Infect Immun 70(8): 4441-4446

Interleukin-10 Controls the Onset of Irreversible Septic Shock

Division of Pediatric Pharmacology and Critical Care Medicine, Department of Pediatrics,^{Department of Medicine, Pathology, and Pharmacology, Case Western Reserve University School of Medicine, Cleveland, Ohio 44106-4952}²

^{Corresponding author. Mailing address: Department of Medicine, Case Western Reserve University School of Medicine, 10900 Euclid Ave., Cleveland, OH 44106-4952. Phone: (216) 368-1668. Fax: (216) 368-1674. E-mail:}ude.urwc.op@4lda.

Received 2002 Apr 3; Accepted 2002 Apr 29.

Abstract

Lethality from sepsis is believed to be mediated by a proinflammatory cytokine cascade, yet blocking the proinflammatory cytokines tumor necrosis factor alpha (TNF-α) and interleukin-1 (IL-1) fails to prevent mortality in human disease and a mouse model of sepsis induced by cecal ligation and puncture (CLP). The role of the antiinflammatory cytokine IL-10 in the CLP model of sepsis is unclear, with either protective or harmful effects demonstrated, depending upon the time of intervention. We therefore hypothesize that IL-10 functions as a temporal regulator of the transition from early reversible sepsis to the late phase of irreversible shock. Transition from reversible sepsis to irreversible shock in the CLP model was defined as the time when removal of the necrotic cecum by rescue surgery is no longer effective. We subjected IL-10-deficient (IL-10^{) and wild-type (IL-10}^{) mice to CLP and monitored the progression of sepsis, the onset of irreversible shock, and mortality. Onset of lethality in IL-10}^{mice occurred significantly earlier than in IL-10}^{mice and was associated with 15-fold-higher serum levels of TNF-α and IL-6. Consistent with these findings, the efficacy of rescue surgery after lethal CLP is lost 10 h earlier in IL-10}^{mice than in IL-10}^{mice. Treatment with recombinant human IL-10 5 h after CLP significantly improved survival and lengthened the therapeutic window for rescue surgery in both strains of mice. These results demonstrate that IL-10 controls the onset of irreversible septic shock after CLP.}

Abstract

Sepsis is a major cause of morbidity and mortality in our hospitals (2). A severe and uncontrolled systemic inflammatory response triggered by an invading microbe may lead to evolving multiorgan dysfunction (7). Occasionally, despite appropriate treatment and support of the septic patient, death may still ensue if irreversible damage occurs to vital organs. The onset of this irreversible shock is not easily defined clinically, nor are the mechanisms regulating this transition known. Cytokines may be important mediators in the development of this lethal multiorgan damage. For example, inflammatory cytokines, such as tumor necrosis factor alpha (TNF-α), interleukin-1 (IL-1), and IL-6, are elevated in the sera of both adult and pediatric septic patients (6, 9, 20, 29) and affect symptoms such as hypotension, fever, and the production of acute-phase proteins (21). However, the contribution of these proinflammatory cytokines in directly mediating mortality from sepsis is not clear, since therapies utilizing neutralizing antibodies or soluble receptor antagonists against TNF-α and IL-1 fail to show a significant benefit in outcome for patients with sepsis (5, 13). Possible explanations for the clinical failure of these cytokine-targeted therapies may be that the antibodies or antagonists were administered too late or that other unopposed inflammatory mediators continue to support the disease process.

In contrast to humans, the use of anticytokine therapies against TNF-α (4) and IL-1 (22) in a murine model of endotoxemia leads to dramatic improvement in animal mortality. When lipopolysaccharide (LPS), the endotoxin from gram-negative bacteria, is injected into susceptible animals a rapid systemic inflammatory cascade is initiated in the absence of bacteremia. The lack of ongoing injury after a single administration of endotoxin and the absence of bacteremia in this model highlight its artificial nature and may explain why many clinical trials, based on observations with this model, have failed. The kinetics and magnitude of cytokine production in LPS-induced sepsis are also dramatically different from that seen in a more clinically relevant model of peritonitis with bacteremia induced by cecal ligation and puncture (CLP) (25), which closely mimics the human disease of septic shock (14). In sepsis induced by CLP, neutralizing antibodies to TNF-α are not protective against mortality (10), and C3H/HeJ mice that are resistant to the lethal effects of LPS are still susceptible to mortality from CLP (19). These differences between the LPS and CLP models suggest that the immunology of sepsis is far more complex than the cascade of events activated by endotoxin and that the exact role of proinflammatory cytokines as mediators of mortality is unclear.

Besides stimulating the synthesis of proinflammatory cytokines, the septic response in patients and animal models also results in the production of antiinflammatory mediators, such as IL-10 (8, 11, 30, 31). IL-10 is a 35-kDa homodimeric protein, produced primarily by monocytes, T cells, and B cells, that inhibits the production of proinflammatory cytokines in vitro (16). IL-10 is completely protective in the LPS model of sepsis (3, 15), but in the CLP model the administration of neutralizing antibodies to IL-10 at the time of CLP only partially exacerbates mortality (28, 31). However, inhibition of IL-10 12 h after CLP actually improves survival (28). Thus, in this model IL-10 can be either protective or harmful depending on the time of intervention. We therefore postulate that IL-10 regulates the transition from reversible sepsis to irreversible shock. In the CLP model we define this transition as the time point when removal of the necrotic cecum by rescue surgery is no longer effective. Here we report the ability of IL-10 to regulate the progression of sepsis and control the onset of irreversible shock and mortality in the CLP model.

Acknowledgments

We thank Scott Fulton for providing the tribromoethanol anesthetic, David Spencer, Doug Kou, Robin Jump, and Kelly Miller for their technical assistance. Critical discussions and review of the manuscript by Giovanni Latella, Fred Heinzel, Leslie T. Webster, Jr., and Jeffrey L. Blumer are much appreciated.

This study was supported by grants HD-31323 (Jeffrey L. Blumer, Department of Pediatrics, Case Western Reserve University, Cleveland, Ohio) and CA-77717 (A.D.L.) from the NIH.

Acknowledgments

Notes

Editor: A. D. O'Brien

Notes

Editor: A. D. O'Brien

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