Decreased leukotriene release from neutrophils after severe trauma: role of immature cells

Longitudinal assessment of the inflammatory response: The next step in personalized medicine after severe trauma

Infections in trauma patients are an increasing and substantial cause of morbidity, contributing to a mortality rate of 5-8% after trauma. With increased early survival rates, up to 30-50% of multitrauma patients develop an infectious complication. Trauma leads to a complex inflammatory cascade, in which neutrophils play a key role. Understanding the functions and characteristics of these cells is important for the understanding of their involvement in the development of infectious complications. Recently, analysis of neutrophil phenotype and function as complex biomarkers, has become accessible for point-of-care decision making after trauma. There is an intriguing relation between the neutrophil functional phenotype on admission, and the clinical course (e.g., infectious complications) of trauma patients. Potential neutrophil based cellular diagnostics include subsets based on neutrophil receptor expression, responsiveness of neutrophils to formyl-peptides and FcγRI (CD64) expression representing the infectious state of a patient. It is now possible to recognize patients at risk for infectious complications when presented at the trauma bay. These patients display increased numbers of neutrophil subsets, decreased responsiveness to fMLF and/or increased CD64 expression. The next step is to measure these biomarkers over time in trauma patients at risk for infectious complications, to guide decision making regarding timing and extent of surgery and administration of (preventive) antibiotics.

Neutrophil kinetics and function after major trauma: A systematic review

BACKGROUND

Immune dysfunction following major traumatic injury is complex and strongly associated with significant morbidity and mortality through the development of multiple organ dysfunction syndrome (MODS), persistent inflammation, immunosuppression, and catabolism syndrome and sepsis. Neutrophils are thought to be a pivotal mediator in the development of immune dysfunction.

AIM

To provide a review with a systematic approach of the recent literature describing neutrophil kinetics and functional changes after major trauma in humans and discuss hypotheses as to the mechanisms of the observed neutrophil dysfunction in this setting.

METHODS

Medline, Embase and PubMed were searched on January 15, 2021. Papers were screened by two reviewers and those included had their reference list hand searched for additional papers of interest. Inclusion criteria were adults > 18 years old, with an injury severity score > 12 requiring admission to an intensive care unit. Papers that analysed major trauma patients as a subgroup were included.

RESULTS

Of 107 papers screened, 48 were included in the review. Data were heterogeneous and most studies had a moderate to significant risk of bias owing to their observational nature and small sample sizes. Key findings included a persistently elevated neutrophil count, stereotyped alterations in cell-surface markers of activation, and the elaboration of heterogeneous and immunosuppressive populations of cells in the circulation. Some of these changes correlate with clinical outcomes such as MODS and secondary infection. Neutrophil phenotype remains a promising avenue for the development of predictive markers for immune dysfunction.

CONCLUSION

Understanding of neutrophil phenotypes after traumatic injury is expanding. A greater emphasis on incorporating functional and clinically significant markers, greater uniformity in study design and assessment of extravasated neutrophils may facilitate risk stratification in patients affected by major trauma.

Sterile post-traumatic immunosuppression

After major trauma, the human immune system initiates a series of inflammatory events at the injury site that is later followed by suppression of local inflammation favoring the repair and remodeling of the damaged tissues. This local immune response involves complex interactions between resident cells such as macrophages and dendritic cells, soluble mediators such as cytokines and chemokines, and recruited cells such as neutrophils, monocytes and mesenchymal stromal cells. If of sufficient magnitude, these initial immune responses nevertheless have systemic consequences resulting in a state called post-traumatic immunosuppression (PTI). However, controversy exists regarding the exact immunological changes occurring in systemic compartments triggered by these local immune responses. PTI is one of the leading causes of post-surgical mortality and makes patients vulnerable to hospital-acquired infections, multiple organ failure and many other complications. In addition, hemorrhage, blood transfusion, immunesenescence and immunosuppressant drugs aggravate PTI. PTI has been intensively studied, but published results are frequently cloudy. The purpose of this review is to focus on the contributions made by different responsive modalities to immunosuppression following sterile trauma and to try to integrate these into an overall scheme of PTI.

Kinetics of the innate immune response after trauma: implications for the development of late onset sepsis

BACKGROUND

Severe trauma is characterized by a pronounced immunologic response with both proinflammatory and anti-inflammatory characteristics. The clinical course of trauma patients is often complicated by late-onset (>5 days) sepsis. However, the underlying mechanisms remain poorly defined. Here we studied the kinetics of systemic activation of neutrophils and monocytes following injury in trauma patients in the context of development of sepsis.

