THE PATHOGENESIS OF SEPSIS

~~

~

~

0272-5231/96 $0.00

THE SEPSIS SYNDROME

+

.20

THE PATHOGENESIS OF SEPSIS Factors That Modulate the Response to Gram-Negative Bacterial Infection Clay B. Marsh, MD, and Mark D. Wewers, MD

The sepsis syndrome is defined as “the systemic response to infection.”26,38 Intrinsic to this definition is the central role of infection as an inducer of the host immune response. The sepsis syndrome is the 13th leading cause of mortality in the United States, accounting for an estimated 100,000 deaths per year.%* Despite recent advances in medical technology, the average mortality of the sepsis syndrome remains approximately 40%, and its la incidence is in~reasing.~~, For the host to defend against invading gram-negative bacteria successfully, a coordinated cascade of inflammatory mediators is released by immune leukocytes=, 26, 132 and tissue parenchymal cells.171This article focuses on the important components of this cascade, which help determine the host’s response to gram-negative bacterial infections. INITIATORS OF THE SEPSIS SYNDROME

Gram-negative Bacteria

d r ~ m e .30,~46~In , healthy subjects, gram-negative bacteria reside primarily in the gut, where intact barriers prevent translocation into the host’s bloodstream.26,51, 160, 186, 191 In disease states, however, several factors can lead to bacterial translocation, including (1) alteration in the host flora, resulting in bacterial overgrowth; (2) host immune dysfunction; and (3) increased permeability across epithelial cell barrier^.^, 73, x7, 160, 19* Experimental data suggest that dysfunction of the reticuloendothelial system (primarily the liver) during sepsis is another important factor in bacterial translocation to the blood~tream.~~ Once the gram-negative bacteria gain access to the bloodstream, lipopolysaccharide (LPS), a bacterial cell wall moiety, interacts directly with leukocytes and parenchymal cells to induce an inflammatory cascade.90,124* 132, 139, 141, 171 In this manner, translocation of gramnegative bacteria to the bloodstream is an important early event in the pathogenesis of gram-negative sepsis.

Blood-borne infections with gram-negative bacteria are a leading cause of the sepsis syn-

Lipopolysaccharide

This article is supported by grants No. HL40871, HL.53229, American Lung Association of Ohio, Francis Families Foundation.

LPS is an integral cell wall component of gram-negative bacteria necessary for bacterial survival.154The critical components of LPS

From the Departments of Internal Medicine (CBM) and Medicine (MDW), Division of Pulmonary and Critical Care Medicine, Ohio State University College of Medicine, Columbus, Ohio ~

CLINICS IN CHEST MEDICINE VOLUME 17 * NUMBER 2 * IUNE 1996

183

184

MARSH & WEWERS

necessary for the growth of gram-negative bacteria are the lipid A moiety and two 3deoxy-D-manno-octulosonic acid residues.154 After antibiotic agents or host immune modulators lyse the bacteria, LPS becomes more accessible to the host's circulation and induces target cells, including monocytes and macrophages, to release inflammatory mediators that initiate the immunologic cascade.59 To initiate this cascade, LPS's lipid A moiety binds to CD14, a glycosylphosphoinositol 114, (Gpi)-linked receptor on host le~kocytes.~~, 153,166,199 LPS's role as an important inducer of the sepsis syndrome and initiator of the cytokine cascade is evidenced by the reproduction of these clinical states with intravenous LPS injections into humans or animals.4,8,Z.l. 56, 124, 126, 178 Lipopolysaccharide-CD 14 Interaction

LPS interacts with target cells through binding to CD14, a 55-kd Gpi-anchored receptor found mainly on mononuclear phagocytes.66,96, lW Two soluble forms of CD1462 that retain binding affinity to LPS can induce the host's inflammatory cascade and the sepsis syndrome.8,88, 163 Interestingly, many investigators realized that serum augmented LPS's target cell effects.lu The source of the augmentation was a 60-kd serum protein, termed lipopolysaccharide-binding protein (LBP).165,lal LBP is produced primarily by the liver and binds to and opsonizes the lipid A moiety of LPS, catalyzing the binding of LPS to CD14.165 LBP first was identified as an acute-phase response protein,181,la2but recent studies suggest that constitutive levels of LBP found in normal serum are sufficient to catalyze the interaction of LPS and CD14.'02 LBP-LPS complexes interact with the soluble or Gpilinked CD14 to promote LPS's target cell eff e c t ~In . ~addition ~~ to LBP, additional serum factors with protease activity, termed septin, can accelerate the interaction of LPS and CD14.198Septin activity resembles a similar activity found in horseshoe crabs that avidly binds to the lipid A moiety of LPS.198Interestingly, septin-like proteins from the horseshoe crab form the basis for the limulus amoebocyte lysate assay, which binds and detects LPS.194The role of septin in the physiology of sepsis is still to be determined. Whereas LPS induces the host to unleash a coordinated inflammatory response, uncontrolled activation of inflammatory cells like polymorphonuclear leukocytes (PMNs) can

result in injury or death of the host. To reduce the burden of invading gram-negative bacteria, therefore, the azurophilic granules of PMNs contain the 55-kd bactericidal/permeability-increasing protein (BPI),IMwhich is cytotoxic to gram-negative bacteria.195Of note, BPI has a striking DNA sequence homology to LBP and similarly binds the lipid A moiety of LPS.82,197 In contrast to the catalytic activity of LBP, however, BPI competitively inhibits LPSCD14 interaction.s2,119 Animal studies show that BPI inhibits LPS's in vivo target cell effects.70In addition, other serum factors, including lipoproteins, can bind LPS to reduce the inflammatory cascade.200 As evidence for CD14's critical role in determining host responses to LPS, transgenic animals overexpressing CD14 show enhanced sensitivity to LPS-induced septic Because CD14 exists as a soluble or Pi-linked receptor lacking a cytoplasmic signaling domain, most investigators suspect there are other signal-transducing receptors for CD14 or the CD14-LPS complex.88,163 An 80-kd receptor recently was identified on a monocyte cell line that preferentially binds LPS in the presence of LBP.150,163 Whether this receptor is an LPS-signaling receptor remains to be determined. The interaction between LPS and its receptor, CD14, is promoted and inhibited by serum factors that determine the ultimate host immune response to endotoxemia. These concepts are represented schematically in Figure 1. IMMUNOLOGIC MEDIATORS OF THE LIPOPOLYSACCHARIDE-INDUCED SEPSIS SYNDROME

A large volume of experimental work shows that LPS modulates its pathologic effects through the induction of second messenlZ6,139, 147 Perhaps gers, including cytokine~.~~, the best evidence for this relationship is the failure of anti-LPS antibodies to interrupt the sepsis cascade, unless these antibodies are infused before bacterial infection.203The two early-response cytokines that are important in modulating the inflammatory cascade induced by LPS are tumor necrosis factor-a (TNF-a) and interleukin-1p (IL-1p).", 132 These cytokines stimulate immune responses, in57, 85, lZ3,171 arachicluding cytokine donic acid metabolism,173 integrin expression,6O complement activation,162and nitric oxide p r o d ~ c t i o n .190 ~~,

-

THE PATHOGENESIS OF SEPSIS

185

liver

Gram. negative bacteria

- II LPS removal

<

signal transdu ction

4i

cytakine release Figure 1. Endotoxin-signalingevents. The key events in the response of macrophage to endotoxin (LPS) are shown schematically. The cell walls of gram-negative bacteria display an integral component of the cell wall, termed lipopolysaccharide (LPS), that is released from the bacteria during bacterial lysis by phagocytes or antibiotic lysis. LPS is opsonized by binding to the hepatocyte acute phase protein (LBP). LBP binding catalyzes the interaction of LPS with the endotoxin receptor CD14. CD14 is a phosphatidylinositol-linked receptor that does not have a known signaling sequence. Current concepts are that the LPS/LBP/CDl4 complex then interacts with a putative signaling receptor that provides the signal transduction. Other molecules may shunt the LPS away from this signaling complex. For example, BPI has high affinity for LPS but does not allow it to interact with CD14. Additional factors (not shown) include scavenger receptors that may clear LPS without signaling.

