Review Article

SHOCK, Vol. 28, No. 5, pp. 504Y517, 2007

Review Article THE INNATE IMMUNE RESPONSE TO SECONDARY PERITONITIS J.W. Olivier van Till, Suzanne Q. van Veen, Oddeke van Ruler, Bas Lamme, Dirk J. Gouma, and Marja A. Boermeester Department of Surgery, Academic Medical Center, University of Amsterdam, The Netherlands Received 29 Nov 2006; first review completed 19 Dec 2006; accepted in final form 19 Mar 2007 Downloaded from https://journals.lww.com/shockjournal by BhDMf5ePHKav1zEoum1tQfN4a+kJLhEZgbsIHo4XMi0hCywCX1AWnYQp/IlQrHD3atkqZ1vMSkVAc0sbmCnZGTercFikn7eqCapmC/7PjVw= on 09/11/2018

ABSTRACT—Secondary peritonitis continues to cause high morbidity and mortality despite improvements in medical and surgical therapy. This review combines data from published literature, focusing on molecular patterns of inflammation in pathophysiology and prognosis during peritonitis. Orchestration of the innate immune response is essential. To clear the microbial infection, activation and attraction of leukocytes are essential and beneficial, just like the expression of inflammatory cytokines. Exaggeration of these inflammatory systems leads to tissue damage and organ failure. Nonsurvivors have increased proinflammation, complement activation, coagulation, and chemotaxis. In these patients, anti-inflammatory systems are decreased in blood and lungs, whereas the abdominal compartment shows decreased neutrophil activation and decreased or stationary chemokine and cytokine levels. A later down-regulation of proinflammatory mediators with concomitant overexpression of anti-inflammatory mediators leads to immunoparalysis and failure to clear residual bacterial load, resulting in the occurrence of superimposed infections. Thus, in patients with adverse outcome, the inflammatory reaction is no longer contained within the abdomen, and the inflammatory response has shifted to other compartments. For the understanding of the host response to secondary peritonitis, it is essential to realize that the defense systems presumably are expressed differently and, in part, autonomously in different compartments. KEYWORDS—Abdominal sepsis, inflammation, host defense, immune response, peritonitis, pathophysiology

INTRODUCTION

separately, an overview of the inflammatory chain of events in clinical studies and experimental peritonitis models is lacking. This review focuses on molecular patterns of inflammation and related systems, and how these patterns form the host response to intra-abdominal infections and their complications. The data in this review have been extracted from both clinical studies and various experimental models. This may hamper comparability (8). However, in the absence of widely available clinical data on human peritonitis, the current review explores general patterns in peritonitis without the certitude of definite extrapolation because specific biologic phenomena are context dependent.

Secondary peritonitis continues to cause high morbidity and mortality. Despite remarkable developments in surgical and intensive care treatment, the average associated mortality rate of secondary peritonitis remains at nearly 30% (1, 2). Mortality ranges from less than 5% in low-risk patients to approximately 90% in high-risk patients, that is, septic patients with quadruple multiple organ failure (MOF) (3). During a 5-year period, diffuse peritonitis was the indication for operation in approximately 7% of all laparotomies (4). Secondary peritonitis is defined as peritoneal inflammation that follows intra-abdominal lesions such as anastomotic leakage, perforation of hollow viscus, and bowel necrosis, penetrating infectious or cancerous processes (4). Subsequent microbial contamination of the abdominal cavity leads to infection, which initiates the innate immune response (5). The primary host response to the invading microorganisms will be initiated by resident peritoneal macrophages (PM7) and mesothelial cells that are responsible for the primary phagocytosis and subsequent activation and recruitment of polymorphonuclear granulocytes (PMNs) and monocytes into the peritoneal cavity (6). Monocytes will rapidly differentiate, increasing the macrophage population (7). How and when this intra-abdominal infection develops into sepsis and MOF is still unclear. Although many different inflammatory mediators and systems have been studied

HOST DEFENSE SYSTEMS IN SECONDARY PERITONITIS Various soluble and membrane-bound factors mediate the concerted actions, which constitute the innate response to infections and tissue damage. Cytokines are small proteins (T8 Y 80 kDa) that have a central role in positive and negative regulation of immune responses and in integrating these reactions with other physiological systems such as the complement and hematopoietic systems. Cytokines act by binding to specific receptors at the target cell membrane, setting off a cascade that leads to induction, enhancement, or inhibition of a number of cytokine-regulated genes in the nucleus, thereby modulating the cell’s immunological activity. During peritonitis, several cytokines are secreted by reticuloendothelial cells, mesothelial cells, and PM7. IL-1" and TNF-! were the first cytokines to be identified as leading players and primary mediators of inflammatory response during experimental peritonitis (9, 10). Since their discovery,

Address reprint requests to Marja A. Boermeester, MD, PhD, Department of Surgery, Room G4-109.2, Academic Medical Center, Meibergdreef 9, 1105 AZ Amsterdam, The Netherlands. E-mail: [email protected]. DOI: 10.1097/shk.0b013e318063e6ca Copyright Ó 2007 by the Shock Society

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Copyright @ 2007 by the Shock Society. Unauthorized reproduction of this article is prohibited.

