Background: Severe traumatic injury has been associated with high susceptibility for the development of secondary complications caused by dysbalanced immune response. As the first line of the cellular immune response, neutrophils and monocytes recruited to the site of tissue damage and/or infection, are divided into three different subsets according to their CD16/CD62L and CD16/CD14 expression, respectively. Their differential functions have not yet been clearly understood. Thus, we evaluated the phenotypic changes of neutrophil and monocyte subsets among their functionality regarding oxidative burst and the phagocytic capacity in severely traumatized patients. Methods: Peripheral blood was withdrawn from severely injured trauma patients (TP; n = 15, ISS ≥ 16) within the first 12 h post-trauma and from healthy volunteers (HV; n = 15) and stimulated with fMLP and PMA. CD16^dimCD62L^bright (immature), CD16^brightCD62L^bright (mature) and CD16^brightCD62L^dim (CD62L^low) neutrophil subsets and CD14^brightCD16⁻ (classical), CD14^brightCD16⁺ (intermediate) and CD14^dimCD16⁺ (non-classical) monocyte subsets of HV and TP were either directly analyzed by flow cytometry or the examined subsets of HV were sorted first by fluorescence-activated cell sorting and subsequently analyzed. Subset-specific generation of reactive oxygen species (ROS) and of E. coli bioparticle phagocytosis were evaluated. Results: In TP, the counts of immature neutrophils were significantly increased vs. HV. The numbers of mature and CD62L^dim neutrophils remained unchanged but the production of ROS was significantly enhanced in TP vs. HV and the stimulation with fMLP significantly increased the generation of ROS in the mature and CD62L^dim neutrophils of HV. The counts of phagocyting neutrophils did not change but the mean phagocytic capacity showed an increasing trend in TP. In TP, the monocytes shifted toward the intermediate phenotype, whereas the classical and non-classical monocytes became less abundant. ROS generation was significantly increased in all monocyte subsets in TP vs. HV and PMA stimulation significantly increased those level in both, HV and TP. However, the PMA-induced mean ROS generation was significantly lower in intermediate monocytes of TP vs. HV. Sorting of monocyte and neutrophil subsets revealed a significant increase of ROS and decrease of phagocytic capacity vs. whole blood analysis. Conclusions: Neutrophils and monocytes display a phenotypic shift following severe injury. The increased functional abnormalities of certain subsets may contribute to the dysbalanced immune response and attenuate the antimicrobial function and thus, may represent a potential therapeutic target. Further studies on isolated subsets are necessary for evaluation of their physiological role after severe traumatic injury.

Polytrauma and concomitant hemorrhagic shock can lead to intestinal damage and subsequent multiple organ dysfunction syndrome. The intestinal fatty acid-binding protein (I-FABP) is expressed in the intestine and appears quickly in the circulation after intestinal epithelial cell damage. This porcine animal study investigates the I-FABP dynamics in plasma and urine after polytrauma. Furthermore, it evaluates to what extent I-FABP can also act as a marker of intestinal damage in a porcine polytrauma model. Eight pigs (Sus scrofa) were subjected to polytrauma which consisted of lung contusion, tibial fracture, liver laceration, and hemorrhagic shock followed by blood and fluid resuscitation and fracture fixation with an external fixator. Eight sham animals were identically instrumented but not injured. Afterwards, intensive care treatment including mechanical ventilation for 72 h followed. I-FABP levels in blood and urine were determined by ELISA. In addition, immunohistological staining for I-FABP, active caspase-3 and myeloperoxidase were performed after 72 h. Plasma and urine I-FABP levels were significantly increased shortly after trauma. I-FABP expression in intestinal tissue showed significantly lower expression in polytraumatized animals vs. sham. Caspase-3 and myeloperoxidase expression in the immunohistological examination were significantly higher in the jejunum and ileum of polytraumatized animals compared to sham animals. This study confirms a loss of intestinal barrier after polytrauma which is indicated by increased I-FABP levels in plasma and urine as well as decreased I-FABP levels in immunohistological staining of the intestine.