Cytokine Induction Tumor Necrosis FactorTNF-a is produced primarily by mononuclear phagocytes in response to LPS2,5, 132 or other ~ y t o k i n e sas ~ ~a membrane-bound 26kd pro-TNF-e~,’~~ which is cleaved by a metalloprotease to yield the mature 17-kd soluble 183 Interestingly, TNF-a biologic activity requires three 17-kd TNF-a monomers to form a homotrimeric complex, which then

can bind and cross-link p55 (55-kd) type I or p75 (75-kd) type I1 TNF receptors (TNFR).14 The type I TNFR apparently modulates much of TNF-a’s LPS-induced activity, whereas the type 11 TNFR is important in TNF-alS2 Monocytes mediated cellular cytotoxicity.22, and macrophages are the central source of TNF-a protein, but TNF-a also is produced by brain glial cells, liver Kupffer’s cells, skin keratinocytes, mast cells, NK-lymphocytes, T lymphocytes, and B lymphocytes.183

186

MARSH & WEWERS

Although serum TNF-a levels have been associated with sepsis and its outcome, it has not been shown whether TNF-a functions locally or systemically to induce the sepsis syndrome. In vivo administration of LPS induces a burst of serum TNF at 90 minutes that is undetectable by 4 hours.lZ9Intravenous TNF infusions produce a clinical picture that resembles early sepsis, with a dramatic drop in blood pressure and leukopenia followed by l e ~ k o c y t o s i s(Fig. ~ ~ ~ 2). Because TNF-a has many downstream effects in the inflammatory response, chronically elevated serum TNF-a levels may not be necessary to produce the sepsis syndrome. Experimental evidence shows clearly that TNF-a is a key mediator in the LPS-induced sepsis syndrome.21,78, ls4, lS5 Transgenic p55 type I TNFR "knock-out" mice, for example, do not display hernodynamic or systemic immune alterations to intravenous LPS, whereas control animals develop symptoms sugges-

pre

30 min

4 h

24 h

Time after TNF Infusion

Figure 2. Effect of TNF infusion in humans. TNF infusions in humans have profound effects. Shown here is the effect of a 30-minute infusion of TNF-IX on the plasma mononuclear cell population (m), neutrophil population ( 0 ) and blood pressure (systolic [filed bars] and diastolic [hatched bars]) in five patients being treated for malignancy. Although circulating TNF-IX levels were gone by 4 hours (data not shown), this was the time of maximum hypotension and depression of mononuclear cells. Patients also experienced chills and low-grade fever at the 4-hour time point (data not shown). (Adapted from Wewers MD, Rinehart JJ, She 2-W, et al: Tumor necrosis factor infusions in humans prime neutrophils for hypochlorous acid production. Am J Physiol Lung Cell Mol Physiol 259:L276-L282, 1990; with permission.)

tive of the sepsis In contrast, transgenic type I1 TNFRp75 "knock-out" mice show a marked reduction in TNF-ainduced tissue destruction but do not show LPS r e ~ i s t a n c eThese . ~ ~ data substantiate the critical role of TNF-a in LPS-mediated sepsis and the differences in signal transduction between the type I and I1 TNFRs in response to LPS stimulation. In addition to the transgenic experiments, other animal models show conclusively that intravenously administered rTNF-a mimics LPS-induced sepsislS4 and soluble recombinant p55 TNFRs or anti-TNFa neutralizing antibodies block symptoms and hemodynamic problems suggestive of the LPS-induced sepsis syndrome.21,131, lS5 Although experimental data show that uncontrolled TNF-a production may lead to the sepsis syndrome, there also are data to suggest that TNF-a plays a critical role in host defense to invading bacteria.138* 152 Complete TNF-a blockade may have deleterious effects because intravenous bacteria result in high mortality in transgenic TNFR type I-deficient mice and mice treated with neutralizing antiTNF-ol antibodies versus controls.138,152 In these mice, the cause of death is overwhelming infection attributable to the inability to clear the bacterial 10ad.l~~ Phase I1 data from human sepsis trials using recombinant soluble TNFRs (rsTNFR) show that subgroup mortality in patients receiving high concentrations of the rsTNFR is higher than that in a conventionally treated placebo gr0up.l In aggregate, these data suggest that a TNF-a response,to invading bacteria is essential for host integrity, but that overabundant secretion of TNF-a can lead to host injury and death. Tumor Necrosis Factor-a 's Effects on the Inflammatory Cascade

TNF-a induces LPS-mediated sepsis through the induction of the cytokine cascade.183In this manner, TNF-a displays pleiotropic effects on inflammatory and parenchymal cells. TNF-a induces the production of the other early-response cytokine, IL-157, chemotactic cytokines, including IL-8,'71 a powerful neutrophil chemoattractant; IL-6,78which induces acute-phase response proteins; nitric oxide (NO),136a primary inducer of sepsis-associated hypotension, pulmonary hypertension,"jl and the putative myocardial depressant factor of sepsis113, arachidonic m e t a b ~ l i s m ~ ~ ; and m i c r o t h r ~ m b i In . ~ ~addition ~ to these in-

THE PATHOGENESIS OF SEPSIS

direct effects on the host, TNF-a is an endoge-

nous pyrogen that can induce fever and is responsible for the catabolic state seen in sep57 Imsis through its effects as ”cachexin.”zO, portantly, mortality from sepsis is correlated directly with serum TNF-a levels,”8 providing more evidence that this early-response cytokine plays a critical role in determining the host outcome from bacterial infection.

Interleukin-l p

IL-1 shares many functional and biologic characteristics with TNF-a. (Figure 3 provides an overview of IL-1 and TNF overlap.) Structurally, the IL-1 family consists of three genes located on chromosome 2 that encode distinct proteins-11-la, IL-lp, and IL-1 receptor antagonist (IL-lra).%IL-1p and IL-la are able to induce a sepsis-like syndrome when administered intravenou~ly.~~, IL-1p is produced as a predominantly intracellular 31-kd pro-ILl p that lacks a classic leader signal peptide sequence.12,97 Pro-IL-lp is processed by the

cysteine protease, IL-1 converting enzyme (ICE), to the biologically active 17-kd mature Because IL-1p does not go IL-lp.23,z4, 39, through the Golgi secretory pathway, the mechanism by which processed, biologically active 17-kd is secreted from the cell is unknown. Once secreted, 17-kd IL-1p binds to the 80-kd type I signaling IL-1 receptor (IL1R) to induce its biologic effects.17zIn contrast, the 68-kd type I1 glycosylphosphoinositollinked IL-1R serves as a decoy receptor, competitively binding 17-kd IL-1p and inhibiting IL-1p’s target cell effects.z9,*,86 Interestingly, the shed type I1 IL-1R works synergistically with IL-lra in blocking IL-1p’s target cell eff e c t ~Of . ~note, ~ the release of type I1 IL-1R is regulated by IL-4 and glucocorticoids, which may serve as a physiologic feedback mechanism to regulate the LPS-driven inflammatory response.4z,86 Experimental data suggest that I t - l p also is a critical determinant of host outcome in animal and human models of sepsis.4,47, 76, Iz8, 146 Transgenic ”knock-out” mice lacking

