gms | German Medical Science

Objectives: Phagocytosis by granulocytes and monocytes plays a fundamental role in immunological defense against pathogens and clearance of cellular debris after tissue injury due to trauma. According to the "two-hit hypothesis", the innate immune system including these cells is primed due to/after severe trauma. Subsequently, a secondary, even less strong stimulus may lead to an exaggerated immune response. This immune dysfunction often ends in serious infectious complications such as sepsis and/or (multiple) organ failure (MOF) in the later clinical course. The post-injury outcome including complications depends on trauma injury pattern, also. Here, we investigated the phagocytosis capacity of leukocytes and its correlation to trauma injury pattern.

Methods: Peripheral whole blood was taken daily from 29 severe trauma patients (TP, Injury Severity Score, ISS > 15) for ten days (1-10) following admission to the emergency department (ED). Fifteen healthy volunteers served as controls (HV). Samples were incubated with opsonized Staphylococcus aureus, which were labelled with pHrodo fluorescent reagent, and the percentage of phagocytic activity was assessed by flow cytometry. According to the Abbreviated Injury Scale (AIS) > 2 of head, chest or extremities the patients were divided into corresponding groups for injury pattern analysis.

Results: The mean distribution of phagocytic leukocytes at ED represented by 28.6±1.5% granulocytes, 59.3±1.9% monocytes and 12.1±0.8% lymphocytes in TP was comparable to HV (31.5±1.6% granulocytes, 60.1±1.6% monocytes and 9.7±0.9% lymphocytes). Comparing the distribution of phagocytic leukocytes in TP, the percentage of granulocytes increased significantly after D2 (39.1±1.2%, p<0.05), while the percentage of monocytes (52.0±1.2%, p<0.05) decreased after D2. This alteration persisted during the whole time course. The phagocytic activity of granulocytes (27.9±2.8%) and monocytes (55.2±3.3%) was significantly decreased at ED compared to HV (42.4±4.1% and 78.1±3.1%, respectively, p<0.05). After D2 up to D10, the phagocytic activity was significantly enhanced in granulocytes. The phagocytic activity of monocytes remained decreased on D1 and raised continuously to values comparable to ctrl during the ten days time course. There were no significant differences in the phagocytic activity of the cell subsets with regard to injury pattern.

Conclusion: Our data demonstrate that the increasing percentage of phagocytic granulocytes may indicate an enhanced mobilization out of bone marrow persisting until post-injury day 10. Furthermore, an initially decreased phagocytic activity of granulocytes is strongly increased in the 10-days post-injury course, data confirming the "two-hit hypothesis" after trauma. Interestingly, the altered activity of phagocytes after injury appeared not dependent on trauma injury pattern, but rather as a general characteristic of phagocytes after severe trauma.