SHOCK NOVEMBER 2007 a variety of mediators have been identified, exerting many kinds of inflammatory functions in different compartments of the body (i.e., intra-abdominal, circulation, distant organs) in the host reaction to peritonitis. This chapter summarizes the function of mediators in various important events in the development of secondary peritonitis (i.e., leukocyte recruitment and activation, clearance of microorganisms, and coagulation). Mediators involved in leukocyte recruitment and activation

Chemotaxis—During the early stages of peritonitis, PMNs and activated mononuclear cells migrate to the abdominal cavity after an upstream gradient of chemoattractant cytokines. These chemokines can be generally subdivided into two groups: first, CC chemokines (with two adjacent cysteines near the amino terminus), for example, macrophage chemotactic protein 1 (MCP-1) and macrophage inflammatory protein 2 (MIP-2), which attract and activate mononuclear cells; and second, CXC chemokines (the equivalent two cysteine residues are separated by another amino acid), for example, IL-8, which attract and activate PMNs. Besides chemokines, the arachidonic acid metabolite leukotriene B4 (LTB-4) is also proven to be an important chemoattractant of neutrophils in peritonitis (11). Like prostaglandins, LTB-4 is an end product of hydrolysis of phospholipids and free fatty acids, initiated by phospholipase A2. Secretory phospholipase A2 is an acute-phase protein that has been seen to be produced locally by peritoneal neutrophils (12) and promoted bacterial clearance in peritoneal lavage fluid and in the spleen and liver (13). In one animal model, peritoneal concentrations of cytokineinduced neutrophil chemoattractant keratinocyte-induced chemokine (KC), a murine analog of IL-8, were higher than levels in plasma. This caused neutrophils to migrate from the circulation to the abdominal cavity (14). In an in vitro model with human peritoneal mesothelial cells, PMNs were seen to migrate toward a gradient of IL-8 (15). The production of these proteins was induced by early cytokines such as TNF-! and IL-1" (16, 17). The peritoneal lining of the abdominal cavity is composed of mesothelial cells that are shown to be a major source of these chemokines (18). Other resident peritoneal cells, including mast cells and PM7, were also proven to be a primary center of chemotactic activity. In experimental peritonitis, mast cells produced chemokines such as MCP-1, KC, and MIP-2 (19, 20). Macrophages exerted an inhibitory effect on peritoneal PMN recruitment and chemokine generation by production of IL10, which in turn inhibited the release of proinflammatory cytokines (21Y23). Surprisingly, histamine, one of the most important products of mast cells, decreased phagocytic recruitment and delayed bacterial clearance (24), although how the anti-inflammatory function of histamine operates is still unclear. Another anti-inflammatory cytokine, IL-13, seemed to share these anti-inflammatory functions during peritonitis (25). Chemokines have been proven to be instrumental in the influx of PMNs to remote organs in peritonitis. Diffusion of inflammatory mediators (IL-1", TNF-!) from the circu-