Endo thelium

Neutrophil

NO release

oxidants

ICAM-1

chemotaxis

E selectin

adherence to endo thelium

permeability

I u

[Macrophage IL-l/

~~~

Liver 0

acute phase response

~~

Fibroblast

I

Brain

0

lL-8 collagenase

- LBP - C reactive protein

fever

proliferation

anorexia sleep 0

187

corrisol

Figure 3. Overview of TNF and IL-1 functions in sepsis. Representative examples of the functions of these early response cytokines on neutrophils, fibroblasts, brain, liver, and endothelium. Note the near complete overlap save for acute phase protein production in which TNF is replaced by IL-6.

188

MARSH & WEWERS

ICE are resistant to LPS’s effects,”’ suggesting that the generation of mature 17-kd IL-lp is critical to the expression of the sepsis syndrome. In addition, experiments in animal and human subjects show that competitive inhibition of 17-kd IL-1p’s binding to the type I IL-1R by IL-lra reduces systemic symptoms and morbidity and mortality in response to intravenous administration of LPS or bacteFinally, soluble type I1 IL-1 decoy ria.4,76, receptors reduce LPS-mediated target cell effects.“, 86 Despite plentiful experimental data to suggest the important role of IL-1p in sepsis, however, a human phase I1 trial of ILIra in sepsis did not show an overall survival benefit.” These data suggest that interruption of an early component of the cytokine cascade is insufficient to block the inflammatory response once the cascade has been initiated. Whether the lack of effect is attributable to innate redundancy in this inflammatory cascade or whether it reflects the futility of affecting early mediators once the cascade has been stimulated is unclear. From the alternative perspective, tight control of IL-1p concentrations may be critically important-i.e., a sufficient concentration is needed for host defense but high levels may lead to tissue injury. This is best illustrated in an animal model of Klebsiella sepsis, in which moderate amounts of exogenous IL-lra reduce mortality, but increasing amounts of IL-lra increase the mortality rate because animals are unable to kill the invading bacteria.’l5 Taken together, these data suggest that IL-1p has an important, but not independent role in the generation of the sepsis syndrome and that, concurrently, a critical functional level of IL-1p is necessary for host defense. lnterleukin-lp’s Effects on the hflarnrnatory Cascade

Similar to TNF-a, IL-lp is a powerful inducer of secondary mediators of the sepsis syndrome. IL-16 is a powerful inducer of a cadre of inflammatory cytokines, including TNF-a and IL-l,85,91, 123 which act synergistically to augment the inflammatory cascade; chemokines, including 1L-8157, 171 and monocyte chemoattractant pr0tein-1,’~~ which are powerful neutrophil and monocyte chemoattractants; IL-2,% inducing T-lymphocyte proliferation; IL-6,65 which stimulates acutephase response proteins; the colony stimulating factors56,loo; and the clotting cascade.90In addition, secreted IL-lp stimulates the pro-

duction of factors that suppress further IL-lP production--e.g., IL-lra18,120 and IL-454-and factors that suppress the type I IL-1R expresIn addition to its effects sion on target on cytokines, IL-1p activates other important mediators of the sepsis syndrome, including arachidonic acid metabolites68 and integrin expression on leukocytes and parenchymal 136, Furcells,54as well as generating thermore, IL-1 p directly induces fever, sleep, anorexia, and neuropeptide release.54 IL-1 p therefore exists in delicate balance between being a defender of host integrity and an initiator of the sepsis syndrome. Other Cytokines

Interleukin-1 Receptor Antagonist

IL-lra is a 21 to 23 kd protein member of the IL-1 family.%,64 Mutational analyses suggest that IL-la, IL-lp, and IL-lra diverged IL-lra is a pure competifrom a single tive antagonist of IL-1p’s binding to the signaling type I IL-lR, blocking IL-1p’s target cell effects.l0. 94, 127 Because only 1% to 10% of the type I IL-1R need to be engaged by IL1p to promote signal transduction, however, IL-lra must be in 50 to 100 fold excess to IL-1p to be effe~tive.~ Experimental models support this observation because IL-lra can suppress LPS-induced or IL-1-induced IL-1p, IL-la, and TNF-a release from mononuclear 93, 121 In addition, peripheral phagocyte~.~~, blood mononuclear cell IL-ra is stimulated by IL-1p and TNF-a, which provides an endogenous feedback loop to suppress inflammatory cytokine production.120In animal models, ILIra reduces mortality from intravenous LPS 76, 146, 193 In addition, and bacterial infu~ion.~, normal human volunteers receiving intravenous LPS have approximately 100-fold higher levels of IL-lra than IL-1p in their suggesting IL-1p regulation is important to host homeostasis. This concept is shown by primate sepsis studies in which serum IL1p levels predict mortality, whereas survivors and nonsurvivors have similar serum IL-lra concentrations.n Taken in aggregate, these data suggest that regulation of IL-1p is an important determinant of host outcome in bacterial sepsis. Interleukin-6

IL-6 is a 26-kd protein produced by monocytes, macrophages, lymphocytes, and fibro-

THE PATHOGENESIS OF SEPSIS

IL-6 has pleiotropic effects, including the stimulation of B-cell immunoglobulin production, T-cell proliferation, natural killer cell activation and cytotoxicity,28and acutephase protein secretion by the liver.37Experimental studies in animals and humans show that IL-6 is released reproducibly 4 to 6 hours after LPS or live bacterial challenge and dissiMany pates during the next 24 to 48 studies directly correlate serum IL-6 with morbidity and mortality in patients with septic ~hock,3~, 192 but a direct link between IL-6 release and LPS-induced mortality is difficult to find. For instance, transgenic IL-6 ”knockout” animals produce three times the amount of TNF-a in response to an intravenous LPS challenge produced by control mice but have no difference in mortality from 112 In contrast, IL-6 ’%nock-out” mice fail to control vaccinia virus and Listeria rnonocytogenes infections.lmThese data suggest that although IL-6 may be a key determinant in outcome from certain infections, it does not appear to predict host survival from bacterial LPS. IL&induced acute-phase proteins, however, differ in mice (predominantly serum amyloid A) and humans (predominantly C-reactive protein). IL-6 “knock-out” experiments therefore have to be interpreted with caution. Interieukin-10

IL-10 is a suppressive cytokine produced by a variety of cells, including monocytes and macrophages, T lymphocytes, B cells, neutrophils, and mesangial cells.79,89* Experimental evidence suggests that IL-10 plays a critical role in protecting the host from organ injury and death in gram-negative sepsis.36,117 Many studies show that animals receiving intravenous or intraperitoneal IL-10 are protected from LPS-induced mortality.83, lo4, 158 IL-10 apparently exerts its protective activities through inhibition of inflammatory mediators-TNF-a and IL-1p,36,83, 116 IL-8,36interferon-y,l16 NO,@ IL-6,98 and prostaglandin metabolites.143Human phase I trials of IL-10 show a significant dose-dependent (65%95%) inhibition of TNF-a and IL-1p production from whole blood stimulated ex vivo from patients in the trial.41In contrast, serum IL-10 levels are correlated with mortality in patients with meningococcal disease.52Taken together, these data suggest that IL-10 functions as an important regulator of the immune response.

189

Interleukin-8

IL-8 is the best known member of the C-XC chemokine family, which, as a group, are primarily chemotactic for neutrophils and, to a lesser degree, for 1ymph0cytes.l~The C-X-C chemokine family gains neutrophil chemotactic properties from an N-terminal ELR (glutamine-leucine-arginine) motif.13 IL-8 is produced by a variety of cells, including monocytes, macrophages, lymphocytes, neutrophils, endothelial cells, fibroblasts, and epithelial cells, in response to LPS, IL-1, or TNF stimulation.13,lZ4*171 IL-8 apparently is an important determinant of neutrophil recruitment to an inflammatory focus.3,13, 133 Transgenic mice overexpressing IL-8 have altered ability to recruit neutrophils to an inflamed compartment because of downregulation of neutrophil L-~electin,’~~ suggesting that targeted deposition of IL-8 is necessary for a neutrophil response to compartmentalized bacterial infection. In humans, the Duffy blood group antigen on red blood cells can bind and neutralize systemic IL-8, which may serve to limit systemic effects of IL-8.4sStudies of septic patients show that high serum IL-8 concentrations portend higher mortality and incidence of multiple organ dysfuncti011.l~~Regulated deposition of IL-8 therefore is important in targeting the immune response. Interferon-y

