microbial functions, newer compounds like the C5 cleavage inhibitor RA101295 and C5a receptor antagonist avacopan inhibit chemotaxis and swarming while preserving neutrophil phagocytosis. These results highlight the utility of microfluidic neutrophil assays in evaluating potential complement-targeting therapeutics.

Modeled vascular microenvironments: immune-endothelial cell interactions in vitro

The advancement of in vitro techniques enables a better understanding of biological processes and improves drug screening platforms. In vitro studies allow for enhanced observation of cell behavior, control over the mimicked microenvironment, and the ability to use human cells. In particular, advances in vascular microenvironment recapitulation are of interest given vasculature influence in cardiovascular vascular diseases and cancer. These investigate alterations in endothelial cell behavior and immune cell interactions with endothelial cells. Specific immune cells such as monocytes, macrophages, neutrophils, and T cells influence endothelial cell behavior by promoting or inhibiting vasculogenesis through cell-cell interaction or soluble signaling. Results from these studies showcase cell behavior in vascular diseases and in the context of tumor metastasis. In this review, we discuss examples of in vitro studies modeling immune cell-endothelial cell interactions to present methods and recent findings in the field. Schematic showcasing common methods of in vitro experimentation of endothelial-immune cell interactions, including interactions with flow, static culture, or in-direct contact.

A Novel Microfluidic Device for the Neutrophil Functional Phenotype Analysis: Effects of Glucose and Its Derivatives AGEs

Neutrophil dysfunction is closely related to the pathophysiology of patients with diabetes mellitus, but existing immunoassays are difficult to implement in clinical applications, and neutrophil’s chemotaxis as a functional biomarker for diabetes mellitus prognostic remains largely unexplored. Herein, a novel microfluidic device consisted of four independent test units with four cell docking structures was developed to study the neutrophil chemotaxis, which allowed multiple cell migration observations under a single field of view (FOV) and guaranteed more reliable results. In vitro studies, the chemotaxis of healthy neutrophils to N-Formyl-Met-Leu-Phe (fMLP) gradient (0, 10, 100, and 1000 nM) was concentration-dependent. The distinct promotion or suppression in the chemotaxis of metformin or pravastatin pretreated cells were observed after exposure to 100 nM fMLP gradient, indicating the feasibility and efficiency of this novel microfluidic device for clinically relevant evaluation of neutrophil functional phenotype. Further, the chemotaxis of neutrophils pretreated with 25, 50, or 70 mM of glucose was quantitatively lower than that of the control groups (i.e., 5 mM normal serum level). Neutrophils exposed to highly concentrated advanced glycation end products (AGEs) (0.2, 0.5, or 1.0 μM; 0.13 μM normal serum AGEs level), a product of prolonged hyperglycemia, showed that the higher the AGEs concentration was, the weaker the migration speed became. Specifically, neutrophils exposed to high concentrations of glucose or AGEs also showed a stronger drifting along with the flow, further demonstrating the change of neutrophil chemotaxis. Interestingly, adding the N-benzyl-4-chloro-N-cyclohexylbenzamide (FPS-ZM1) (i.e., high-affinity RAGE inhibitor) into the migration medium with AGEs could hinder the binding between AGEs and AGE receptor (RAGE) located on the neutrophil, thereby keeping the normal chemotaxis of neutrophils than the ones incubated with AGEs alone. These results revealed the negative effects of high concentrations of glucose and AGEs on the neutrophil chemotaxis, suggesting that patients with diabetes should manage serum AGEs and also pay attention to blood glucose indexes. Overall, this novel microfluidic device could significantly characterize the chemotaxis of neutrophils and have the potential to be further improved into a tool for risk stratification of diabetes mellitus.

Neutrophils initiate and exacerbate Stevens-Johnson syndrome and toxic epidermal necrolysis

Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN) are life-threatening mucocutaneous adverse drug reactions characterized by massive epidermal detachment. Cytotoxic T cells and associated effector molecules are known to drive SJS/TEN pathophysiology, but the contribution of innate immune responses is not well understood. We describe a mechanism by which neutrophils triggered inflammation during early phases of SJS/TEN. Skin-infiltrating CD8⁺ T cells produced lipocalin-2 in a drug-specific manner, which triggered the formation of neutrophil extracellular traps (NETs) in early lesional skin. Neutrophils undergoing NETosis released LL-37, an antimicrobial peptide, which induced formyl peptide receptor 1 (FPR1) expression by keratinocytes. FPR1 expression caused keratinocytes to be vulnerable to necroptosis that caused further release of LL-37 by necroptotic keratinocytes and induced FPR1 expression on surrounding keratinocytes, which likely amplified the necroptotic response. The NETs-necroptosis axis was not observed in less severe cutaneous adverse drug reactions, autoimmune diseases, or neutrophil-associated disorders, suggesting that this was a process specific to SJS/TEN. Initiation and progression of SJS/TEN keratinocyte necroptosis appear to involve a cascade of events mediated by innate and adaptive immune responses, and understanding these responses may contribute to the identification of diagnostic markers or therapeutic targets for these adverse drug reactions.