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lation (26) or transendothelial signaling (27) is thought to play an important role in the pulmonary activation of resident macrophages and monocytes. This caused the initial local inflammation and chemotaxis seen in peritonitis (28). Chemokine-induced recruitment of PMNs resulted in a further increased local chemokine gradient (MIP-2, IL-8) and inflammation (29, 30). In various polymicrobial models of peritonitis, the expression of MIP-2, KC, and MIP-1! was strongly increased in the lungs, indicating pulmonary migration of leukocytes (31, 32). Also, when phospholipase A2 (PLA2) was inhibited, pulmonary damage in experimental peritonitis was reduced because of inhibited pulmonary PMN sequestration, which can be attributed to reduced LTB-4 expression (33). Progressive induction of chemokine gene expression was observed in the kidneys accompanied by leukocyte accumulation and acute renal failure (34). The process of local end-organ inflammatory activation during peritonitis (Bcompartmentalization[) is discussed in detail in section 4 of this review. In summary, during peritonitis, expression of chemoattractants is increased in the abdomen but also in distant organs such as the lungs. This induces an influx of leukocytes after an upstream chemokine gradient. Adhesion/Transmigration—Adhesion molecules are needed to allow PMNs to transmigrate from the circulation into the abdominal cavity and into distant organs. Selectins participate in the early stages of PMN adhesion (rolling of PMN along the endothelium). L selectin is expressed on the PMN, whereas P and E selectins are expressed on the endothelium. During peritonitis, both E and P selectin expressions were increased in the vasculature of the intestines and other intraperitoneal organs (35, 36). Some experimental studies have shown that these selectins may also contribute to neutrophil migration into the lungs, although the results are variable. E and P selectins were both found to be increased in the lung (31, 36), but a reduced expression of E selectin was not associated with a decrease in PMN activation (37). P selectin deficiency in monomicrobial murine peritonitis did not interfere with PMN influx in the lung but decreased abdominal PMN accumulation (38). Selectin engagement biologically precedes firm adhesion of neutrophils to endothelial cells in an integrin-dependent manner. Integrins are transmembrane glycoproteins that mediate cell-cell and cell-matrix interaction and appear to play an important role in cell migration. "2-integrin transcription was induced by complement protein C5a during cecal ligation and puncture (CLP) peritonitis in rats (39). The "2-integrin CD11-CD18 complex was seen to be essential to pulmonary PMN infiltration in rabbit peritonitis (40). Polymorphonuclear granulocytes that express this complex strongly bind to endothelial cells that express intercellular adhesion molecules (ICAMs) 1 and 2. Mesothelial cells also produce these adhesion molecules (41). In Streptococcus pneumoniaeYinduced and CLP peritonitis, mice that were genetically deficient in ICAM-1 showed inhibited PMN influx into the abdomen (38, 42). Thus, ICAM-dependent adhesion may also play an important part in peritoneal PMN influx in peritonitis.


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In summary, peritonitis leads to the expression of adhesion molecules on the endothelium and PMN, initiating transmigration of PMN from the circulation into the abdominal cavity and the lungs. Mediators involved in the clearance of microorganisms

The ability to clear the intra-abdominal bacterial load is significantly associated with the outcomes of experimental peritonitis (43). Cecal ligation and puncture with prior cecal lavage had a 100% survival rate, emphasizing the importance of gut flora in the development of abdominal sepsis (44). TNF-! and IL-6 play a regulatory role in promoting local and systemic bacterial clearance (10, 17, 45), but the cytokine that seems to be most important for the antibacterial innate response during abdominal sepsis is IL-12 (46). This cytokine is produced primarily by monocytes and macrophages. In various models of peritonitis, it directly increased the cytolytic activity of mononuclear and polymorphonuclear cells by increasing NO production and microbicidal activities (47), and indirectly by augmenting the production of interferon (IFN) + and TNF-! (47Y49), which regulate bacterial phagocytosis. Natural killer cells participate in early local and systemic microbial eradication after activation by IL-12. Natural killer cells, together with PM7, were seen to be an important source of IFN-+ during peritonitis (50, 51). Interferon + induced T cells to exhibit a proinflammatory phenotype, augmenting both bacterial eradication and the local host response in general. IL-18 is a cytokine that directly affects PMN activation and, thus, also phagocytic capacity. In an Escherichia coli model of peritonitis, IL-18 knockout mice displayed an increased PMN influx to the peritoneal cavity. However, these cells were less activated and unable to adequately clear the bacteria (52). In contrast, in a polymicrobial peritonitis model, IL-18 was less important than IL-12 with respect to reduction of the abdominal bacterial load (47). Granulocyte colony-stimulating factor (G-CSF) is a cytokine with direct stimulatory effects on PMN activity. It enhanced both PMN maturation and proliferation, and also ensured chemotactic responses and phagocytosis, which in turn increased microbactericidal activities (53). The administration of G-CSF in peritonitis (with or without antibiotics) averted immunoparalysis, which is often a complication in peritonitis (54). G-CSF decreased the number of bacterial colony-forming units locally and in the lungs (54, 55). Phagocytosis and opsonization is also induced by complement protein C5a. The administration of immunoglobulin (Ig)G antibody to C5a in CLP rats produced increased bacterial load (56). The same effects can be seen in mice unable to activate the common pathway by blocking of the classical and the alternative pathway (by factor B and C2 genetic deletion) (57, 58). IL-10, which is also predominately produced by PM7, counteracted the positive effects on bacterial clearance of proinflammatory cytokines in peritonitis by inhibiting their expression (23). Impairment of IL-27 expression, a cytokine that activates anti-inflammatory pathways, enhanced PMN migration, oxidative burst capacity, and bacterial clearance (59). In human studies and clinical practice, bacterial load is effectively controlled by the use of antibiotics. In most