Interferon-? (IFN-y) is a 40 to 70 kd glycoprotein product of activated T lymphocytes with pleiotropic effects on macrophages, monocytes, fibroblasts, endothelial cells, and epithelial ~ e 1 l s . lInterferon-y-activated ~~ cells are important defenders against a variety of pathogens, including gram-negative and gram-positive bacteria.135Mice subjected to lethal LPS concentrations are protected by neutralizing anti-IFN-y antibodies.101,lo7 Similarly, subcutaneous IFN-y injections following cecal ligation and puncture result in a dose-dependent increase in death, compared with vehicle-injected Similarly, transgenic IFN-y receptor ”knock-out” (IFNy R -/-) mice survive LPS doses 100 to 1000 times the minimum lethal dose of wild type In addition, the IFN-y R -/- mice produce 10-fold less serum TNF-a than controls but have similar TNFR expre~sion.~~ Taken together, these data suggest that IFNy has an important role in determining host

190

MARSH & WEWERS

outcome of gram-negative sepsis, potentially via stimulation of TNF-a release.

Miscellaneous Factors Nitric Oxide

Arachidonic Acid Metabolites

NO is a low-molecular-weight, membranepermeable gas that functions as a regulator of Prostaglandin metabolites play an imvascular tonela and an inhibitor of platelet portant role in the pathogenesis of sepsis and aggregation and leukocyte a d h e ~ i 0 n . There l~~ the sepsis syndrome. Because this topic is are two forms of N k o n s t i t u t i v e NO that covered in detail elsewhere in this issue, this is produced by a calcium-dependent NO synsection is limited to two important arachithase and inducible NO (iNO) that is induced donic acid metabolites in the sepsis synby inflammatory mediators such as IL-lp16 drome-platelet-activating factor (PAF) and and TNF-aI6,lWand is produced by a calciumleukotriene-B, (LTB,). independent NO synthase.’40 The i N 0 produced by vascular smooth muscle cells and Platelet-activatingFactor endothelial cells in sepsis largely accounts for 113 given that NO LPS-induced hypoten~ion,6~, PAF is a phosphoglyceride secreted by a inhibitors can reverse hypotension in septic variety of cells, including monocytes, mesananimals.69, lo3 NO synthase inhibition seems gial cells, and endothelial cells, in response to to be a two-edged sword, however, because LPS.31 Among PAF’s target cell effects are several studies show detrimental effects from stimulation of TNF-a,’” IL-1P,l5 inducible NO synthase inhibition in sepsis, including NO,176tissue factor,lo6 leukocyte adherence reduction in organ blood flow and an inand activation,” platelet aggregati~n,”’~ pulcreased incidence of multiple organ dysfuncmonary hypertension,40and a shock-like state in response to intravenous admini~trati0n.l~~tion syndrome.81,la0 In addition, in vitro studies suggest that NO may be the myocardial Animal studies show that PAF receptor andepression factor of sepsis.’87Interestingly, a tagonists reduce the incidence of LPShuman sepsis trial shows that NO synthase induced and live bacteria-induced death, pulinhibition increases peripheral vascular resismonary hypertension, and disseminated tance and blood pressure, at the same time intravascular coagulation in a dose-depenreducing cardiac output, suggesting that NO dent manner.’06In addition, a phase I human has pleiotropic physiologic effects.I5’ trial using a PAF receptor antagonist in gramnegative sepsis showed a survival benefit for treated patients.53PAF therefore plays an important role in the etiology of hypotension, Complement leukocyte activation, and mortality from bacThe complement cascade consists of a terial sepsis. group of related proteins that act in an orchestrated, sequential manner to opsonize Leukotriene B, and destroy targets of phagocytic cells and LTB, is a dihydroxy acid derivative of arapromote their removal.80 The complement chidonic a ~ i d . 9LTB, ~ produced in response system has two major pathways-(1) the clasto invading bacterial pathogens has activities sical pathway, which is activated by antiimportant for neutrophils, including chemobody-coated targets or antigen-antibody taxis and acti~ati0n.I~~ As evidence for this complexes and (2) an alternate pathway, concept, an LTB, receptor antagonist reduces which is activated by targets in the absence LPS-mediated hypotension and pulmonary of antibodies.80The importance of the complearterial hypertension and increases in pulmoment system in host defense against bacterial nary vascular interstitial water, suggesting infections is evidenced by recurrent encapsuLTB, may have other important immunologic lated bacterial infections in patients with tereffects.145In patients with sepsis, high-circuminal complement deficiencies.lloIn addition, lating concentrations of LTB, correlate with primates given lethal doses of gram-negative death, cytokine secretion, and vascular endobacteria increase activated complement levels LTB, therefore is anthelial dy~function.’~~ 5 to 13 fold baseline values, whereas surviother important member of the inflammatory vors increase complement levels only 2 to cascade in gram-negative infections. 3 times.%

THE PATHOGENESIS OF SEPSIS

lntegrins and Adhesion Molecules

Integrins are a family of cell surface proteins that mediate cell adhesion'" to target the host inflammatory response. After LPS challenge, endothelial cells express several adhesion molecules, including intracellular adhesion molecule-1 (ICAM-l), which bind to neutrophil MAC-1 (CDllb/CD18) and target neutrophils to the inflamed compartment.58,159 These neutrophils are necessary to fight the invading pathogens but also may modulate tissue injury. The latter point is underscored by studies blocking CD11/CD18b ligands, which attenuates LPS-induced tissue injury.71,169 In addition, ICAM-l-deficient transgenic mice are resistant to the lethal effects of high doses of LPS, suggesting this pathway is critical in promoting systemic effects of gram-negative bacterial sepsis.201 fcr Receptors Fcy receptors (FcyRs) are leukocyte membrane receptors that modulate the removal of immunoglobulin G-opsonized Engagement of monocyte FcyRs concomitant with gram-positive or gram-negative bacteria increases the sensitivity for LPS-induced ILl p release by 1000-fold while suppressing IL-lra,", which favors a proinflammatory environment. In addition, IgG-containing immune complexes, as may be seen with opsonized bacterial particles, use FcyRs to induce an immune response. As evidence for this concept, transgenic mice lacking critical FcyR-mediated signal transducing elements are unable to recruit neutrophils in response to deposition of immune complexes.*75The authors found that FcyR cross-linking is a powerful stimulus for monocyte IL-8.122The failure to recruit neutrophils in the transgenic animals therefore probably relates to lack of IL-8 production. In summary, this article reviews important host immune mediators in response to bacterial sepsis. The determinant of host outcome lies in the regulation of these proteins. Tightly regulated expression of these mediators is critical for normal homeostasis and host defense, whereas overexpression can result in tissue injury, multiple organ dysfunction syndrome, and death.

References 1. Abraham E, Wunderink R, Silverman H, et al: Efficacy and safety of monoclonal antibody to tumor

191

necrosis factor-a in patients with sepsis syndrome. JAMA 273:934-941, 1995 2. Agganval BB, Kohr WJ, Hass PE, et al: Human tumor necrosis factor: Production, purification, and characterization. J Biol Chem 260:2345-2354, 1985 3. Akahoshi T, Endo H, Kondo H, et al: Essential involvement of interleukin-8 in neutrophil recruitment in rabbits with acute experimental arthritis induced by lipopolysaccharide and interleukin-1. Lymphokine Cytokine Res 13113-116, 1994 4. Alexander HR, Doherty GM, Buresh CM, et al: A recombinant human receptor antagonist to interleukin 1 improves survival after lethal endotoxemia in mice. J Exp Med 173:1029-1032, 1991 5. Allen JN, Herzyk DJ, Allen ED, et a 1 Human whole blood interleukin-lp production: Kinetics, cell source, and comparison to TNF-a. J Lab Clin Med 119:538-546, 1992 6. Anderson CL, Shen L, Eicher DM, et al: Phagocytosis mediated by three distinct Fcy receptor classes on human leukocytes. J Exp Med 171:1333-1345, 1990 7. Andriole V T Urinary tract infections in the 90s: Pathogenesis and management. Infection 2O(suppl 4):5251-S256, 1992 8. Arditi M, Zhou J, Dorio R, et al: Endotoxin-mediated endothelial cell injury and activation: Role of soluble CD14. Infect I m u n 61:3149-3156, 1993 9. Arend WP: Interleukin 1receptor antagonist: A new member of the interleukin 