Increased susceptibility to postoperative sepsis in patients with impaired monocyte IL-12 production.

IL-12 is a potent immunoregulatory cytokine that is essential for the development of protective immunity, as demonstrated by numerous animal models of infection. Here, we provide evidence for a critical role of IL-12 in human sepsis. The results of a prospective study of 184 patients undergoing major elective surgery of the upper and lower gastrointestinal tract revealed that, in contrast to patients showing uneventful recovery, monocyte IL-12 production was severely and selectively impaired in patients developing postoperative sepsis. Moreover, the extent of monocyte IL-12 suppression correlated with the severity of postoperative sepsis. Monocyte IL-12 secretion was suppressed before surgery and remained low until the onset of sepsis. Therefore, the suppression of IL-12 secretion preceded the onset of postoperative sepsis but did not occur as a consequence of major surgery. In contrast, IL-1beta production was only reduced during the late postoperative course in patients developing postoperative sepsis, and TNF-alpha release was even increased at different time intervals before the onset of sepsis. Thus, reduced IL-12 release does not reflect a general defect in monocyte cytokine production. Consequently, these results establish a critical role for IL-12 in early resistance to postoperative infection and may allow for the development of novel therapeutic strategies designed to stimulate host defense mechanisms and to reduce the incidence and severity of septic complications.