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experimental peritonitis models, often, no antibiotics are used, hindering comparability between experimental and clinical studies. However, in some experimental studies, the effects of antibiotics have been examined. These effects were beneficial to the outcome of peritonitis regardless of disease severity (60). For example, CLP mice had reduced overall mortality with decreased plasma and peritoneal levels of TNF-! and IL-6 after i.p. antibiotic use (imipenem or ciprofloxacin/ clindamycin) (61). The inflammatory response in the lungs was also reduced by antibiotic treatment, exemplified by reduced TNF-! and IL-1" mRNA and reduced MPO levels, after continuous cefoxitin, metronidazole, or aztreonam infusion (62). However, when the inflammatory response became too pronounced (i.e., high IL-6 levels), antibiotics did not alter outcome (60). There is also evidence that antibiotics may increase endotoxin release from certain strains of bacteria, inducing a systemic inflammatory response syndrome (63). Unlike the beneficial effects of antibiotics, the clinical significance of this phenomenon in peritonitis remains unclear. In summary, mediators that activate leukocytes such as IL-12 play a central role in bacterial clearance in the abdominal cavity during secondary peritonitis. Antibiotics can improve outcome and inflammatory responses in peritonitis. Coagulation and fibrinolysis

The abdominal deposition of fibrin, the end product of activation of the coagulation cascade, is one of the macroscopic hallmarks of peritonitis. Endotoxin and inflammatory cytokines (IFN-+, granulocyte-macrophageYCSF) initiate coagulation by the expression of tissue factor (TF) on endothelial cells and activated leukocytes (primarily PM7) in the abdomen during peritonitis. This leads to fibrin formation (64Y66), which is normally cleared by the fibrinolysis system. Interferon + increased abdominal fibrin deposition, thus reducing bacterial movement through the abdomen and increasing entrapment of bacteria (67). In an E. coli peritonitis model, where fibrinolysis was impaired by tissuetype plasminogen activator (tPA) deficiency, bacterial load increased in the abdomen, liver, and lungs (68). The actions of the coagulatory system have both various beneficial and adverse effects in peritonitis. Fibrin clots localized the intra-abdominal infection by sequestering bacteria, thus inhibiting bacterial spread and preventing systemic sepsis, and consequentially reducing mortality (69, 70). However, when fibrin persisted and the patient failed to eradicate the encapsulated bacteria, abscesses were formed, which are associated with higher morbidity and mortality, mostly due to host defense failure (71). On the other hand, fibrin may also have a function in tissue repair and closing or restricting the intra-abdominal defect. Fibrin deposition in peritonitis results in the formation of peritoneal adhesions, which can cause various postsurgical complications such as intestinal obstruction, infertility, and chronic pain. Peritoneal adhesions thwart abdominal accessibility, hindering proper surgical source control during (re)laparotomy in the management of peritonitis. By far, the most severe complication of coagulopathy during peritonitis occurs when the inflammatory response is


SHOCK NOVEMBER 2007 no longer restricted to the peritoneal compartment, and systemic activation results in disseminated intravascular coagulation (DIC). The deregulation of coagulation can lead to microvascular thrombosis and MOF due to fibrin deposition, whereas on the other hand, it can also lead to increased hemorrhagic diathesis due to consumption of platelets and coagulation factors (72). Sepsis is the most common clinical condition associated with DIC (72), although the incidence of DIC in secondary peritonitis remains unknown. The pathogenesis of this coagulopathy is represented in Figure 1; coagulation is activated and fibrinolysis is inhibited. These responses occurred in abdominal exudate, blood, and lungs of peritonitis patients compared with controls (73, 74). In a rat peritonitis model, an increase of plasminogen activator inhibitor (PAI) 1 in the peritoneal fluid was a major cause for the reduction in fibrinolytic activity in the abdomen (75). Heat-killed microorganisms and cytokines such as TNF-!, IL-1", and transforming growth factor " induce PAI-1 production, resulting in a decrease of tPA in mesothelial cells (76, 77). Mesothelial cells are a major primary source of fibrinolysis inhibition, allowing for the deposition of fibrin throughout the peritoneum (76, 77). Indeed, in peritoneal biopsy homogenates of peritonitis patients, the net effect on fibrinolysis as measured by the PA activity (PAA) was significantly reduced compared with normal peritoneum (78). Patients undergoing elective surgery tend to have reduced peritoneal PAA (79). Peritonitis patients show substantially more reduced peritoneal PAA, with proportionately increased peritoneal levels of PAI-1 and PAI-2 (78). Notably, in the bronchoalveolar lavage fluid of peritonitis patients, PAA was reduced to 50% of normal values, whereas electively operated controls showed 100% PAA in bronchoalveolar lavage fluid (74). In summary, during peritonitis, coagulation is activated and fibrinolysis is inhibited both intra-and extra-abdominally. DISEASE SEVERITY AND MORTALITY This chapter investigates the role and dynamics of the various mediator systems during peritonitis in relation to disease severity and mortality.