1 family. J Clin Invest 88:1445-1451, 1991 10. Arend WP, Joslin FG, Thompson RC, et a1 An IL-1 inhibitor from human monocytes: Production and characterization of biologic properties. J Immunol 143~1851-1858,1989 11. Arend WP, Smith MF, Janson RW, et al: IL-1 receptor antagonist and IL-1 p production in human monocytes are regulated differently. J Immunol 1471530-1536,1991 12. Auron PE, Warner SJC, Webb AC, et al: Studies on the molecular nature of human interleukin 1. J IIIUINWIO~ 138:1447-1456, 1987 13. Baggiolini M, Dewald B, Moser B Interleukin-8 and related chemotactic cytokines-CXC and CC chemokines. Adv Imunol55:97-179, 1994 14. Banner DW, DArcy A, Janes W, et al: Crystal structure of the soluble human 55 kDTNF receptorhuman TNF-p complex: Implications for TNF receptor activation. Cell 73:431-445, 1993 15. Barthelson RA, Valone F H Platelet-activating factor stimulates expression of IL-1p mRNA in THP-1 cells. Lipids 26:257-260, 1991 16. Beasley D, Eldridge M: Interleukin-lp and tumor necrosis factor-n synergistically induce NO synthase in rat vascular smooth muscle cells. Am J Physiol 266(pt 2):R1197-R1203, 1994 17. Bendtzen K, Mandrup-Poulsen T, Nerup J, et al: Cytotoxicity of human p l 7 interleukin-1 for pancreatic islets of Langerhans. Science 1545-1547, 1986 18. Berger AE, Carter DB, Hankey So, et a1 Cytokine regulation of the interleukin-1 receptor antagonist protein in U937 cells. Eur J Immunol233945,1993 19. Beutler B, Cerami A: Cachectin and tumor necrosis factor as two sides of the same biological coin. Nature 320:584-588, 1986 20. Beutler B, Cerami A: Cachectin: More than a tumor necrosis factor. N Engl J Med 316:379-385, 1987 21. Beutler B, Milsark IW,Cerami AC: Passive immunization against cachectin/tumor necrosis factor pro-

192

MARSH&WEWERS

tects mice from lethal effect of endotoxin. Science 229869471, 1985 22. Bigda J, Beletsky I, Brakebusch C, et al: Dual role of the p75 tumor necrosis factor (TNF) receptor in TNF cytotoxicity. J Exp Med 180445-460,1994 23. Black RA, Kronheim SR, Sleath PR Activation of interleukin-lp by a co-induced protease. FEBS Lett 247386-390, 1989 24. Black RA, Kronheim SR, Cantrell M, et al: Generation of biologically active interleukin-lp by proteolytic cleavage of the inactive precursor. J Biol Chem 263:9437-9442, 1988 25. Bone RC: Gram-negative sepsis: Background, clinical features, and intervention. Chest 100802-808, 1991 26. Bone RC: The pathogenesis of sepsis [review]. Ann Intern Med 115:457469,1991 27. Boraschi D, Villa L, Ghiara P, et al: Mechanism of acute toxicity of IL-1p in mice. Eur Cytokine Nehv 261-67, 1991 28. Borden EC, Chin P: Interleukin-6: A cytokine with potential diagnostic and therapeutic roles [review]. J Lab Clin Med 123824-829, 1994 29. Burger D, Chichportice R, Giri JG, et al: The inhibitory activity of human interleukin-1 receptor antagonist is enhanced by type I1 interleukin-1 soluble receptor and hindered by type I interleukin-1 soluble receptor. J Clin Invest 96:38-41, 1995 30. Burrell R Human responses to bacterial endotoxin [review]. Circ Shock 43:137-153, 1994 31. Camussi G, Mariano F, Biancone L, et a1 Lipopolysaccharide-binding protein and CD14 modulate the synthesis of platelet-activating factor by human monocytes and mesangial and endothelial cells stimulated with lipopolysaccharide. J Immunol 155316-324, 1995 32. Cannon JG, Tompkins RG, Gelfand JA, et al: Circulating interleukin-1 and tumor necrosis factor in septic shock and experimental endotoxin fever. J Infect Dis 161:7944, 1990 33. Car BD, Eng Vh4, Schnyder B, et al: Interferon-y receptor deficient mice are resistant to endotoxic shock. J Exp Med 179:1437-1444,1994 34. Carter DB, Deibel MR Jr, D ~ MCJ, et a1 Purification, cloning, expression and biological characterization of an interleukin-1 receptor antagonist protein. Nature 344:633-638,1990 35. Casey LC, Balk RA, Bone RC: Plasma cytokines and endotoxin levels correlate with survival in patients with the sepsis syndrome. Ann Intern Med 119571778, 1993 36. Cassatella MA, Meda L, Bonora S, et al: Interleukin10 (IL-10) inhibits the release of proinflammatory cytokines from human polymorphonuclear leukocytes. Evidence for an autocrine role of tumor necrosis factor and IL-lp in mediating the production of IL-8 triggered by lipopolysaccharide. J Exp Med 1782207-221 1, 1993 37. Castell JV,Gomez-Lechon MJ, David M, et al: Interleukin-6 is the major regulator of acute-phase protein synthesis in adult human hepatocytes. FEBS Lett 242:237-239, 1989 38. Centers for Disease Control: Increase in national hospital discharge rates for septicemia-United States. MMWR 3931-34, 1990 39. Cerretti DP, Kozlosky CJ, Mosley B, et al: Molecular cloning of the interleukin-lp converting enzyme. Science 256:97-100, 1992 40. Chang TW,Wu MH, Yang YJ: Blood levels of plate-

41.

42. 43.

44.

45.

46.

47. 48. 49.

50.

51. 52.

53.

54. 55. 56.

57.

58.

let-activating factor in endotoxin-sensitive and endotoxin-resistant mice during endotoxemia. J Formos Med Assoc 91:1133-1137,1992 Chernoff AE, Granowitz EV, Shapiro L, et al: A randomized, controlled trial of IL-10 in humans. Inhibition of inflammatory cytokine production and immune responses. J Immunol 1545492-5499, 1995 Colotta F, Re F, Muzio M, et a1 Interleukin-1 type I1 receptor: A decoy target for IL-1 that is regulated by IL-4. Science 261:472475, 1993 Coughlan AF, Hau H, Dunlop LC, et al: P-selectin and platelet-activating factor mediate initial endotoxin-induced neutropenia. J Exp Med 179:329-334, 1994 Cunha FQ, Moncada S, Liew FY Interleukin-10 (IL10) inhibits the induction of nitric oxide synthase by interferon-y in murine macrophages. Biochem Biophys Res Commun 182:1155-1159, 1992 Cunha FQ, Assreuy J, Moss DW, et al: Differential induction of nitric oxide synthase in various organs of the mouse during endotoxaemia: Role of TNF-a and IL-1p. Immunology 81:211-215, 1994 Cybulsky MI, Chan MKW, Movat Hz: Acute inflammation and microthrombosis induced by endotoxin, interleukin-1, and tumor necrosis factor and their implication in gram-negative infection. Lab Invest 58:365378, 1988 Damas P, Reuter A, Gysen P, et al: Tumor necrosis factor and interleukin-1 serum levels during severe sepsis in humans. Crit Care Med 17975-978, 1989 Darbonne WC, Rice GC, Mohler MA, et a 1 Red blood cells are a sink for interleukin 8, a leukocyte chemotaxin. J Clin Invest 88:1362-1369, 1991 Dayer J-M, Beutler B, Cerami A: Cachectin/tumor necrosis factor stimulates collagenase and prostaglandin-E2 production by human synovial cells and dermal fibroblasts. J Exp Med 162216%2168,1985 de Boer JP, Creasey AA, Chang A, et al: Activation of the complement system in baboons challenged with live Escherichia coli: Correlation with mortality and evidence for a biphasic activation pattern. Infect Immun 61:4293-4301, 1993 Deitch E A Bacterial translocation: The influence of dietary variables. Gut 35(suppl):S23-S27, 1994 Derkz B, Marchant A, Goldman M, et al: High levels of interleukin-10 during the initial phase of fulminant meningococcal septic shock. J Infect Dis 171:229-232,1995 Dhainaut JF, Tenaillon A, Le Tulzo Y, et a1 Plateletactivating factor receptor antagonist BN 52021 in the treatment of severe sepsis: A randomized, doubleblind, placebo-controlled, multicenter clinical trial. BN 52021 Sepsis Study Group. Crit Care Med 221720-1728, 1994 Dinarello C A Interleukin-1 and interleukin-1 antagonism. Blood 771627-1652, 1991 Dinarello CA: Interleukin-1 and the pathogenesis of the acute-phase response. N Engl J Med 311:14131418, 1984 Dinarello C A The proinflammatory cytokines interleukm-1 and tumor necrosis factor and treatment of the septic shock syndrome. J Infect Dis 163:11771184,1991 Dinarello CA, Cannon JG, Wolff SM, et al: Tumor necrosis factor (cachectin) is an endogenous pyrogen and induces production of interleukin 1. J Exp Med 1631433-1450,1986 Dobrina A, Schwartz BR, Carlos TM, et al: CDl1/ CDl8-independent neutrophil adherence to induc-