METHODS

Thirty-six severely injured patients were included and followed up for 10 days in the intensive care unit. Serial blood samples were taken daily and analyzed ex vivo for activation of PMNs (polymorphonuclear leukocytes, i.e., neutrophils) (expression MAC-1 [macrophage-1 antigen], CXCR-1 [CXC-chemokine receptor 1], FcγRII) and expression of human leukocyte antigen DR (HLA-DR) on monocytes. In addition, the functionality of PMNs was measured by activation of the respiratory burst and responsiveness for the innate immune stimulus N-formyl-methionyl-leucyl-phenylalanine (fMLF).

RESULTS

Ten of 36 patients developed septic shock, invariably 8 to 10 days after admission. CXCR-1 and fMLF-induced active FcγRII showed a gradual decrease in expression before clinical signs of septic shock. Patients who developed septic shock demonstrated a statistically significantly decreased fMLF-induced active FcγRII (P = 0.009) at initial presentation. An immediate decreased percentage of HLA-DR-positive monocytes could be contributed to an increased absolute number of HLA-DR-negative monocytes.

CONCLUSIONS

Phenotyping blood PMNs enables identification of the kinetics and magnitude of the initial systemic inflammatory response after injury. The decreased functionality of PMNs and monocytes reaches its minimum before the development of sepsis and could be an important contributing factor. This could support the early identification of patients at risk.

Deoxyribonuclease is a potential counter regulator of aberrant neutrophil extracellular traps formation after major trauma

Introduction. Neutrophil extracellular traps (NET) consist of a DNA scaffold that can be destroyed by Deoxyribonuclease (DNase). Thus DNases are potential prerequisites for natural counter regulation of NETs formation. In the present study, we determined the relationship of NETs and DNase after major trauma. Methods. Thirty-nine major trauma patients, 14 with and 25 without sepsis development were enrolled in this prospective study. Levels of cell-free (cf)-DNA/NETs and DNase were quantified daily from admission until day 9 after admission. Results. Levels of cf-DNA/NETs in patients who developed sepsis were significantly increased after trauma. In the early septic phase, DNase values in septic patients were significantly increased compared to patients without sepsis (P < 0.05). cf-DNA/NETs values correlated to values of DNase in all trauma patients and patients with uneventful recovery (P < 0.01) but not in septic patients. Recombinant DNase efficiently degraded NETs released by stimulated neutrophils in a concentration-dependent manner in vitro. Conclusions. DNase degrades NETs in a concentration-dependent manner and therefore could have a potential regulatory effect on NET formation in neutrophils. This may inhibit the antibacterial effects of NETs or protect the tissue from autodestruction in inadequate NETs release in septic patients.

Immature circulating neutrophils in sepsis have impaired phagocytosis and calcium signaling

Patients with sepsis commonly develop leukocytosis, which is presumed to reflect a host response to infection. Effective phagocytosis by neutrophils is crucial in the clearance of invading microbes. However, efficacy of phagocytosis in sepsis is controversial. We hypothesized that host phagocytic capacity in sepsis can be affected by immature neutrophils that are released into the circulation. Circulating neutrophils were evaluated in 16 patients with severe sepsis and 5 healthy donors. Immature neutrophils were identified by the cell morphology. Phagocytosis was evaluated by micromanipulation technique and simultaneous cytosolic-free Ca2+ imaging. Leukocytosis was present in 12 of 16 patients. Nine of the 12 patients with leukocytosis and 3 of 4 patients with normal white blood cell counts had increased circulating immature neutrophils (mean, 39.3% +/- 20.7%; normal <or=5%). Quantification of the phagocytic activity revealed a significantly reduced phagocytic index of immature neutrophils as compared with mature neutrophils from both sepsis patients and healthy donors (25% +/- 5% vs. 69% +/- 8% and 42% +/- 6%; P < 0.05). As compared with mature neutrophils, the number of internalized zymosan particles within immature neutrophils was also significantly lower. Mature neutrophils from patients and healthy donors displayed a single rapid transient Ca signal during phagocytosis in contrast with weak signals from immature neutrophils. Our preliminary results show that phagocytic capacity of immature neutrophils is lower as compared with mature neutrophils. An increase in immature neutrophils in severe sepsis may undermine the overall phagocytic efficacy of a host despite observed leukocytosis.

Polytrauma--pathophysiology and management principles

BACKGROUND

Multiple injury results in a complex pathophysiological and immunological response. Depending on the individual injury pattern, the time elapsed after injury, and the systemic "danger response", the surgical treatment has to be modified.

OBJECTIVES

This overview provides new insights in the pathophysiology of the early danger response after polytrauma and outlines the main resulting consequences for surgical management.