Microphysiological Systems for Studying Cellular Crosstalk During the Neutrophil Response to Infection

Neutrophils are the primary responders to infection, rapidly migrating to sites of inflammation and clearing pathogens through a variety of antimicrobial functions. This response is controlled by a complex network of signals produced by vascular cells, tissue resident cells, other immune cells, and the pathogen itself. Despite significant efforts to understand how these signals are integrated into the neutrophil response, we still do not have a complete picture of the mechanisms regulating this process. This is in part due to the inherent disadvantages of the most-used experimental systems: in vitro systems lack the complexity of the tissue microenvironment and animal models do not accurately capture the human immune response. Advanced microfluidic devices incorporating relevant tissue architectures, cell-cell interactions, and live pathogen sources have been developed to overcome these challenges. In this review, we will discuss the in vitro models currently being used to study the neutrophil response to infection, specifically in the context of cell-cell interactions, and provide an overview of their findings. We will also provide recommendations for the future direction of the field and what important aspects of the infectious microenvironment are missing from the current models.

Neutrophil dysfunction in cystic fibrosis

BACKGROUND

Excessive neutrophil inflammation is the hallmark of cystic fibrosis (CF) airway disease. Novel technologies for characterizing neutrophil dysfunction may provide insight into the nature of these abnormalities, revealing a greater mechanistic understanding and new avenues for CF therapies that target these mechanisms.

METHODS

Blood was collected from individuals with CF in the outpatient clinic, CF individuals hospitalized for a pulmonary exacerbation, and non-CF controls. Using microfluidic assays and advanced imaging technologies, we characterized 1) spontaneous neutrophil migration using microfluidic motility mazes, 2) neutrophil migration to and phagocytosis of Staphylococcal aureus particles in a microfluidic arena, 3) neutrophil swarming on Candida albicans clusters, and 4) Pseudomonas aeruginosa-induced neutrophil transepithelial migration using micro-optical coherence technology (µOCT).

RESULTS

Participants included 44 individuals: 16 Outpatient CF, 13 Hospitalized CF, and 15 Non-CF individuals. While no differences were seen with spontaneous migration, CF neutrophils migrated towards S. aureus particles more quickly than non-CF neutrophils (p < 0.05). CF neutrophils, especially Hospitalized CF neutrophils, generated significantly larger aggregates around S. aureus particles over time. Hospitalized CF neutrophils were more likely to have dysfunctional swarming (p < 0.01) and less efficient clearing of C. albicans (p < 0.0001). When comparing trans-epithelial migration towards Pseudomonas aeruginosa epithelial infection, Outpatient CF neutrophils displayed an increase in the magnitude of transmigration and adherence to the epithelium (p < 0.05).

CONCLUSIONS

Advanced technologies for characterizing CF neutrophil function reveal significantly altered migratory responses, cell-to-cell clustering, and microbe containment. Future investigations will probe mechanistic basis for abnormal responses in CF to identify potential avenues for novel anti-inflammatory therapeutics.

Recombinant human ADAMTS13 treatment and anti-NET strategies enhance skin allograft survival in mice

Enhancing skin allograft longevity lessens the need for new allografts before optimal intervention is available. Reduced activity of ADAMTS13 (an enzyme that cleaves the pro-thrombotic and proinflammatory von Willebrand factor) and presence of neutrophil extracellular traps (NETs) have been implicated in liver and lung allograft failures. The effect of ADAMTS13 treatment and the impact of NETs on skin allografts, however, remain unexplored. Here, we adopted a murine model of complete mismatch full-thickness skin transplant by grafting dorsal skin from BALB/c mice to C57BL/6J background mice. Recombinant human ADAMTS13 (rhADAMTS13) treatment of graft recipients increased allograft survival. Western blot and immunofluorescence microscopy revealed the presence of NETs in allografts of vehicle, but surprisingly, not in rhADAMTS13-treated mice, 3 days after surgery. Recapitulating the observations in mice, NETs were also observed in all the examined allografts from burn patients. Intriguingly, knocking out peptidylarginine deiminase 4 (PAD4, a key enzyme for NET formation) or DNase 1 treatment (which cleaves NETs) also prolonged allograft survival. In summary, rhADAMTS13 lessens inflammation in allografts by reducing NET burden, resulting in enhanced allograft survival. RhADAMTS13 and anti-NET treatments could be new therapeutic strategies to promote skin allograft longevity and, hence, the survival of patients with severe burns.

Dysregulation of the actin scavenging system and inhibition of DNase activity following severe thermal injury

Background

Circulating cell‐free DNA (cfDNA) is not found in healthy subjects, but is readily detected after thermal injury and may contribute to the risk of multiple organ failure. The hypothesis was that a postburn reduction in DNase protein/enzyme activity could contribute to the increase in cfDNA following thermal injury.

Methods

Patients with severe burns covering at least 15 per cent of total body surface area were recruited to a prospective cohort study within 24 h of injury. Blood samples were collected from the day of injury for 12 months.

Results

Analysis of blood samples from 64 patients revealed a significant reduction in DNase activity on days 1–28 after injury, compared with healthy controls. DNase protein levels were not affected, suggesting the presence of an enzyme inhibitor. Further analysis revealed that actin (an inhibitor of DNase) was present in serum samples from patients but not those from controls, and concentrations of the actin scavenging proteins gelsolin and vitamin D‐binding protein were significantly reduced after burn injury. In a pilot study of ten military patients with polytrauma, administration of blood products resulted in an increase in DNase activity and gelsolin levels.

Conclusion

The results of this study suggest a novel biological mechanism for the accumulation of cfDNA following thermal injury by which high levels of actin released by damaged tissue cause a reduction in DNase activity. Restoration of the actin scavenging system could therefore restore DNase activity, and reduce the risk of cfDNA‐induced host tissue damage and thrombosis.