THE PATHOGENESIS OF SEPSIS ible endothelial-leucocyte adhesion molecules (ELAM) in vitro. Immunology 67502-508, 1989 59. Doe WF, Yang ST, Morrison DC,et al: Macrophage stimulation by bacterial lipopolysaccharides: 11. Evidence for differentiation signals delivered by lipid A and by a protein-rich fraction of lipopolysaccharides. J Exp Med 148:557-568,1978 60. Doherty DE, Zagarella L, Henson I'M, et al: Lipopolysaccharide stimulates monocyte adherence by effects on both the monocyte and the endothelial cell. J Immunol 1433673-3679,1989 61. Dripps DJ, Brandhuber BJ, Thompson RC, et a 1 Interleukin-1 (IL-1) receptor antagonist binds to the 80-kDa IL-1 receptor but does not initiate IL-1 signal transduction. J Biol Chem 26610331-10336, 1991 62. Durieux J-J, Vita N, Popescu 0, et a 1 The two soluble forms of the lipopolysaccharide receptor, CD14 Characterization and release by normal human monocytes. Eur J Immunol242006-2012, 1994 63. Eisenberg SP, Brewer MT, Verderber E, et al: Interleukin-1 receptor antagonist is a member of the interleukin-1 gene family: Evolution of a cytokine control mechanism. Proc Natl Acad Sci USA 885232-5236,1991 64. Eisenberg SP, Evans RJ, Arend WI', et a1 Primary structure and functional expression from complementary DNA of a human interleukin-1 receptor antagonist. Nature 343341-346, 1990 65. Elias JA, Lentz V. IL-1 and tumor necrosis factor synergistically stimulate fibroblast IL-6 production and stabilize IL-6 messenger RNA. J Immunol 145:161-166,1990 66. Enghild JJ, Thogersen IB, Salvesen G, et al: a-Macroglobulin from Limulus polyphemus exhibits proteinase inhibitory activity and participates in a hemolytic system. Biochemistry 29:10,07&10,080, 1990 67. Erickson SL, de Sauvage FJ, Kikly K, et a1 Decreased sensitivity to tumour necrosis factor but normal T-cell development in TNF receptor-2deficient mice. Nature 372560-563, 1994 68. Ertel W, Morrison MH, Wang P, et al: The complex pattern of cytokines in sepsis. Association between prostaglandins, cachectin, and interleukins. Ann SWg 214141-148,1991 69. Evans T, Carpenter A, Silva A, et al: Inhibition of nitric oxide synthase in experimental gram-negative sepsis. J Infect Dis 169:343-349, 1994 70. Evans TJ, Carpenter A, Moyes D, et al: Protective effects of a recombinant amino-terminal fragment of human bactericidal/permeability-increasingprotein in an animal model of gram-negative sepsis. J Infect Dis 171:153-160, 1995 71. Fabian TC, Croce MA, Stewart RM, et a 1 Neutrophil CD18 expression and blockade after traumatic shock and endotoxin challenge. Ann Surg 220:552-561, 1994 72. Feder LS, Laskin D L Regulation of hepatic endothelial cell and macrophage proliferation and nitric oxide production by GM-CSF, M-CSF, and IL-lP following acute endotoxemia. J Leukoc Biol55:507513, 1994 73. Feltis BA, Jechorek RP,Erlandsen SL, et al: Bacterial translocation and lipopolysaccharide-induced mortality in genetically macrophage-deficient op/op mice. Shock 2:29-33, 1994 74. Ferrero E, Jiao D, Tsuberi BZ, et al: Transgenic mice expressing human CD14 are hypersensitive to lipopolysaccharide. Proc Natl Acad Sci USA 90:23802384, 1993

193

75. Fisher CJ Jr, Dhainaut J-FA, Opal SM, et al: Recombinant human interleukin 1 receptor antagonist in the treatment of patients with sepsis syndrome: Results from a randomized, double-blind, placebocontrolled trial. JAMA 271:1836-1843, 1994 76. Fischer E, Marano MA, Van Zee KJ, et al: Interleukin-1 receptor blockade improves survival and hemodynamic performance in Escherichiu coli septic shock, but fails to alter host responses to sublethal endotoxemia. J Clin Invest 89:1551-1557, 1992 77. Fischer E, Van Zee KJ, Marano MA, et al: Interleukin-1 receptor antagonist circulates in experimental inflammation and in human disease. Blood 792196 2200,1992 78. Fong Y, Tracey KJ, Moldawer LL, et al: Antibodies to cachectin/tumor necrosis factor reduce interleukin-lp and interleukin 6 appearance during lethal bacteremia. J Exp Med 1701627-1633,1989 79. Fouqueray B, Boutard V, Philippe C, et al: Mesangial cell-derived interleukin-10 modulates mesangial cell response to lipopolysaccharide. Am J Pathol 14717&182,1995 80. Frank MM. Complement in the pathophysiology of human disease. N Engl J Med 3161525-1530, 1987 81. Fukatsu K, Saito H, Fukushima R, et al: Detrimental effects of a nitric oxide synthase inhibitor (N-omeganitro-L-arginine-methyl-ester) in a murine sepsis model. Arch Surg 130410-414,1995 82. Gazzano-Santoro H, Meszaros K, Birr C, et a1 Competition between rBPI23, a recombinant fragment of bactericidal/permeability-increasingprotein, and lipopolysaccharide (LPS)-binding protein for binding to LPS and gram-negative bacteria. Infect Immun 621185-1191, 1994 83. Gerard C, Bruyns C, Marchant A, et a1 Interleukin 10 reduces the release of tumor necrosis factor and prevents lethality in experimental endotoxemia. J Exp Med 177547-550, 1993 84. Gershenwald JE, Fong Y, Fahey TJ 111, et a1 Interleukin-1 receptor blockade attenuates the host inflammatory response. Proc Natl Acad Sci USA 874966-4970, 1990 85. Ghezzi P, Dinarello C A IL-1 induces IL-1: 111. Specific inhibition of IL-1 production by IFN-y. J Immuno1 140:42384244, 1988 86. Giri JG, Wells J, Dower SK, et al: Elevated levels of the shed type I1 IL-1 receptor in sepsis: Potential role for type I1 receptor in regulation of IL-I responses. J IIIUIIUIIO~ 153~5802-5809,1994 87. Go LL, Healey PJ, Watkins SC, et al: The effect of endotoxin on intestinal mucosal permeability to bacteria in vitro. Arch Surg 130:53-58, 1995 88. Golenbock DT, Bach RR, Lichenstein H, et al: Soluble CD14 promotes LPS activation of CD14-deficient PNH monocytes and endothelial cells. J Lab Clin Med 125:662-671, 1995 89. Gomez-Jimenez J, Martin MC, Sauri R, et al: Interleukin-10 and the monocyte/macrophage-induced inflammatory response in septic shock. J Infect Dis 17k472-475, 1995 90. Graham RM, Strahan ME, Norman KW, et al: Platelet and plasma platelet-activating factor in sepsis and myocardial infarction. Journal of Lipid Mediators & Cell Signalling 9:167-182, 1994 91. Granowitz EV, Clark BD, Vannier E, et al: Effect of interleukin-1 (IL-1) blockade on cytokine synthesis: I. IL-1 receptor antagonist inhibits IL-1-induced cytokine synthesis and blocks the binding of IL-1 to its type-I1 receptor on human monocytes. Blood 79:2356-2363, 1992

194

MARSH & WEWERS

92. Granowitz EV, Santos AA, Poutsiaka DD, et al: Production of interleukin-1-receptor antagonist during experimental endotoxaemia. Lancet 338142S1424, 1991 93. Granowitz EV, Vannier E, Poutsiaka DD, et a 1 Effect of interleukin-1 (IL-1) blockade on cytokine synthesis: 11. IL-1 receptor antagonist inhibits lipopolysaccharide-induced cytokine synthesis by human monocytes. Blood 79:2364-2369, 1992 94. Hannum CH, Wilcox CJ, Arend WP, et a 1 Interleukin-1 receptor antagonist activity of a human interleukin-1 inhibitor. Nature 343:336-340, 1990 95. Hart PH, Whitty GA, Piccoli DS, et a1 Synergistic activation of human monocytes by granulocytemacrophage colony-stimulating factor and INF-.I: Increased TNF-a but not IL-1 activity. J Immunol 141:1516-1521,1988 96. Haziot A, Chen S, Ferrero E, et al: The monocyte differentiation antigen, CD14, is anchored to the cell membrane by a phosphatidylinositol linkage. J Immun01 141:547-552, 1988 97. Hazuda D, Webb RL, Simon P, et a 1 Purification and characterization of human recombinant precursor interleukin-lp. J Biol Chem 264:1689-1692, 1989 98. Hempel L, Korholz D, Bonig H, et al: Interleukin10 directly inhibits the interleukin-6 production in T-cells. Scand J Immunol 4k462-466, 1995 99. Henderson W R The role of leukotrienes in inflammation. Ann Intern Med 121:684-697,1994 100. Henricson BE, Neta R, Vogel S N An interleukin-1 receptor antagonist blocks lipopolysaccharide-induced colony-stimulating factor production and early endotoxin tolerance. Infect Immun 59:11881191, 1991 101. Heremans H, Dillen C, Van Damme J, et a1 Essential role for natural killer cells in the lethal lipopolysaccharide-induced Shwartzman-like reaction in mice. Eur J Immunol241155-1160,1994 102. Heumann D, Gallay P, Barras C, et al: Control of lipopolysaccharide (LPS) binding and LPS-induced tumor necrosis factor secretion in human peripheral blood monocytes. J Immunol 148:3505-3512, 1992 103. Hollenberg SM, Cunnion RE, Zimmerberg J: Nitric oxide synthase inhibition reverses arteriolar hyporesponsiveness to catecholamines in septic rats. Am J Physiol264(pt 2):H660-H663, 1993 104. Howard M, Muchamuel T, Andrade S, et a1 Interleukin-10 protects mice from lethal endotoxemia. J Exp Med 177:1205-1208,1993 105. Jarvis GE, Evans RJ: Endotoxin-induced platelet aggregation in heparinised equine whole blood in vitro. Res Vet Sci 57317-324,1994 106. Kawamura M, Terashita Z, Imura Y, et al: Inhibitory effect of TCV-309, a novel platelet activating factor (PAF) antagonist, on endotoxin-induced disseminated intravascular coagulation in rats: Possible role of PAF in tissue factor generation. Thromb Res 70281-293, 1993 107. Kohler J, Heumann D, Garotta G, et al: IFN-y involvement in the severity of gram-negative infections in mice. J Immunol 151:916-921, 1993 108. Kopf M, Baumann H, Freer G, et a1 Impaired immune and acute-phase responses in interleukin-6deficient mice. Nature 368:339-342,1994 109. Lamas S, Michel T, Brenner BM, et al: Nitric oxide synthesis in endothelial cells: Evidence for a pathway inducible by TNF-a. Am J Physiol 261(pt 1):C634-C641, 1991 110. Lehner PJ, Davies KA, Walport MJ, et al: Meningo-

