L-selectin shows time and gender dependency in association with MODS

Altered cell surface receptor dynamics and circulatory occurrence of neutrophils in a small animal fracture model

INTRODUCTION

Excessive activation of the immune response after femoral fractures and fracture fixation is potentially associated with the development of systemic and local complications, particularly in multiple trauma patients. A dysregulated function of neutrophils, the most prevailing immune cells in circulation, has been discussed as a central pathophysiological background for these unfavourable post-traumatic courses. Our aim was to investigate alterations in activity and functionality as expressed by the cell surface receptor dynamics of circulatory neutrophils after femoral fracture and intramedullary stabilization.

MATERIAL AND METHODS

After intramedullary stabilization, an isolated femur fracture was induced in 18 Sprague-Dawley rats. Animals were terminated at different time points, i.e. after 3 (n = 5, group 3d), 7 (n = 5, group 7d) and 14 (n = 5, Group 14d) days and grouped accordingly. Additionally, baseline measurements were performed in one control animal per study group (n = 3) after anaesthesia induction and termination, without prior intramedullary nailing and fracture induction. The numbers and cell surface expression of CD11b, CD11a, CD62 L, and CD49d of circulating neutrophils were compared between groups.

RESULTS

Neutrophil numbers were significantly reduced at 3 days compared with baseline measurements (1.2 × 10⁵ vs. 6.3 × 10⁵ cells/mL, p < 0.01). By day 7, neutrophil counts significantly increased back to homeostatic levels (p < 0.05). At day 3, CD11b-expression was significantly reduced, whereas CD11a-expression was increased compared with the baseline measurements (p < 0.05). At day 7, the circulatory neutrophil pool exhibited a unique CD11b^high/CD11a^high-neutrophil subset showing a significantly increased co-expression of CD49d. The expression of CD62 L did not change significantly throughout the experiment compared with baseline measurements.

CONCLUSIONS

This descriptive small animal fracture study is the first to show that an intramedullary stabilized femur fracture is associated with a temporary reduction in circulatory neutrophil count and concurrent changes in circulatory neutrophil function. Moreover, we demonstrated that the restoration to homeostatic neutrophil activation status occurs concomitantly with the appearance of a novel neutrophil subtype (CD11b^high/CD11a^high) in circulation. Our fundamental new findings of the changes in circulatory neutrophil count and functionality after trauma form an excellent basis for future studies to further elucidate the role of neutrophils as activators and regulators of different post-traumatic processes, potentially resulting in local (e.g., fracture healing disturbances) or systemic (e.g., MODS) complications. This might result in the development of specific therapies to reduce adverse outcomes after trauma.

The Importance of Sex Differences on Outcome after Major Trauma: Clinical Outcome in Women Versus Men

Purpose: The purpose of this study was to evaluate epidemiological and clinically relevant sex-related differences in polytraumatized patients at a Level 1 Trauma Center. Methods: 646 adult patients (210 females and 436 males) who were classified as polytraumatized (at the point of admission) and treated at our Level I Trauma Center were reviewed and included in this study. Demographic data as well as mechanism of injury, injury severity, injury pattern, frequency of preclinical intubation, hemodynamic variables on admission, time of mechanical ventilation and of intensive care unit (ICU) treatment, as well as the incidence of acute respiratory distress syndrome (ARDS), multi organ failure (MOF), and mortality were extracted and analyzed. Results: A total of 210 female and 436 male patients formed the basis of this report. Females showed a higher mean age (44.6 vs. 38.3 years; p < 0.0001) than their male counterparts. Women were more likely to be injured as passengers or by suicidal falls whereas men were more likely to suffer trauma as motorcyclists. Following ICU treatment, female patients resided significantly longer at the casualty ward than men (27.1 days vs. 20.4 days, p = 0.013) although there was no significant difference regarding injury severity, hemodynamic variables on admission, and incidence of MOF, ARDS, and mortality. Conclusion: The positive correlation of higher age and longer in-hospital stay in female trauma victims seems to show women at risk for a prolonged in-hospital rehabilitation time. A better understanding of the impact of major trauma in women (but also men) will be an important component of efforts to improve trauma care and long-term outcome.

Regulation of L-selectin expression by trauma-relevant cytokines

The leukocyte adhesion molecule L-selectin is important for the rolling of neutrophil granulocytes (PMN), the first step of the cascade leading to adhesion, diapedesis, and subsequent organ dysfunction. The activation of leukocytes in the posttraumatic course is assumed to be induced by different pro-inflammatory cytokines. In the present study, we investigated the effects of stimulation with pro- and anti-inflammatory cytokines on the L-selectin surface expression on PMN. Twenty patients admitted to our institution for elective operations of the lower extremities were enrolled in a prospective clinical study. For the measurement of L-selectin expression, blood was taken before the operation (0 h), as well as 24 h and 48 h postoperatively. Without and after incubation with different pro- and anti-inflammatory cytokines (TNF-α, IL-1β, IL-6 and IL-10), the surface expression of L-selectin was detected using an anti-L-selectin-specific antibody and flow cytometry. L-selectin surface expression without any stimulation showed a non-significant increase 48 h after the operation (63.6±6.6 ng/ml at 0 h, 95.2±10.5 ng/ml at 48 h). Stimulation with TNF-α resulted in a significant decrease of L-selectin expression at 0 h (25.6±2.7 ng/ml; p<0.05) and 24 h (18.3±2.5 ng/ml; p<0.05), but not at 48 h (39.8±4.2 ng/ml). No significant differences were observed after stimulation with IL-1β, IL-6, and IL-10 in comparison to the non-stimulated group. The study results indicate that the primary pro-inflammatory cytokine TNF-α regulates the L-selectin surface expression on PMN after surgical trauma. Therefore, a regulation of neutrophil activation on this level might be crucial in the development of posttraumatic complications.