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Prognostic factors in clinical peritonitis

It has been proven that disease severity expressed by both the occurrence and extent of organ failure determines the outcome of secondary peritonitis (80). There are only a few clinical studies that have examined inflammatory responses in human peritonitis. These studies have concentrated on the predictive value of cytokines in disease acuity, progression, and mortality. Plasma levels of C-reactive protein (CRP) were predictive of septic complications after elective surgery, as is soluble TNF-! receptor I (81), but neither was specifically predictive for peritonitis. The estimation of postoperative peritoneal cytokine levels (IL-6, TNF-!, IL-1") was a better indicative marker for peritoneal inflammation even before clinical manifestations develop (82, 83). However, the use of inflammatory mediators to assist in the diagnosis of peritonitis, which is often difficult, is still debatable. The diagnostic value of peritoneal cytokine levels is limited, and percutaneous puncture of fluid collections just to measure cytokines is potentially harmful and therefore not justified. Studies have shown that abdominal mediator levels do not indicate disease severity (30, 84, 85); instead, derangement of extra-abdominal inflammation indicates disease progression (86). The release of proinflammatory cytokines into the systemic circulation significantly correlated with the severity of peritonitis. Perioperative and postoperative plasma levels of TNF-! and IL-6 correlated with the Acute Physiology and Chronic Health Evaluation score (87, 88), which is a commonly used clinical score of disease severity (89). In addition, plasma levels of TNF-! have shown to be distinctive in predicting outcome in peritonitis patients (90). In peritonitis patients with septic complications, plasma concentrations of IL-8 were increased compared with noncomplicated patients, whereas abdominal chemotaxis did not differ (84, 91). Clinically severe peritonitis was associated with a stronger increase in oxygen radical generation and phagocytic capacity by PMNs in the circulation compared with the peritoneal cavity (92). Procalcitonin (PCT) is a plasma protein that only recently has been associated with the inflammatory response. Plasma levels predict adverse outcome of sepsis even better than IL-6 and CRP (93), and are also a good predictor of the development of septic complications in peritonitis patients (94). It

FIG. 1. The pathogenesis of (intra- and extra-abdominal) coagulopathy in peritonitis. Inhibition (dotted lines) and activation (straight lines) pathways in coagulation and fibrinolysis. Coagulation is activated and fibrinolysis is inhibited in various compartments due to increased generation of thrombin by endotoxin and inflammatory cytokines (IL-6 in particular) by enhancing TF expression and its complexing with activated factor VII (VIIa) (1); reduced inhibition of thrombin by inhibition of endogenous anticoagulant mediators (AT-III), TFPI, APC via TNF-! (2); and inhibition of fibrinolysis by activation of PAI-1 by inflammatory mediators (TNF-! in particular), inhibiting plasminogen activators (tissuetype and urokinase PA; tPA and uPA, respectively) (3). This reduces the disintegration of fibrin into fibrin degradation products (FDP).


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would be interesting to elucidate the pathophysiological role and function of PCT in inflammation and infection and, specifically, to better understand its role in the final step from sepsis toward mortality. In summary, in human peritonitis, increased plasma levels of cytokines and neutrophil activity indicate a priming of the systemic immune systems, and these are positively associated with increased disease severity. The prognostic and diagnostic values of abdominal mediator levels remain limited.

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TABLE 1. Kinetics of compartmental expression of mediators in peritonitis in relation to adverse outcome (severity/mortality) Protein