coccal septicaemia in a C6-deficient patient and effects of plasma transfusion on lipopolysaccharide release. Lancet 3401379-1381, 1992 111. Li P, Allen H, Banerjee S, et al: Mice deficient in ILlp-converting enzyme are defective in production of mature IL-1p and resistant to endotoxic shock. Cell 80401411, 1995 112. Libert C, Takahashi N, Cauwels A, et al: Response of interleukin-6-deficient mice to tumor necrosis factor-induced metabolic changes and lethality. Eur J Immun01 242237-2242,1994 113. Lorente JA, Landin L, Renes E, et a1 Role of nitric oxide in the hemodynamic changes of sepsis. Crit Care Med 21:759-767, 1993 114. Lund-Johansen F, Olweus J, Aarli AA, et a1 Signal transduction in human monocytes and granulocytes through the PI-linked antigen CD14. FEBS Lett 273:55-58, 1990 115. Mancilla J, Garcia P, Dinarello CA: IL-1 receptor antagonist can either protect or enhance the lethality of Klebsiella pneurnoniae sepsis in the newborn rat. Infect Immun 61:926-932, 1993 116. Marchant A, Bruyns C, Vandenabeele P, et al: Interleukin-10 controls interferon-y and tumor necrosis factor production during experimental endotoxemia. Eur J Immunol 24:1167-1171, 1994 117. Marchant A, Bruyns C, Vandenabeele P, et al: The protective role of interleukin-10 in endotoxin shock. Frog Clin Biol Res 388:417423, 1994 118. Marks JD, Marks CB, Luce JM, et al: Plasma tumor necrosis factor in patients with septic shock Mortality rate, incidence of adult respiratory distress syndrome, and effects of methylprednisolone administration. Am Rev Respir Dis 141:94-97, 1990 119. Marra MN, Wilde CG, Collins MS, et al: The role of bactericidal/permeability-increasingprotein as a natural inhibitor of bacterial endotoxin. J Immunol 148532-537, 1992 120. Marsh CB, Wewers M D Cytokine induced interleukin-1 receptor antagonist release in mononuclear phagocytes. Am J Respir Cell Mol Biol 10:521-525, 1994 121. Marsh CB, Pope HA, Wewers MD: Fcy cross-linking downregulates IL-lra and induces IL-1B in mononuclear phagocytes stimulated with endotoxin or Staphylococcus aureus. J Immunol 15246044611, 1994 122. Marsh CB, Gadek JE, Kindt GC, et al: Monocyte Fcy receptor cross-linking induces IL-8 production. J Imm~n01155~3161-3167,1995 123. Marsh CB, Moore SA, Pope HA, et al: Interleukin-1 receptor antagonist suppresses endotoxin induced interleukin-lp and tumor necrosis factor-a release from mononuclear phagocytes. Am J Physiol Lung Cell Mol Physiol 267L39445, 1994 124. Martich GD, Danner RL, Ceska M, et al: Detection of interleukin-8 and tumor necrosis factor in normal humans after intravenous endotoxin: The effect of antiinflammatory agents. J Exp Med 173:1021-1024, 1991 125. Marty C, Misset B, Tamion F, et al: Circulating interleukin-8 concentrations in patients with multiple organ failure or septic and non-septic origin. Crit Care Med 22673-679, 1994 126. Mathison JC, Wolfson E, Ulevitch RJ: Participation of tumor necrosis factor in the mediation of gramlipopolysaccharide-induced negative bacterial injury in rabbits. J Clin Invest 81:1925-1937,1988 127. McIntyre KW, Stepan GJ, Kolinsky KD, et al: Inhibi-

THE PATHOGENESIS OF SEPSIS tion of interleukin-1 (IL-1) binding and bioactivity in vitro and modulation of acute inflammation in vivo by IL-1 receptor antagonist and anti-IL-1 receptor monoclonal antibody. J Exp Med 173931939, 1991 128. McNamara MJ, Norton JA, Nauta RJ, et a 1 Interleukin-1 receptor antibody (IL-lab) protection and treatment against lethal endotoxemia in mice. J Surg Res 54:316-321, 1993 129. Michie HR, Manogue KR, Spriggs DR, et al: Detection of circulating tumor necrosis factor after endotoxin administration. N Engl J Med 318:1481-1486, 1988 130. Miles RH, Paxton TI', Dries DJ, et al: Interferony increases mortality following cecal ligation and puncture. J Trauma 36607-611,1994 131. Mohler KM, Torrance DS, Smith CA, et a 1 Soluble tumor necrosis factor (TNF) receptors are effective therapeutic agents in lethal endotoxemia and function simultaneously as both TNF carriers and TNF antagonists. J Immunol 151:1548-1561, 1993 132. Morin M, Schindler R, Wakabayashi G, et al: Picogram concentrations of endotoxin stimulate synthesis of IL-lp and TNF-a by human peripheral blood mononuclear cells exposed to recombinant human C5a. Eur Cytokine Netw 2:27-30, 1991 133. Mulligan MS, Jones ML, Bolanowski MA, et a 1 Inhibition of lung inflammatory reactions in rats by an anti-human IL-8 antibody. J Immunol 15055855595,1993 134. Munford RS, Hall C L Detoxification of bacterial lipopolysaccharides (endotoxins) by a human neutrophil enzyme. Science 2M203-205,1986 135. Murray HW: Interferon-y, the activated macrophage, and host defense against microbial challenge. Ann Intern Med 108:595-608,1988 136. Myers PR, Parker JL, Tanner MA, et al: Effects of cytokines tumor necrosis factor-a and interleukin l p on endotoxin-mediated inhibition of endotheliumderived relaxing factor bioactivity and nitric oxide production in vascular endothelium. Shock 1:7378, 1994 137. Nakae H, Endo S, Inada K, et al: Relationship between cytokines and leukotriene B4 in sepsis. Res Commun Chem Pathol Pharmacol 83:151-156, 1994 138. Nakane A, Minagawa T, Kato K Endogenous tumor necrosis factor (cachectin) is essential to host resistance against Lisferia monocytogenes infection. Infect Immun 562563-2569, 1988 139. Natanson C, Eichenholz PW, Danner RL, et al: Endotoxin and tumor necrosis factor challenges in dogs simulate the cardiovascular profile of human septic shock. J Exp Med 169:823-832,1989 140. Natanson C, Hoffman WD, Suffredini AF, et al: Selected treatment strategies for septic shock based on proposed mechanisms of pathogenesis. Ann Intern Med 120771-783, 1994 141. Nawroth PP, Bank I, Handley D, et al: Tumor necrosis factor/cachectin interacts with endothelial cell receptors to induce release of interleukin 1. J Exp Med 1631363-1375,1986 142. Niehorster M, Tiegs G, Schade UF: In vivo evidence for protease-catalyzed mechanism providing bioactive TNF-a. Biochem Pharmacol40:1601-1603, 1990 143. Niiro H, Otsuka T, Kuga S, et a 1 IL-10 inhibits prostaglandin-E2 production by lipopolysaccharidestimulated monocytes. Int Immunol 6:661464, 1994 144. Northoff H, Gluck D, Wolpl A, et a 1 Lipopolysaccharide-induced elaboration of interleukin-1 by

195

human monocytes: Use for detection of lipopolysaccharide in serum and the influence of serum-lipopolysaccharide interactions. Rev Infect Dis 9:5599S601,1987 145. OSullivan MG, Chilton FH, Huggins JEM, et a1 Lipopolysaccharide priming of alveolar macrophages for enhanced synthesis of prostanoids involves induction of a novel prostaglandin H synthase. J Biol Chem 26714547-14550, 1992 146. Ohlsson K, Bjork P, Bergenfeldt M, et al: Interleukin1 receptor antagonist reduces mortality from endotoxin shock. Nature 348:550-552, 1990 147. Oksusawa S, Gelfand JA, Ikejima T, et a 1 Interleukin-1 induces a shock-like state in rabbits: Synergism with tumor necrosis factor and the effect of cyclooxygenase inhibition. J Clin Invest 81:11621172, 1988 148. Parillo JE, Parker MM, Natanson C, et al: Septic shock in humans. Ann Intern Med 113227-242,1990 149. Pennica D, Nedwin GE, Hayflick JS, et al: Human tumour necrosis factor: Precursor structure, expression and homology to lymphotoxin. Nature 312724-729, 1984 150. Perera PY, Chen TY, Morrison DC,et al: Detection and analysis of the 80-kd lipopolysaccharide receptor in macrophages derived from LFS n and LPS d mice. J Leukocyte Biol51:501-506, 1992 151. Petros A, Lamb G, Leone A, et a1 Effects of a nitric oxide synthase inhibitor in humans with septic shock. Cardiovasc Res 2834-39, 1994 152. Pfeffer K, Matsuyama T, Kundig T, et al: Mice deficient for the 55-kd tumor necrosis factor receptor are resistant to endotoxic shock, yet succumb to L. monocytogenes infection. Cell 73457-497, 1993 153. Pugin J, Ulevitch RJ, Tobias PS: A critical role for monocytes and CD14 in endotoxin-induced endothelial cell activation. J Exp Med 178:2193-2200,1993 154. Raetz CRH, Ulevitch RJ, Wright SD, et a 1 Gramnegative endotoxin. An extraordinary lipid with profound effects on eukaryotic signal transduction. FASEB J 5~2652-2660, 1991 155. Ralph P, Nakoinz I, Sampson-Johannes A, et al: IL-10, T-lymphocyte inhibitor of human blood cell production of IL-1 and tumor necrosis factor. J Immunol 148808-814, 1992 156. Rankin JA, Sylvester I, Smith S, et al: Macrophages cultured in vitro release leukotriene-B, and neutrophi1 attractant/activation protein (interleukin-8) sequentially in response to stimulation with lipopolysaccharide and zymosan. J Clin Invest 8 6 1 5 5 6 1564,1990 157. Rathanaswami P, Hachicha M, Wong WL, et a 1 Synergistic effect of interleukin-lp and tumor necrosis factor-a on interleukin-8 gene expression in synovial fibroblasts. Evidence that interleukin-8 is the major neutrophil-activating chemokine released in response to monokine activation. Arthritis Rheum 361295-1304, 1993 158. Rogy MA, Auffenberg T, Espat NJ, et al: Human tumor necrosis factor receptor (p55) and interleukin10 gene transfer in the mouse reduces mortality to lethal endotoxemia and also attenuates local inflammatory responses. J Exp Med 181:2289-2294, 1995 159. Ruoslahti E Integrins. J Clin Invest 87:l-5, 1991 160. Scheld WM, Mandell GL: Nosocomial pneumonia: Pathogenesis and recent advances in diagnosis and therapy [review]. Rev Infect Dis 13(suppl 9):S743S751, 1991

