Increased neutrophil migratory activity after major trauma: a factor in the etiology of acute respiratory distress syndrome?

OBJECTIVE: Neutrophil infiltration of the lung is characteristic of early posttraumatic acute respiratory distress syndrome (ARDS). This study examines the ability of neutrophils isolated (over the first 24 hrs) from the peripheral blood of patients admitted after major trauma to migrate in response to interleukin-8. Interleukin-8 is elevated in the lung within 2 hrs of major trauma in patients who later develop ARDS, and thus it plays a central role in the recruitment of neutrophils to the lung and their subsequent activation. We hypothesized that enhanced interleukin-8-mediated neutrophil migratory activity in the early postinjury phase, before the development of ARDS, may be a crucial factor in the etiology of ARDS.
DESIGN: Prospective observational study.
SETTING: University Hospital Wales, the Royal Gwent Hospital, and East Glamorgan General Hospital. Laboratory work was conducted at the Institute of Nephrology. PATIENTS: Adult blunt trauma victims with Injury Severity Score > or = 18.
MEASUREMENTS AND MAIN RESULTS: Neutrophils were isolated from citrated blood from 17 adult blunt major trauma patients at admission (0 hrs) and 8 and 24 hrs later. Identical samples were obtained from normal laboratory volunteers (n = 9). The neutrophil count in each specimen was measured, and the number of neutrophils migrating across porous tissue culture inserts in response to defined concentrations of interleukin-8 (0, 10, 30, and 100 ng/mL) was quantitated by peroxidase assay. Neutrophil counts in the whole blood specimens obtained from those later developing ARDS were elevated significantly at admission and declined rapidly throughout the next 24 hrs. Significantly greater numbers of trauma patients' neutrophils migrated to concentrations of interleukin-8 (30 and 100 ng/mL) at each time point when compared with normal volunteers (Mann-Whitney U test, p <.05). Neutrophils isolated from major trauma patients exhibited an enhanced migratory response to high concentrations of interleukin-8 throughout the first 24 hrs of admission, in contrast to the normal physiologic attenuation of migration seen in neutrophils isolated from normal laboratory volunteers.
CONCLUSIONS: These data indicate that major blunt trauma enhances the migratory capacity of circulating neutrophils. This is manifest within 2 hrs of admission and may be attributable to alteration in interleukin-8 receptor expression, affinity, or downstream signaling. In patients who later develop ARDS, initially elevated circulating neutrophil counts decrease rapidly, over the same time course. Early enhanced neutrophil migratory activity coupled with elevated pulmonary concentrations of interleukin-8 may be central to the establishment of the neutrophil infiltration that is characteristic of ARDS.