Compartment

Levels

Setting

Reference/s

Blood

,/j

Exp

86, 135, 161

Abdomen

j/=

Exp

86, 112, 135

Anti-inflammatory IL-10

Proinflammatory Blood

j

Exp

135

Abdomen

j

Exp

162

Blood

j

Clin

87, 88, 90, 163Y165

Mediator patterns in peritonitis severity and mortality

Blood

j

Exp

86, 166, 167

The kinetics of compartmental expression of mediators in peritonitis in relation to adverse outcome, defined as severe course or mortality, are shown in Table 1. The effect on mortality of various interventions, modulating mediator expression in experimental peritonitis, is shown in Table 2. Anti-inflammatory mediators—Anti-inflammatory cytokines can have both beneficial and adverse effects on mortality and disease severity. The beneficial survival effect of anti-inflammatory cytokines may be due to reduction of inflammatory tissue (and organ) damage (95Y97). As shown in Table 2, inhibition or genetic deletion of anti-inflammatory cytokines increases mortality in peritonitis models (23, 25, 95, 98). The supplementation of IL-10 therapeutically or IL-4 prophylactically protects against mortality (96, 97, 99, 100). Simultaneously, anti-inflammation may have an adverse effect because it can hamper bacterial clearance. Inactivation of IL-27, which is involved in the negative regulation of influx and oxidative burst in granulocytes, leads to a reduction in mortality (59). In summary, anti-inflammatory responses in peritonitis protect the host against overt inflammation, but could also play a role in conditional immunosuppression. Proinflammatory mediators—In peritonitis with adverse outcome, proinflammatory mediators are quite consistently increased in plasma (Table 1), but abdominal levels are not decisively increased or decreased. Levels of proinflammatory mediators in distant organs (lung) may also be increased. Prophylactic inhibition of early cytokines such as TNF-!, IL-1", and IFN-+ improved survival in certain peritonitis models (101Y103). However, these proteins were indispensable for the survival of peritonitis because genetic deletion of proinflammatory cytokines (TNF-!, IFN-+, IL-12, PLA2) led to increased mortality (Table 2) (13, 17, 47, 104, 105). However, therapeutic inhibition of IL-1" and TNF-! has not shown a significant impact on survival in human sepsis (106, 107). Thus, to improve survival, these cytokines must be prevented from early expression but must not be removed altogether. The application of G-CSF, which, like IL-12, is instrumental in stimulating (PMN) phagocytosis, decreased mortality when administered prophylactically and therapeutically (108, 109). Not surprisingly, inhibition of G-CSF with antibodies increased mortality (110). Unfortunately, there are no studies of G-CSF application in human peritonitis. Although IL-12 is important in bacterial clearance in the abdomen, it can have detrimental effects extra-abdominally, resulting in organ failure, most likely due to its activating effects on inflammatory cells. Activated cells are initially beneficial in the

Abdomen

j

Clin

90

Abdomen

=

Exp

86, 162, 166

Blood

j

Clin

87, 88, 90

Blood

135, 166

IL-1" IL-6

TNF-!

j/=

Exp

Abdomen

j

Clin

90

Abdomen

j/=

Exp

162

G-CSF

Blood

j

Exp

167

IFN-+

Blood

,

Exp

112

Abdomen

,

Exp

112

Lung

j

Exp

167

Blood

j

Exp

134

,/=

Exp

112, 134

IL-12

Abdomen IL-18

Blood

j

Clin

168

PCT

Blood

j

Clin

93, 94

CRP

Blood

j

Exp

43

C5b-9

Blood

j

Clin

117

Complement

Chemotaxis MIP-2 KC

IL-8 MCP-1

Blood

j

Exp

43, 169

Abdomen

j

Exp

169

Blood

j

Exp

43, 166

Lung

j

Exp

86, 166

Abdomen

=

Exp

86

Blood

j

Clin

30

Abdomen

=

Clin

30

Blood

j

Clin

129

Blood

j

Exp

167

Lung

j

Exp

167

Leukocytes O2 radicals Elastase

Blood

j

Clin

84

Abdomen

,

Clin

84

Blood

j

Clin

90

,/=

Clin

90 86, 134

Abdomen Lung

j

Exp

Abdomen

,

Exp

134

Blood

j

Clin

90

TAT

Blood

j

Exp

136

TM

Blood

j

Exp

136

Protein C

Blood

,

Exp

43

Blood

,

Clin

117

AT-III

Blood

,

Clin

117

Plasminogen

Blood

,

Clin

117

PAI-1

Blood

j

Clin

117

D-dimer

Blood

j

Clin

117

TFPI

Blood

j

Clin

74

TF

Lung

j

Clin

74

MPO Neopterin Coagulation

j/, = indicates levels of mediator are increased, decreased, or not influenced, respectively, in subjects with (subsequent) adverse outcome defined as more severe disease (shock, organ failure) or mortality; Clin, clinical (human) setting of study; Exp, experimental (animal model) setting of study; TAT, thrombin-antithrombin-III complex.


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TABLE 2. Experimental peritonitis studies: effects of specific immunomodulations on mortality Protein

Intervention

Route of administration

Treatment

Mortality

Reference/s

Anti-inflammatory IL-4

Administration

i.v.

Proph

,

170

IL-10

Genetic deletion

V

V

j

23

Inhibition

i.v.

Proph

j

95, 98

i.p./s.c.

Therap

,

96, 97, 99, 100

Proph

j

25

Administration IL-13

Inhibition

i.p.

IL-27

Genetic deletion

V

V

,

59

Inhibition

V

Therap

,

59

Proinflammatory V

V

j

17

i.p./i.v.

Proph + Therap

,

101, 159

Administration

i.p.

Proph

j

102, 111

Inhibition

i.v.

