Phagocytizing activity of PMN from severe trauma patients in different post-traumatic phases during the 10-days...

Phagocytizing leukocytes (granulocytes and monocytes) play 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", phagocytes become primed due to/after trauma. Subsequently, a secondary stimulus may lead to their exaggerated response. This immune dysfunction can result in serious infectious complications, also depending on trauma injury pattern. Here, we investigated the phagocytizing capacity of leukocytes, and its correlation to trauma injury pattern.

Peripheral whole blood was taken daily from 29 severely injured trauma patients (TP, Injury Severity Score, ISS≥28) for ten days (1-10) following admission to the emergency department (ED). Sixteen healthy volunteers served as controls (HV). Samples were incubated with opsonized Staphylococcus aureus labelled with pHrodo fluorescent reagent and the percentage of phagocytizing activity was assessed by flow cytometry. Abbreviated Injury Scales (AIS)≥3 of head, chest and extremities were used for injury pattern analysis.

Overall distribution of active phagocytes (out of 100% phagocytizing leukocytes) in TP included granulocytes with 28.6±1.5% and monocytes with 59.3±1.9% at ED, and was comparable to HV (31.5±1.6% granulocytes and 60.1±1.6% monocytes). The percentage of phagocytizing granulocytes increased significantly after D2 (39.1±1.2%), while the percentage of phagocytizing monocytes (52.0±1.2%, p<0.05) decreased after D2. These changes persisted during the whole time course. Phagocytizing 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). After D2 up to D10, phagocytizing activity was significantly enhanced in granulocytes. Phagocytizing activity of monocytes remained decreased on D1 and has risen continuously during the ten days time course to values comparable to HV. No significant differences in phagocytosis could be associated to certain injury pattern.

Our data demonstrate that the increasing percentage of phagocytizing granulocytes may indicate their enhanced mobilization out of bone marrow persisting until post-injury day 10. Furthermore, an initially decreased phagocytizing activity of granulocytes is strongly increased in the 10-days post-injury course. The altered activity of phagocytes due to injury could not be linked to any trauma injury pattern, and emerged rather as a general characteristic of phagocytes after severe trauma.