Department of Traumatology and Harald Tscherne Research Laboratory, University Hospital Zurich, Raemistraße 10, 8032, Zurich, Switzerland.
Department of Orthopaedic Trauma and Reconstructive Surgery, University of Aachen Medical Center, Pauwelsstraße 30, 52074, Aachen, Germany.
Pathol Res Pract. 2020 Oct;216(10):153108. doi: 10.1016/j.prp.2020.153108. Epub 2020 Jul 12.
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.
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.
Neutrophil numbers were significantly reduced at 3 days compared with baseline measurements (1.2 × 10 vs. 6.3 × 10 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/CD11a-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.
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/CD11a) 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.
股骨骨折及骨折固定后免疫反应过度激活与全身和局部并发症的发生有关，尤其是多发创伤患者。循环中性粒细胞（最常见的免疫细胞）功能失调被认为是这些不良创伤后病程的中心病理生理基础。我们的目的是研究股骨干骨折并髓内固定后循环中性粒细胞表面受体动力学的活性和功能变化。
在 18 只 Sprague-Dawley 大鼠中诱导髓内固定后的股骨干骨折。动物在不同时间点终止，即 3 天（n = 5，第 3 组）、7 天（n = 5，第 7 组）和 14 天（n = 5，第 14 组），并相应分组。此外，在每组 1 只对照动物（n = 3）麻醉诱导和终止后进行基线测量，不进行髓内钉固定和骨折诱导。比较各组间循环中性粒细胞的数量和细胞表面表达的 CD11b、CD11a、CD62L 和 CD49d。
与基线测量相比，第 3 天中性粒细胞数量显著减少（1.2×10 比 6.3×10 细胞/ml，p < 0.01）。第 7 天，中性粒细胞计数显著恢复至基础水平（p < 0.05）。第 3 天，CD11b 表达明显降低，而 CD11a 表达增加（p < 0.05）。第 7 天，循环中性粒细胞池表现出一种独特的 CD11b/CD11a-中性粒细胞亚群，CD49d 的共表达显著增加。与基线测量相比，CD62L 的表达在整个实验过程中没有明显变化。
本研究首次表明，髓内固定的股骨干骨折与循环中性粒细胞计数的暂时减少以及循环中性粒细胞功能的变化有关。此外，我们还发现，中性粒细胞激活状态恢复到基础水平与循环中新型中性粒细胞亚型（CD11b/CD11a）的出现同时发生。我们关于创伤后循环中性粒细胞计数和功能变化的基本新发现为进一步阐明中性粒细胞作为不同创伤后过程的激活剂和调节剂的作用提供了极好的基础，可能导致局部（如骨折愈合障碍）或全身（如 MODS）并发症。这可能导致开发特定的治疗方法来减少创伤后的不良后果。
