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BackgroundThe immune response to trauma has traditionally been modeled to consist of the systemic inflammatory response syndrome (SIRS) followed by the compensatory anti-inflammatory response syndrome (CARS). We investigated these responses in a homogenous cohort of male, severe blunt trauma patients admitted to a University Hospital surgical intensive care unit (SICU). After obtaining consent, peripheral blood was drawn up to 96 hours following injury. The enumeration and functionality of both myeloid and lymphocyte cell populations were determined.ResultsNeutrophil numbers were observed to be elevated in trauma patients as compared to healthy controls. Further, neutrophils isolated from trauma patients had increased raft formation and phospho-Akt. Consistent with this, the neutrophils had increased oxidative burst compared to healthy controls. In direct contrast, blood from trauma patients contained decreased naïve T cell numbers. Upon activation with a T cell specific mitogen, trauma patient T cells produced less IFN-gamma as compared to those from healthy controls. Consistent with these results, upon activation, trauma patient T cells were observed to have decreased T cell receptor mediated signaling.ConclusionsThese results suggest that following trauma, there are concurrent and divergent immunological responses. These consist of a hyper-inflammatory response by the innate arm of the immune system concurrent with a hypo-inflammatory response by the adaptive arm.

The present study sought to examine the function of membrane lipid rafts in adherence-dependent oxidant production in human neutrophils. Rafts are membrane domains that are rich in glycosphingolipids and cholesterol and are thought to be the foci for formation of signaling complexes in a variety of cells. Disruption of lipid rafts by depletion of membrane cholesterol with the chelating agent methyl-beta-cyclodextrin (MbetaCD) has been widely used to examine the function of lipid rafts. Here, we report that treatment of human neutrophils with MbetaCD unexpectedly caused priming of these cells, manifested as enhanced adherence-dependent oxidant production. Treatment of neutrophils with MbetaCD dose-dependently increased oxidant production after adhesion to fibronectin-coated plates. This priming effect was associated with recruitment of CD11b- and CD66b-rich raft domains from the specific granules, as determined by immunoblot and flow cytometry. Confocal microscopy showed that MbetaCD caused otherwise untreated neutrophils to rapidly adhere and spread on fibronectin-coated plates. Furthermore, three-dimensional reconstruction microscopy studies showed that MbetaCD caused expansion and coalescence of raft domains that covered most of the cell surface. These large raft domains expressed CD11b primarily in the core of these regions. Our studies demonstrate that cholesterol depletion with MbetaCD results in neutrophil priming manifested as enhanced adherence-dependent oxidant production. These studies caution against assumption that any observed MbetaCD effects are a function of reduced raft formation.

Background: In response to traumatic injury or infection, human neutrophils are directed to the site of injury or infection by CXC chemokines that signal via 2 receptors, CXCR-1 and CXCR-2. In vitro studies have shown preferential loss of CXCR-2 expression and function after exposure to interleukin 8, N-formyl-methionylleucyl-phenylalanine (fMLP), C5a, and tumor necrosis factor ␣. Hypothesis: CXCR-2 expression and function are preferentially down-regulated in severely injured patients. Methods: We studied 20 patients within 24 hours of admission to the hospital. Patients with head injuries were excluded. Injury Severity Scores (range, 1-50; mean, 35) were calculated for each patient. To determine expression of CXCR-1 and CXCR-2, flow cytometry was used. Intracellular calcium mobilization and neutrophil migration to 10 nmol of interleukin 8, growth-related on-cogene ␣, and fMLP was measured to determine receptor function. Results: Compared with CXCR-1, there is a greater loss of CXCR-2 receptor expression in the severely injured group (P = .01). Neutrophils from patients with Injury Severity Scores greater than 16 did not mobilize calcium in response to growth-related oncogene ␣. However, there was no loss of calcium mobilization to interleukin 8 or fMLP. Chemotaxis to various stimulants is decreased in all injury groups. Conclusions: CXCR-2 expression and function are preferentially down-regulated in severely injured patients. Our data suggest that there are multiple mechanisms, in addition to receptor down-regulation, that play a role in the loss of migration and calcium flux in human neutrophils after injury.