Proph

,

102, 103

Genetic deletion

V

V

j

104

IL-1RA

Administration

i.v.

Therap

,

171

IL-12

Genetic deletion

V

V

j

47, 105

Inhibition

i.v.

Proph

j

48, 49

Administration

i.p.

Proph + Therap

j

111

Administration

i.p.

Therap

,

112

G-CSF

Inhibition

i.v.

Proph

j

109

MIF

Inhibition

PLA2

Genetic deletion

HMGB-1

Inhibition

TNF-!

Genetic deletion Inhibition

IFN-+

Administration

i.v./s.c.

Proph

,

55, 108Y110

i.p.

Proph + Therap

,

113

V

V

j

13

i.p./i.v.

Therap

j

116

Complement IgM

Genetic deletion

V

V

j

120

C1q

Genetic deletion

V

V

j

57, 58

Factor B + C2

Genetic deletion

V

V

j

57, 58

C4

Genetic deletion

V

V

j

118

C3

Genetic deletion

V

V

j

56, 118, 119

C5a

Inhibition

i.p.

Therap

,

56

Chemotaxis KC

Inhibition

i.v.

Proph

j

32

MCP-1

Inhibition

i.p.

Proph

j

127

SCF (MCP-1)

Administration

i.p.

Proph

,

131

MDC

Inhibition

i.p.

Proph

j

126

Administration

i.p.

Therap

,

126

C-10

Inhibition

i.p.

Proph

j

128

Administration

i.p.

Therap

,

128

LTB-4

Genetic deletion

V

V

j

130

Oral

Proph

j

127

Genetic deletion

V

V

,

132

Inhibition CXCR-2 Adhesion CD-18

Inhibition

i.v.

Proph

,

40

E selectin

Genetic deletion

V

V

,

133

P selectin

Genetic deletion

V

V

,

133

Leukocytes NOS

Genetic deletion

V

V

j

105

Inhibition

s.c.

Proph

,

135

Inhibition

s.c.

Therap

j

135

Coagulation Protein C

Genetic deletion

V

V

j

172

APC

Administration

i.p.

Therap

,

142

TFPI

Administration

s.c./i.v./i.p.

Therap

,

143Y145

tPA

Genetic deletion

V

V

j

68

TF/VIIa

Inhibition

i.p.

Therap

=

149

AT III

Administration

i.p.

Therap

,

138

The effects of specific immunomodulatory interventions (administration [recombinant protein], inhibition [with monoclonal antibodies or receptor antagonists], or genetic deletion), influencing the expression of various inflammatory mediators, on mortality from experimental peritonitis. j/, indicates increase/decrease in mortality; MDC, macrophage-derived chemokine; Proph, prophylactic (intervention before induction of peritonitis); Therap, therapeutic (intervention after induction of peritonitis).


510


peritoneal cavity, but uncontrolled activation can eventually lead to cellular and tissue damage in remote organs (48). Kinetics of cytokine expression are crucial to peritonitis mortality. This was particularly exemplified by the neutralization of IL-12 with antibodies, which increased mortality (49) such as IL-12 pretreatment (111). On the other hand, delayed IL-12 administration during peritonitis improved survival (112). Another example of the time-dependent role of cytokines in peritonitis was demonstrated by macrophage migration inhibitory factor (MIF), a peptide that induces expression of proinflammatory mediators by PM7. Anti-MIF antibodies given up to 8 h after CLP protected normal mice and TNF-! knockout mice from death (113). Anti-MIF given 2 days after CLP with a subsequent superinfection increased mortality, whereas the administration of MIF during CLP and superinfection decreased mortality (114). High motility group box 1 (HMGB-1) was recently identified as a late mediator of systemic inflammation (115). Mortality decreased in CLP when HMGB-1 is inhibited up to 24 h after the induction of peritonitis (116). This also led to an increase in tissue repair (103). In summary, timing of intervention directed against proinflammatory mediators is important, and a balance between beneficial proinflammatory effects (infectious control) and adverse effects (systemic activation and tissue damage) needs to be found. Complement—Plasma levels of C5b-9, the end product of the complement pathway, were increased in nonsurviving peritonitis patients compared with survivors (117). In murine peritonitis models, mortality was increased to up to 100% when factors of the classical pathway (C1q, C2, C4), the alternative pathway (factor B), or the common pathway (C3) were deficient or inhibited (57, 58, 118, 119). Animals lacking natural IgM, a potent activator of complement, showed decreased inflammatory responses and decreased survival after CLP (120). In contrast, mortality was significantly reduced in CLP with mice lacking mannose binding lectin (MBL) A (121). Mannose binding lectin binds to glycoproteins expressed in the outer membrane of various microorganisms initiating complement activation via the lectin pathway. Mice have two functional forms of MBL, that is, MBL-A and MBL-C. In the above-mentioned experiment, MBL-C was not deficient (121). A lower overall concentration of MBL may have been favorable for the outcome of the peritonitis in this study, possibly due to a reduced proinflammatory reaction observed in blood and peritoneal cavity (121). If both forms of MBL had been absent, survival might have been less in the experimental mice than in wild-type animals because of increased susceptibility to infection. Notably, sepsis patients with MBL deficiency have increased morbidity and mortality (122). The blockade of C5a with anti-C5a antibodies prolonged survival (56). The proinflammatory nature of C5a in septic peritonitis is underlined by the fact that IL-6, a prominent proinflammatory cytokine correlating with survival in septic patients (123), has been shown to play a part in the increased expression of C5a-receptor in various organs after CLP in mice. Inhibition of IL-6 reduced the expression of C5aR and improved survival (124). In addition, when C3d binding is inhibited, tissue injury is reduced both locally and remotely (125).

