Interleukin-18 concentration in the peritoneal fluid correlates with the severity of peritonitis

Background Interleukin (IL)-18 is a novel cytokine that has recently been characterized as an inducer of interferon-gamma (IFN-γ). The aim of this study was to investigate the clinical significance of peritoneal IL-18 concentrations in patients with peritonitis. Methods We measured IL-18, IFN-γ, and IL-10 concentrations in the peritoneal fluid of 28 patients undergoing laparotomy for peritonitis. Correlations between the peritoneal cytokine concentrations and the severity of illness determined by systemic inflammatory response syndrome (SIRS) criteria, Acute Physiological and Chronic Health Evaluation II (APACHE II) score, peritoneal fluid bacterial culture results, subsequent development of organ failure, and length of hospital stay were assessed. Results Interleukin-18 concentration was significantly increased in patients who developed SIRS, in those with culture-positive peritonitis, and in those who developed organ failure, as compared with the other patients. Interleukin-10 concentration, which was also significantly increased in patients with culture-positive peritonitis, showed a close correlation with IL-18 concentration. Although a weak correlation was observed between IL-18 and IFN-γ concentrations, IFN-γ concentrations did not show any association with patients’ clinical parameters. However, the IFN-γ/IL-18 ratio was significantly lower in patients with an APACHE II ≥10, and in those with culture-positive peritonitis, as compared with the other patients. Conclusions Peritoneal IL-18 concentration increased in response to intraperitoneal bacterial infection and seemed to reflect the severity of peritonitis. However, the capacity of IL-18 to produce IFN-γ may be altered depending on the severity of peritonitis.