Role of CC chemokines (macrophage inflammatory protein-1 beta, monocyte chemoattractant protein-1, RANTES) in acute lung injury in rats

The role of the CC chemokines, macrophage inflammatory protein-1 beta (MIP-1 beta), monocyte chemotactic peptide-1 (MCP-1), and RANTES, in acute lung inflammatory injury induced by intrapulmonary deposition of IgG immune complexes injury in rats was determined. Rat MIP-1 beta, MCP-1, and RANTES were cloned, the proteins were expressed, and neutralizing Abs were developed. mRNA and protein expression for MIP-1 beta and MCP-1 were up-regulated during the inflammatory response, while mRNA and protein expression for RANTES were constitutive and unchanged during the inflammatory response. Treatment of rats with anti-MIP-1 beta Ab significantly decreased vascular permeability by 37% (p = 0.012), reduced neutrophil recruitment into lung by 65% (p = 0.047), and suppressed levels of TNF-alpha in bronchoalveolar lavage fluids by 61% (p = 0.008). Treatment of rats with anti-rat MCP-1 or anti-rat RANTES had no effect on the development of lung injury. In animals pretreated intratracheally with blocking Abs to MCP-1, RANTES, or MIP-1 beta, significant reductions in the bronchoalveolar lavage content of these chemokines occurred, suggesting that these Abs had reached their targets. Conversely, exogenously MIP-1 beta, but not RANTES or MCP-1, caused enhancement of the lung vascular leak. These data indicate that MIP-1 beta, but not MCP-1 or RANTES, plays an important role in intrapulmonary recruitment of neutrophils and development of lung injury in the model employed. The findings suggest that in chemokine-dependent inflammatory responses in lung CC chemokines do not necessarily demonstrate redundant function.

Regulatory effects of interleukin-11 during acute lung inflammatory injury

The role of interleukin-11 (IL-11) was evaluated in the IgG immune complex model of acute lung injury in rats. IL-11 mRNA and protein were both up-regulated during the course of this inflammatory response. Exogenously administered IL-11 substantially reduced, in a dose-dependent manner, the intrapulmonary accumulation of neutrophils and the lung vascular leak of albumin. These in vivo anti-inflammatory effects of IL-11 were associated with reduced NF-kappaB activation in lung, reduced levels of tumor necrosis factor alpha (TNF-alpha) in bronchoalveolar lavage (BAL) fluids, and diminished up-regulation of lung vascular ICAM-1. It is interesting that IL-11 did not affect BAL fluid content of the CXC chemokines, macrophage inflammatory protein-2 (MIP-2) and cytokine-inducible neutrophil chemoattractant (CINC); the presence of IL-11 did not affect these chemokines. However, BAL content of C5a was reduced by IL-11. These data indicate that IL-11 is a regulatory cytokine in the lung and that, like other members of this family, its anti-inflammatory properties appear to be linked to its suppression of NF-kappaB activation, diminished production of TNF-alpha, and reduced up-regulation of lung vascular ICAM-1.

Protective effects of C5a blockade in sepsis

Sepsis in humans is a difficult condition to treat and is often associated with a high mortality rate. In this study, we induced sepsis in rats using cecal ligation and puncture (CLP). In rats depleted of the complement factor C3, CLP led to very short survival times (about 4 days). Of the rats that underwent CLP ('CLP rats') that were C3-intact and treated with preimmune IgG, most (92%) were dead by 7 days. Blood neutrophils from these rats contained on their surfaces the powerful complement activation product C5a. This group had high levels of bacteremia, and their blood neutrophils when stimulated in vitro had greatly reduced production of H2O2, which is known to be essential for the bactericidal function of neutrophils. In contrast, when companion CLP rats were treated with IgG antibody against C5a, survival rates were significantly improved, levels of bacteremia were considerably reduced, and the H2O2 response of blood neutrophils was preserved. Bacterial colony-forming units in spleen and liver were very high in CLP rats treated with preimmune IgG and very low in CLP rats treated with IgG antibody against C5a, similar to values obtained in rats that underwent 'sham' operations (without CLP). These data indicate that sepsis causes an excessive production of C5a, which compromises the bactericidal function of neutrophils. Thus, C5a may be a useful target for the treatment of sepsis.

Synergistic enhancement of chemokine generation and lung injury by C5a or the membrane attack complex of complement

Complement plays an important role in many acute inflammatory responses. In the current studies it was demonstrated that, in the presence of either C5a or sublytic forms of the complement-derived membrane attack complex (MAC), rat alveolar macrophages costimulated with IgG immune complexes demonstrated synergistic production of C-X-C (macrophage inflammatory protein-2 and cytokine-induced neutrophil chemoattractant) and C-C (macrophage inflammatory protein-1alpha and monocyte chemoattractant-1) chemokines. In the absence of the costimulus, C5a or MAC did not induce chemokine generation. In in vivo studies, C5a and MAC alone caused limited or no intrapulmonary generation of chemokines, but in the presence of a costimulus (IgG immune complexes) C5a and MAC caused synergistic intrapulmonary generation of C-X-C and C-C chemokines but not of tumor necrosis factor alpha. Under these conditions increased neutrophil accumulation occurred, as did lung injury. These observations suggest that C5a and MAC function synergistically with a costimulus to enhance chemokine generation and the intensity of the lung inflammatory response.

