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*
Department of Surgery, Klinikum rechts der Isar, and
Institute for Medical Microbiology, Immunology, and Hygiene, Technische Universität, Munich, Germany
| Abstract |
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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. | Introduction |
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Biologically active IL-12 is a heterodimeric cytokine that is comprised
of covalently linked p35 and p40 subunits and is produced by
phagocytes, dendritic cells, and B lymphocytes in response to bacteria,
bacterial products, intracellular parasites, or the ligation of cell
surface CD40 (10, 11). IL-12 is required for the production of IFN-
by NK cells and T lymphocytes and supports the development of the Th 1
phenotype of CD4+ T cells. IL-12 also enhances the
cytotoxic activity of activated NK cells and supports the generation of
cytolytic T lymphocytes. IFN-
enhances IL-12 release by phagocytes,
thereby inducing positive feedback interactions that are crucial for
the activation of the phagocyte system and T cell differentiation.
Thus, IL-12 is required for the immediate defense mechanisms of the
innate immune system as well as for the induction of subsequent
adaptive immune responses.
In contrast to its protective functions, an important role of IL-12 has also been described in several Th1-mediated autoimmune diseases, including experimental allergic encephalomyelitis, type I diabetes, and hapten-induced colitis (11). In mice that were sensitized by mycobacterial infection, IL-12 has been identified as a critical mediator of endotoxic shock; the administration of IL-12 is in itself sufficient to prime animals for enhanced mortality from endotoxin or TNF challenge (12, 13, 14). Therefore, studies in murine models indicate that IL-12 functions as a dichotomous immune regulator, playing important protective roles in immune defense but also exhibiting adverse functions in immune pathology.
In the present study, we investigated whether the capacity of monocytes to produce inflammatory cytokines may affect susceptibility to sepsis in patients undergoing major surgery. The results demonstrate that monocyte IL-12 secretion was significantly impaired before surgery in patients developing postoperative sepsis and indicate that IL-12 may be crucial for establishing a protective immune response against postoperative infection.
| Materials and Methods |
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Patients that had been admitted to the surgical intensive care
unit following major elective surgery of the upper and lower
gastrointestinal tract were included in a prospective study from June
1995 to March 1997. The clinical profiles of all of the patients
analyzed are detailed in Table I
. Patients
subjected to neoadjuvant radio- or chemotherapy, patients with acquired
or inherited immunodeficiencies, and patients receiving
immunosuppressive medication were excluded from this study. The study
group consisted of 184 patients; 165 patients had uneventful
postoperative recovery, and 19 patients developed septic complications.
Venous blood samples were collected from each patient at least 1 day
before the operation as well as on days 1 and 4 after surgical
intervention. Established criteria were used for the inclusion of
patients in the group with sepsis (15). Severe sepsis was defined as
sepsis associated with organ dysfunction, hypoperfusion, or hypotension
(15). Our study received local hospital ethical committee approval.
Informed consent was obtained from patients in all cases.
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PBMCs were isolated from 25 ml of heparinized blood using
Ficoll-metrizoate density gradient centrifugation, and monocytes were
purified by plastic adherence. Cytokine production of duplicate
cultures of 2 x 104 monocytes/well was stimulated by
incubation with 1 µg of endotoxin from Escherichia coli
serotype 0127:B8 (Sigma, St. Louis, MO) in 1 ml of RPMI 1640 medium
supplemented with 10% FCS for 16 h. Supernatants were centrifuged
to remove residual cells and stored at -20°C. The levels of IL-12
p70 heterodimer (Biermann, Bad Nauheim, Germany), TNF-
, IL-1ß, and
IL-10 (Medgenix Diagnostics, Fleurus, Belgium) in the supernatants of
stimulated monocytes or serum were determined by ELISA according to the
manufacturers instructions. All cytokine assays were standardized by
including a titration of the appropriate purified recombinant cytokine
of known concentration. The sensitivity levels of the ELISA assays were
5 pg/ml for IL-12 p70, 2 pg/ml for IL-1ß, 3 pg/ml for TNF-
, and 1
pg/ml for IL-10. The absorbance of the samples was determined on an MRX
microplate reader (Dynatech, Denkendorf, Germany) using 450 nm as the
primary wave length and 630 nm as the reference wave length.
Statistical analysis
A statistical analysis of the data was performed using the
Mann-Whitney U test, the Student t test, or the
2 test where appropriate. The level of significance was
set at p < 0.05.
| Results |
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secretion in sepsis patients was significantly elevated before
surgery and on postoperative day 1, levels of TNF-
on postoperative
day 4 were comparable with those of patients showing uneventful
postoperative recovery (Fig. 1
did not
correlate with sepsis severity (Fig. 2
were observed in patients with severe sepsis and in sepsis
patients that did not develop organ injury. Together, these results
indicate a preferential suppression of IL-12 production and exclude a
general defect in monocyte cytokine secretion in patients developing
sepsis after major surgery. The secretion of IL-12 p70 by the monocytes of cancer patients and of patients with nonmalignant disease in the uneventful recovery group was compared to address the question of whether reduced IL-12 production may reflect a cancer-associated immune defect. However, the results did not reveal any significant differences during the entire observation period (data not shown). Therefore, these results demonstrate that the suppression of monocyte IL-12 secretion does not occur as a consequence of malignant disease.