196

MARSH & WEWERS

161. Schilling J, Cakmakci M, Battig U, et a 1 A new approach in the treatment of hypotension in human septic shock by NG-monomethyl-L-arginine, an inhibitor of the nitric oxide synthetase. Intensive Care Med 19:227-231, 1993 162. Schindler R, Gelfand JA, Dinarello CA: Recombinant C5a stimulates transcription rather than translation of interleukin-1 (IL-1) and tumor necrosis factor: Translational signal provided by lipopolysaccharide or IL-1 itself. Blood 761631-1638, 1990 163. Schletter J, Brade H, Brade L, et al: Binding of lipopolysaccharide (LPS) to an 80-kilodalton membrane protein of human cells is mediated by soluble CD14 and LPS-binding protein. Infect Immun 63:25762580, 1995 164. Schulz R, Panas DL, Catena R, et al: The role of nitric oxide in cardiac depression induced by interleukin-lp and tumour necrosis factor-a. Br J Pharmacol114:27-34,1995 165. Schumann RR, Leong SR, Flaggs GW, et al: Structure and function of lipouolvsaccharide binding protein. Science 2491429:1631,'1990 166. Simmons DL, Tan S, Tenen DG, et a1 Monocyte antigen CD14 is a phospholipid anchored membrane protein. Blood 733284-289, 1989 167. Simonet WS, Hughes TM, Nguyen TM, et al: Longterm impaired neutrophil migration in mice overexpressing human interleukin-8. J Clin Invest 94:13101319, 1994 168 Smith JW, Urba WJ, Curti BD, et al: The toxic and hematologic effects of interleukin-la administered in a phase I trial of patients with advanced hematologic malignancies. J Clin Oncol 10:1140-1152, 1992 169 St. John RC, Mizer LA, Kindt GC, et al: Acid aspiration-induced acute lung injury causes leukocyte-dependent systemic organ injury. J Appl Physiol 741994-2003,1993 170. Strieter RM, Koch AE, Antony VB, et al: The immunopathology of chemotactic cytokines: The role of interleukin-8 and monocyte chemoathactant protein-1. J Lab Clin Med 123:183-197, 1994 171. Strieter RM, Kunkel SL, Showell HJ, et al: Endothelial cell gene expression of a neutrophil chemotactic factor by TNF-a, LPS, and IL-1p. Science 24314671469,1989 172. Stylianou E, ONeill LAJ, Rawlinson L, et a1 Interleukin-1 induces NF-KBthrough its type I but not its type I1 receptor in lymphocytes. J Biol Chem 26715836-15841, 1992 173. Sun X, Caplan MS, Hsueh W Tumour necrosis factor and endotoxin synergistically activate intestinal phospholipase-A2 in mice. Role of endogenous platelet-activating factor and effect of exogenous platelet-activating factor. Gut 3521.5219, 1994 174. Sun XM, Hsueh W: Platelet-activating factor produces shock, in vivo complement activation, and tissue injury in mice. J Immunol 147509-514, 1991 175. Sylvestre DL, Ravetch JV:Fc receptors initiate the Arthus reaction: Redefining the inflammatory cascade. Science 265:1095-1098, 1994 176. Szabo C, Wu CC, Mitchell JA, et al: Platelet-activating factor contributes to the induction of nitric oxide synthase by bacterial lipopolysaccharide. Circ Res 73:991-999, 1993 177. Takakuwa T, Endo S, Nakae H, et al: PAF acetylhydrolase and arachidonic acid metabolite levels in patients with sepsis. Res Comm Chem Pathol Pharmacol 84:283-290, 1994 178. Taveira AM, Kaulbach HC, Chuidan FS, et al: Brief v

report: Shock and multiple organ dysfunction after self-administration of salmonella endotoxin. N Engl J Med 328:1457-1460, 1993 179. Thomberry NA, Bull HG, Calaycay JR, et al: A novel heterodimeric cysteine protease is required for interleukin-lp processing in monocytes. Nature 35676S774, 1992 180. Tiao G, Rafferty J, Ogle C, et a 1 Detrimental effect of nitric oxide synthase inhibition during endotoxemia may be caused by high levels of tumor necrosis factor and interleukin-6. Surgery 116:332-337, 1994 181. Tobias PS, Soldau K, Ulevitch RJ: Isolation of a lipopolysaccharide-binding acute-phase reactant from rabbit serum. J Exp Med 164:777-793, 1986 182. Tobias PS, McAdam KF'WJ, Soldau K, et al: Control of lipopolysaccharidehigh-densitylipoprotein interactions by an acute-phase reactant in human serum. Infect h u n 50:73-76, 1985 183. Tracey KJ, Cerami A: Tumor necrosis factor: An updated review of its biology. Crit Care Med 215215-5422, 1993 184. Tracey KJ, Beutler B, Lowry SF, et al: Shock and tissue injury induced by recombinant human cachectin. Science 2a470-474, 1986 185. Tracey KJ, Fong Y, Hesse DG, et al: Anti-cachectin/ TNF monoclonal antibodies prevent septic shock during lethal bacteraemia. Nature 330:662-664,1987 186. Tumbull RG, Talbot JA, Hamilton S M Hemodynamic changes and gut barrier function in sequential hemorrhagic and endotoxic shock. J Trauma 38:705712, 1995 187. Ungureanu-Longrois D, Balligand JL, Kelly RA, et al: Myocardial contractile dysfunction in the systemic inflammatory response syndrome: Role of a cytokine-inducible nitric oxide synthase in cardiac myocytes. J Mol Cell Cardiol27155-167, 1995 188. Van d e Winkel JGJ, Anderson C L Biology of human immunoglobulin G Fc receptors. J Leukoc Biol 49:511-524, 1991 189. van der Poll T, Buller HR, ten Cate H, et al: Activation of coagulation after administration of tumor necrosis factor to normal subjects. N Engl J Med 322: 1622-1627, 1990 190. Van Dervort AL, Yan L, Madara PJ, et al: Nitric oxide regulates endotoxin-induced TNF-a production by human neutrophils. J Immunol 152:41024109, 1994 191. Waage A, Brandtzaeg P, Espevik T, et al: Current understanding of the pathogenesis of gram-negative shock [review]. Infect Dis Clin North Am 5:781791, 1991 192. Waage A, Brandtzaeg P, Halstensen A, et al: The complex pattern of cytokines in serum from patients with meningococcal septic shock. J Exp Med 169333-338,1989 193. Wakabayashi G, Gelfand JA, Burke JF, et a1 A specific receptor antagonist for interleukin-1 prevents Escherichia coli-induced shock in rabbits. FASEB J 5:338-343, 1991 194. Warren HS, Glennon ML, Wainwright N, et al: Binding and neutralization of endotoxin by LimuZus antilipopolysaccharide factor. Infect Immun 60:2506-2513, 1992 195. Weiss J, Elsbach P, Shu C, et a]: Human bactericidal/permeability-increasing protein and a recombinant NH2-terminal fragment cause killing of serum-resistant gram-negative bacteria in whole blood and inhibit tumor necrosis factor release induced by the bacteria. J Clin Invest 90:1122-1130, 1992

THE PATHOGENESIS OF SEPSIS 196. Wewers MD, Rinehart JJ, She Z-W, et al: Tumor necrosis factor infusions in humans prime neutrophils for hypochlorous acid production. Am J Physiol Lung Cell Mol Physiol 259:L276-L282, 1990 197. Wilde CG, Seilhamer JJ, McGrogan M, et al: Bactericidal/permeability-increasingprotein and lipopolysaccharide (LPS)-binding protein. LPS binding properties and effects on LPS-mediated cell activation. J Biol Chem 26917411-17416, 1994 198. Wright SD, Ramos RA, Pate1 M, et a1 Septin: A factor in plasma that opsonizes lipopolysaccharidebearing particles for recognition by CD14 on phagocytes. J Exp Med 176719-727,1992 199. Wright SD, Ramos RA, Tobias PS, et a1 CD14, a receptor for complexes of lipopolysaccharide (LPS) and LPS binding protein. Science 249:1431-1433, 1990

197

200. Wurfel MM, Kunitake ST, Lichenstein H, et al: Lipopolysaccharide (LPS)-binding protein is carried on lipoproteins and acts as a cofactor in the neutralization of LPS. J Exp Med 180:1025-1035, 1994 201. Xu H, Gonzalo JA, St Pierre Y, et a1 Leukocytosis and resistance to septic shock in intercellular adhesion molecule ldeficient mice. J Exp Med 180:95-109,1994 202. Ye K, Koch KC, Clark BD, et al: Interleukin-1 downregulates gene and surface expression of interleukin-1 receptor type I by destabilizing its mRNA, whereas interleukin-'2 increases its expression. Immunology 75:427-434, 1992 203. Ziegler EJ, Fisher CJ, Sprung CL, et al: Treatment of gram-negative bacteremia and septic shock with HA-1A human monoclonal antibody against endotoxin: A randomized, double-blind, placebo-controlled trial. N Engl J Med 324429436,1991 Address reprint requests to Clay B. Marsh, MD Division of Pulmonary and Critical Care Medicine Ohio State University Medical Center N-325 Means Hall 1654 Upham Drive Columbus, OH 43210