Suppression and recovery of LPS-stimulated monocyte activity after trauma is correlated with increasing injury severity: a prospective clinical study.

Background: Monocytes represent a key immunocompetent cell type, whose functional capacity is profoundly influenced by systemic trauma. Because data on monocyte function in a heterogeneous trauma population, including slightly injured patients, is limited, we evaluated whether the magnitude of monocyte dysfunction can be related with injury severity and is useful as a predictive biomarker for development of systemic inflammatory response syndrome (SIRS) and sepsis.
Methods: Blood samples were obtained from 58 patients at admission to a level 1 Trauma Unit (mean injury severity score [ISS] of 25.7; range 4-75), and daily for five successive days. Monocyte activity was assessed by measuring lipopolysaccharide (LPS)-stimulated interleukin (IL)-1-beta production. Levels of IL-6, IL-10, and procalcitonin were also determined and values were correlated to injury severity and occurrence of SIRS.
Results: Even mildly injured individuals (ISS 1-8) showed a significant suppression of the LPS-response directly upon admission (p < 0.05). Both LPS-response (p = 0.049) and IL-6 levels (p = 0.046) were found to be predictive for the presence/diagnosis of SIRS. After minor trauma (ISS 1-8), the LPS-response returned to normal levels by day 2, whereas in more severely injured patients (ISS > or = 25) the suppression of monocyte activity persisted for the duration of the study period.
Conclusion: The extent of suppression of monocyte function is directly associated with the severity of trauma in both severely injured and patients with minor trauma. Acute posttraumatic changes in monocyte function and IL-6 concentrations were both predictive for the development of SIRS/sepsis. Although monocyte function in mildly injured patients is restored shortly after injury, the observed delay in recovery in severely traumatized patients may critically influence the clinical course.