In additional experiments, the serum levels of IL-10 were determined to investigate whether the suppression of monocyte IL-12 p70 secretion may result from exposure to high levels of systemic antiinflammatory cytokines. The results of these studies clearly showed, however, that systemic levels of IL-10 were not increased in sepsis patients as compared with patients with uneventful recovery during the entire observation period (data not shown).
| Discussion |
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The inhibition of IL-12 by neutralizing Abs or the disruption of
the IL-12 gene strongly suppresses resistance against numerous
pathogens, while the administration of IL-12 appears to exhibit
protective effects (19, 20, 21, 22, 23, 24, 25, 26, 27). The results of the present report
establish a direct correlation between monocyte IL-12 production and
the development and severity of postoperative sepsis. To corroborate
these findings, the role of IL-12 in sepsis was further investigated
using an experimental model of abdominal sepsis (28). Abdominal
infection was induced by implanting a stent of a defined diameter into
the ascending colon of wild-type or IL-12 p40 knockout mice, and
survival was monitored for 14 days. The results revealed that IL-12
deficiency significantly reduced survival from bacterial peritonitis
(K. Pfeffer, S. Maier, M. Entleutner, N.Z., and C.D.H., unpublished
observations). Moreover, mice deficient for the IFN-
R were found to
be highly susceptible to experimental peritonitis (28). The results of
a recent study showing that burn injury suppresses splenocyte IL-12
release, and that the treatment of burn animals with IL-12
significantly reduces mortality from septic peritonitis are consistent
with our findings (29). Taken together, these results support the idea
that early production of IL-12 is required for resistance to bacterial
peritonitis. Thus, the results from our clinical study are supported by
animal models of peritonitis suggesting that the increased incidence
and prognosis of septic complications in patients with defective
monocyte IL-12 production results from the suppression of both innate
and T cell-dependent defense mechanisms.
It has been demonstrated that monocyte IL-12 secretion may be
suppressed by exposure to antiinflammatory cytokines such as IL-10 and
by endotoxin desensitization protocols (10). In addition, the ligation
of phagocyte complement receptor type 3 (Fc
) or scavenger receptors
and the incubation of monocytes with IFN-
ß or IL-11 was shown to
inhibit the production of IL-12 (30, 31, 32, 33). Whereas treatment with IL-10
reportedly results in a general suppression of monocyte cytokine
secretion involving IL-1, TNF, IL-6, IL-8, granulocyte CSF, and
granulocyte-macrophage CSF, the inhibitory effects of IL-11, type I
IFNs, or macrophage receptor ligation appeared to be selective for
IL-12 (30, 31, 32). Our findings that IL-1ß production is only reduced
during the late postoperative course in patients developing
postoperative sepsis and that TNF-
release is even increased at
different time intervals before the onset of sepsis consequently
suggest that the suppression of monocyte IL-12 production may not be
mediated by IL-10. Consistent with this interpretation, systemic IL-10
levels were not increased either before surgery or during the
postoperative course in patients developing sepsis. Moreover, increased
TNF-
secretion before surgery and on postoperative day 1 argues
against elevated monocyte production of immunosuppressive mediators
such as IL-10. The role of phagocyte receptors, IL-11, or type I IFNs
for the suppression of IL-12 secretion in surgical patients, however,
remains to be determined.
The results presented in this report are consistent with the concept that immunosuppression predisposes patients undergoing major surgery for the development of septic complications. We demonstrate that low preoperative IL-12 secretion by monocytes precedes the onset of sepsis and identifies patients that are at high risk for severe postoperative sepsis. Thus, defective monocyte IL-12 secretion before surgery appears to be associated with the hyporeactive state of the immune system and may consequently allow for the stratification of patients for novel therapeutic strategies aimed at the preoperative stimulation of host defense mechanisms. In conjunction with immune modulation, the infection rate in patients with low preoperative monocyte IL-12 secretion may be reduced by less aggressive surgical procedures that are associated with fewer complications, by split operations applying second-step reconstruction procedures following initial resection, or by alternate regimens of tumor therapy.
| Acknowledgments |
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| Footnotes |
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2 Address correspondence and reprint requests to Dr. Bernhard Holzmann, Department of Surgery, Klinikum rechts der Isar, Technische Universität, Ismaninger Str. 22, D-81675 Munich, Germany. E-mail address: ![]()
Received for publication December 2, 1997. Accepted for publication May 8, 1998.
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