gms | German Medical Science

Objectives: Patients suffering severe trauma are undergoing critical immunomodulation, increasing the risk of post-traumatic complications. Extracellular vesicles (EVs) have been shown to highly affect the post-traumatic inflammatory response. Therefore, our aim in this study was to investigate the impact of circulating EVs on PBMC differentiation, as they are crucial modulators of inflammation.

Methods: Male Sprague-dawley rats (14 weeks old) underwent blunt chest trauma, hemorrhagic shock and femoral fracture with subsequent internal (IF) or external fixation with change to IF (E-IF) after 6 days. Sham animals underwent analgosedation only. Blood was taken 72 hours and 7 days after the initial trauma. EVs were isolated by plasma-centrifugation. Circulating PBMCs were obtained from healthy rats by density centrifugation methodology. The cells were incubated with EVs from different groups or no EVs (control) for 24 hours. An additional group underwent stimulation with lipopolysaccharide (LPS) after EV incubation, simulating a severe secondary inflammatory stimulus, as seen in posttraumatic bacterial infections. Cell differentiation was assessed via flow-cytometry and expression of CD3, CD45-RA, CD43, CD161 as fractions of single, viable CD45^pos leukocytes. Cellular ratios were compared using one-way ANOVA and Games-Howell or Tukey post-hoc Test.

Results: No significant difference was observed between IF and E-IF; thus, the groups were pooled as polytrauma group. T-cells were significantly increased in sham and polytrauma after stimulation with LPS. T-cells showed a trend to increase after incubation with polytrauma EVs compared to sham EVs in the 72 h hours group, with an even clearer trend in the 7 day polytrauma group. T-cells without EV incubation were significantly increased compared to incubation with sham EVs. B-cell population showed an inverse-correlating trend. Monocytes were significantly reduced by LPS stimulation in sham and polytrauma groups. This was not significantly affected by EV stimulation. Monocytes showed a trend to decrease after incubation with EVs from the 7 day polytrauma group compared to 7 day sham. There were no differences in M1 and M2 polarization of monocytes in any group.

Conclusion: Circulating EVs are potentially involved in maintaining an ongoing immune balance. After polytrauma, EVs might help to maintain this balance, while a further immune stimulator, as a bacterial infection, can lead to a cellular immune-dysregulation, potentially priming further complications.