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In summary, complement activation is instrumental in the eradication of intra-abdominal infection. However, inhibition of complement also reduces mortality, possibly due to reduced inflammatory tissue damage. A balanced, but not exaggerated, activation of the complement system is beneficial. Chemokines and adhesion molecules—Chemokine expression in blood is consistently increased in humans and animals with more severe peritonitis (Table 1). Abdominal kinetics of chemokines can vary, whereas chemokine levels (KC, MCP-1) increase in the lungs in disease progression. Intraperitoneal administration of chemokines reduced mortality and its inhibition increased mortality, as shown in Table 2 (32, 126Y128). However, high plasma levels of chemokines can be detrimental. In a recent study, 30 variables measured in blood were significantly different between survivors and nonsurvivors in a rat CLP model. From these 30 variables, high-plasma KC and MIP-2 were the best predictors of mortality (43). Early plasma levels of MCP-1 were higher in patients who subsequently died of peritonitis (129). Macrophage chemotactic protein 1 is essentially a CCchemokine, but it also indirectly attracts neutrophils via the production of LTB-4, a CXC-chemokine (127). Thus, increased mortality due to blockade of MCP-1 was probably an effect of reduced bacterial clearance due to the combination of reduced PM7 plus PMN phagocytosis (127). Direct inhibition of LTB-4 had the same effect on mortality (127). Genetic deletion of a LTB-4 receptor also increased mortality by reduced capacity of PMN migration and activation into the abdomen, whereas PMN activation increased in the blood and lungs (130). When mice were treated with the hematopoietic cytokine stem cell factor (SCF) before CLP, the survival rate improved, which can be attributed to SCF-stimulated release of MCP-1 (131). In the CLP model, i.p. administration of CCchemokines (macrophage-derived chemokine and C10) reduced mortality by stimulating abdominal host defenses, and a blockade had the opposite effect on survival of mice after CLP (126, 128). The inhibition of the CXC-chemokine KC increased early survival and reduced liver tissue damage after CLP (32). Furthermore, mice deficient in CXC-receptor 2 displayed reduced CLP-induced mortality and were thus protected from septic injury (132). Mortality due to detrimental effects of PMN activation leading to organ damage was reduced by inhibition of neutrophil adhesion. Inhibition of adhesion by CD18 antibodies reduced PMN infiltration in the lungs and alveolar damage, improving gas exchange (40), whereas genetic deletion of selectin genes improved kidney function (133). In summary, chemotaxis of leukocytes is warranted for peritonitis survival because the infection needs to be eradicated. Overexpression is detrimental, possibly due to extraabdominal PMN activation. Leukocyte factors—Overt leukocyte activation is a central component to adverse outcome in peritonitis. Elastase (PMN activation) and neopterin (M7 activation) plasma levels remained high in nonsurviving patients (90), whereas oxygen radical levels were higher in plasma in more severe peritonitis, as were MPO levels in the lungs (84, 86, 134). However, in the abdomen, levels were lower when severity


SHOCK NOVEMBER 2007 increased (84, 90, 134) (Table 1). This reflects a priming of the systemic and distant organ compartments in disease progression, whereas local defenses falter. Genetic deletion of NOS reduced mortality, probably by reducing tissue damage (105). Prophylactic partial inhibition with low doses of a NOS antagonist had the same effect. When the dose was increased mildly, the survival rate increased even further. When high doses of a NOS antagonist were applied, the survival rate fell to 0% in 2 days after CLP, just like post-CLP NOS inhibition (135). In summary, leukocyte activation is increased extraabdominally in subjects with adverse outcome. Coagulation and fibrinolysis—In a primate model of peritonitis, plasma levels of thrombin-antithrombin