Systemic IL-17 after severe injuries. 
IL-17 is a cytokine produced by a newly identified T-cell subpopulation (THl7/THIL-17).  It is a central mediator in inflammatory processes that connects T-cell stimulation with neutrophil mobilization.  The role of IL-17 in the immune dysfunction after polytrauma is still not clarified.  In a retrospective study, the systemic concentration of IL-17 and IL-6 of 71 polytraumatized patients were analyzed daily by enzyme-linked immunosorbent assay.  The patients' collective consist of 55 men and 16 women (43 +/- 16 years; injury severity score, 33 +/- 13).  In only 6% of the patients, an increase in systemic IL-17 was detected.  In most patients (94%), no systemic IL-17 was detectable or the IL-17 concentrations in plasma were in the range of the healthy donor group.  To identify a possible role of systemic IL-17 in the posttraumatic phase, the patients were divided into two groups.  Group A (47 men, 15 women) consists of patients with IL-17 concentrations in the range of normal healthy donors.  Group B (8 men, 1 woman) consists of patients with elevated (>45 pg ml(-1) on at least 3 consecutive days) systemic IL-17 concentrations.  Three patients in group B showed highly increased systemic IL-17 concentrations (median, >200 pg mL(-1)).  These patients were male and showed all blunt chest and abdominal trauma with lung contusion and pneumohemothorax.  However, there was no conformity in other injury patterns, injury severity score, age, outcome, intensive care period, or clinical complications.  After a period of 4 years, we were able to obtain a new blood sample from one patient with high IL-17 level.  The systemic IL-17 value of this former patient was now less than the detection limit.  However, stimulation of peripheral blood mononuclear cells from thlise patient revealed elevated numbers of cells with the capacity to produce IL-17 as determined by enzyme-linked immuno spot assay and flow cytometry compared with peripheral blood mononuclear cells obtained from current polytrauma patients and healthy donors.  In conclusion, IL-17 is not suitable as a pathophysiological or predictive marker after polytrauma.  Whether highly increased systemic IL-17 concentrations detected in single patients are due to individually increased numbers of TH17 cells as we have demonstrated with one rerecruited patient has to be further analyzed.