Isolated blunt chest injury leads to transient activation of circulating neutrophils

Introduction

The acute respiratory distress syndrome (ARDS) is a severe and frequently seen complication in multi-trauma patients. ARDS is caused by an excessive innate immune response with a clear role for neutrophils. As ARDS is more frequently seen in trauma patients with chest injury, we investigated the influence of chest injury on the systemic neutrophil response and the development of ARDS.

Materials and methods

Thirteen patients with isolated blunt chest injury [abbreviated injury score (AIS) 2–5] were included. To avoid systemic inflammation caused by tissue damage outside the thorax, injuries to other regions than the chest did not exceed an AIS of 2. At 3, 9 and 24 h after injury, the expression of circulating activating molecules on neutrophils and levels of circulating interleukine (IL)-6 were determined. Blood samples from eight healthy volunteers were used as control.

Results

Blunt chest injury resulted in the activation of circulating neutrophils, as characterized by a decreased expression of l-selectin (CD62L), CXCR2 (CD182b) and C5aR (CD88) compared to control (p < 0.05). Expression of l-selectin, CXCR2 and C5aR was partially restored at 24 h after injury. In addition, the mean expression of FcγRIII (CD16) dropped (p < 0.001), indicating the recruitment of young neutrophils into the circulation. IL-6 levels increased to a maximum mean concentration of 86 ± 31 pg/ml at 24 h postinjury. None of the patients developed ARDS.

Conclusion

Blunt chest trauma caused a systemic inflammatory reaction with transient activation of neutrophils and mobilization of young neutrophils into the circulation. Isolated chest injury, however, was not abundant enough to cause ARDS, so a second hit appears crucial.

Effects of changing strategies of fracture fixation on immunologic changes and systemic complications after multiple trauma: damage control orthopedic surgery

In the treatment of polytrauma patients, multiple studies have shown how the timing and the type of the initial surgery of long bone fractures influence the incidence of systemic complications. Database analyses documented that unduly long surgical procedures undertaken early after trauma increase the risk of acute respiratory distress syndrome (ARDS), especially when femoral shaft fractures are stabilized. Animal research and prospective clinical studies also support the fact that the type of stabilization of a femoral shaft fracture may influence the systemic response to trauma. Reamed intramedullary reaming and nailing for a femoral shaft fracture is associated with an increased risk of pulmonary fat embolization from the medullary canal. This can result in pulmonary compromise if certain cofactors are also present. Modified reamers have been developed to reduce this side effect. The mediating effects are immunologic changes, varying according to the magnitude of the surgical procedure. Pro-inflammatory markers (e.g., Interleukins) may be used to assess the inflammatory response to injury as well as the magnitude of surgery and the systemic impact induced by surgery. Serum levels of such markers can be used clinically to tailor the amount of surgery that is performed to the clinical condition of the patient. The potentially negative impact of excessive surgery in high-risk patients can be avoided by using a new grading system for the assessment of the clinical status of the injured patient. Most recently, a large prospective randomized multicenter study has documented that this grading system is effective for identifying these borderline patients, and that in the borderline patient a staged surgical approach, such as temporary femoral stabilization with an external fixator, reduces the incidence of systemic complications. This work has changed the surgical management of multiply injured patients toward an approach that is tailored to the clinical condition of the patient, as indicated by well-defined clinical parameters as well as objective measurements of serum cytokine levels.

Quantification and characterisation of endothelial injury after trauma

The microenvironment theory has become very popular for providing mechanisms which explain the development of often lethal posttraumatic complications such as systemic inflammatory response syndrome (SIRS), adult respiratory distress syndrome (ARDS) and multiple organ dysfunction syndrome (MODS). With the recent advances in molecular biology and the ever-expanding understanding of trauma pathophysiology, immunomonitoring in trauma patients attempts to characterise and quantify novel molecules in order to predict patients at risk. This review article assesses the existing evidence on the biomarkers of endothelial injury and their potential utility as quantification parameters of endothelial dysfunction in trauma patients.

L-selectin: adhesion, signalling and its importance in pathologic posttraumatic endotoxemia and non-septic inflammation

The leucocyte expressed surface-bound L-selectin belongs to the selectin family of adhesion molecules. It exhibits adhesive as well as signalling functions. Mainly, it is of importance in lymphocyte homing and in the extravasation of leucocytes into the surrounding tissue during inflammation. Acting in the initial step of the cell adhesion cascade, L-selectin is responsible for the rolling of leucocytes on endothelial layers. Therefore, L-selectin is thought to be an adequate target for pharmacological interventions. Beneath the discussion of the molecules' general features like molecule structure and its regulation, the review focuses firstly on L-selectin in the context of posttraumatic inflammatory disorders, and secondly on the importance of L-selectin specific signalling events.