RESULTS

First, synchronically to the clinical assessment, life-saving procedures need to be performed rapidly, such as control of massive intra-thoracic or abdominal bleeding and decompression of the chest and brain, as standardized by advanced trauma life support guidelines. During the second phase of "day-one-surgery" damage-control interventions such as debridement, decompression and temporary fracture stabilization are needed to avoid an excessive molecular and cellular danger response. Trauma-adjusted surgical techniques are crucial to limit the systemic response known to put remote organs at risk. In the "vulnerable phase" when the patient's defense is rather uncontrolled, only "second look" debridement to minimize a "second hit" is recommended. After stabilization of the patient as indicated by improvement of tissue oxygenation, coagulation, and decreased inflammatory mediators, "reconstructive surgery" can be applied.

CONCLUSION

Individually adjusted surgical "damage control" and "immune control" are important interactive concepts in polytrauma management.

Morphologic and quantitative analyses of leukocytes in patients with multiple system trauma

Multiple system trauma can occur in accidents, natural disasters, and deliberate attacks, and vital areas of the body, such as the head, chest, and abdomen, may be affected. Investigators in the present study sought to examine morphologic and morphometric alterations of leukocyte responses in patients with multiple trauma during the first 4 h after a traumatic event. Venous blood samples were drawn from 51 patients, 30 male and 21 female, aged 16 to 59 y. The number of leukocytes increased significantly in all patients, but no significant differences were noted between the male and female groups. Complete blood counts revealed normal ratios of leukocyte types. It is suggested that in patients who have experienced multiple trauma, aggressive antibiotic therapy should be initiated to prevent posttraumatic infection and to protect against secondary organ failure.

Leukotriene B4 receptor (BLT-1) modulates neutrophil influx into the peritoneum but not the lung and liver during surgically induced bacterial peritonitis in mice

Leukotriene B4 (LTB4) is a rapidly synthesized, early neutrophil chemoattractant that signals via its cell surface receptor, BLT-1, to attract and activate neutrophils during peritonitis. BLT-1-deficient (BLT-1(-/-)) mice were used to determine the effects of LTB4 on neutrophil migration and activation, bacterial levels, and survival after cecal ligation and puncture (CLP). Male BLT-1(-/-) or wild-type (WT) BALB/c mice underwent CLP. Tissues were harvested for determination of levels of bacteria, myeloperoxidase (MPO), LTB4, macrophage inflammatory protein 2 (MIP-2), and neutrophil (polymorphonuclear leukocyte [PMN]) numbers at 4 and 18 h after CLP. PMN activation was determined by an assessment of phagocytosis ability and CD11b expression. Survival was also determined. BLT-1(-/-) mice had decreased numbers of PMNs in the peritoneum at both 4 and 18 h after CLP but increased numbers of PMNs in the blood at 18 h compared with WT mice. Liver and lung MPO levels were significantly higher in BLT-1(-/-) mice at both 4 and 18 h after CLP, with increased bacterial levels in the blood, the liver, and peritoneal fluid at 4 h. Bacterial levels remained higher in peritoneal fluid at 18 h, but blood and liver bacterial levels at 18 h were not different from levels at 4 h. PMN phagocytosis and CD11b levels were decreased in BLT-1(-/-) mice. LTB4 levels were similar between the groups before and after CLP, but MIP-2 levels were decreased both locally and systemically in BLT-1(-/-) mice. Survival was significantly improved in BLT-1(-/-) mice (71%) compared with WT mice (14%) at 48 h post-CLP. Thus, LTB4 modulates neutrophil migration into the mouse peritoneum, but not the lung or liver, after CLP. Despite higher bacterial and PMN levels at remote sites, there was increased survival in BLT-1(-/-) mice compared to WT mice. Decreased PMN activation may result in less remote organ dysfunction and improved survival.

Impaired blood polymorphonuclear leukocyte migration and infection risk in severe trauma

OBJECTIVES

We investigated the association of impaired blood polymorphonuclear leukocyte (PMN) migration with the incidence of bacterial infections in patients with severe trauma.

METHOD

Twenty-six intensive-care patients with different injury severity scores were enrolled in a prospective study. PMN migration was measured daily using 300 microl fresh whole blood in a membrane filter assay. Migration was evaluated in an automated image analyzer that recorded numbers and distribution of the immigrant PMNs within a filter. The relevant parameter was the percentage of PMNs that migrated from the blood samples into the filters upon f-Met-Leu-Phe stimulation.

RESULTS

Nine patients developed posttraumatic infections verified microbiologically. These patients showed a reduced PMN migratory capacity in comparison with the 17 patients without infections. A migrating portion of six per cent or less at least three days in succession preceded infections by one to 19 days and indicated infection in eight true positive versus three false positive cases, and 14 true negative versus one false negative case, i.e. specificity was 82.3% and sensitivity 88.8%, p=0.0008. Trauma severity had no influence on PMN migration.

CONCLUSIONS

Trauma patients with impaired PMN migration are at risk for bacterial infections. Whole-blood migration tests can define the infection risk and thus may be useful predictive markers for infections.