Mechanisms of enhanced lung injury during sepsis

A major complication in sepsis is progressively impaired lung function and susceptibility to intrapulmonary infection. Why sepsis predisposes the lung to injury is not clear. In the current studies, rats were rendered septic by cecal ligation/puncture and evaluated for increased susceptibility to injury after a direct pulmonary insult (deposition of IgG immune complexes or airway instillation of lipopolysaccharide). By itself, cecal ligation/puncture did not produce evidence of lung injury. However, after a direct pulmonary insult, lung injury in septic animals was significantly enhanced. Enhanced lung injury was associated with increased accumulation of neutrophils in lung, enhanced production of CXC chemokines (but not tumor necrosis factor-alpha) in bronchoalveolar lavage fluids, and increased expression of lung vascular intercellular adhesion molecule-1 (ICAM-1). Complement depletion or treatment with anti-C5a abolished all evidence of enhanced lung injury in septic animals. When stimulated in vitro, bronchoalveolar lavage macrophages from septic animals had greatly enhanced CXC chemokine responses as compared with macrophages from sham-operated animals or from septic animals that had been complement depleted. These data indicate that the septic state causes priming of lung macrophages and suggest that enhanced lung injury in the septic state is complement dependent and related to increased production of CXC chemokines.

Essential role of alveolar macrophages in intrapulmonary activation of NF-kappaB

Acute inflammatory injury in rat lung induced by deposition of immunoglobulin G immune complexes requires expression of cytokines and chemokines as well as activation of the transcription factor nuclear factor (NF)-kappaB. There is little direct evidence regarding the role of alveolar macrophages in these activation events. In the present studies, rat lungs were depleted of alveolar macrophages by airway instillation of liposome-encapsulated dichloromethylene diphosphonate. These procedures, which greatly reduced the number of retrievable alveolar macrophages, suppressed activation of lung NF-kappaB in the inflammatory model. In addition, bronchoalveolar lavage levels of tumor necrosis factor-alpha (TNF-alpha) and the CXC chemokine, macrophage inflammatory protein-2, were substantially reduced. In parallel, upregulation of the lung vascular adhesion molecule, intercellular adhesion molecule-1, was greatly reduced by intrapulmonary instillation of phosphonate-containing liposomes. Neutrophil accumulation and development of lung injury were also substantially diminished. Lung instillation of TNF-alpha in alveolar macrophage-depleted rats restored the NF-kappaB activation response in whole lung. These data suggest that, in this inflammatory model, initial activation of NF-kappaB occurs in alveolar macrophages and the ensuing production of TNF-alpha may propagate NF-kappaB activation to other cell types in the lung.

In vitro and in vivo dependency of chemokine generation on C5a and TNF-alpha

Under a variety of conditions, alveolar macrophages can generate early response cytokines (TNF-alpha, IL-1), complement components, and chemotactic cytokines (chemokines). In the current studies, we determined the requirements for TNF-alpha and the complement activation product C5a in chemokine production in vitro and in vivo. Two rat CXC chemokines (macrophage inflammatory protein (MIP)-2 and cytokine-induced neutrophil chemoattractant (CINC)) as well as three rat CC chemokines (MIP-1alpha, MIP-1beta, and monocyte chemoattractant protein (MCP)-1) were investigated. Chemokine generation in vitro was studied in rat alveolar macrophages stimulated with IgG immune complexes in the absence or presence of Abs to TNF-alpha or C5a. The rat lung injury model induced by IgG immune complex deposition was employed for in vivo studies. Abs to TNF-alpha or C5a were administered intratracheally or i.v., and effects on chemokine levels in bronchoalveolar lavage fluids were quantitated by ELISA. Both in vitro and in vivo studies demonstrated the requirements for TNF-alpha and C5a for full generation of CXC and CC chemokines. In vitro and in vivo blockade of TNF-alpha or C5a resulted in significantly reduced production of chemokines. Supernatant fluids from in vitro-stimulated macrophages revealed by Western blot analysis the presence of C5a/C5adesArg, indicating intrinsic generation of C5a/C5adesArg by alveolar macrophages and explaining the higher efficiency of intratracheal vs i.v. blockade of C5a in reducing chemokine production. These results underscore the central role of both TNF-alpha and C5a, which appear to function as autocrine activators to promote CXC and CC chemokine generation by alveolar macrophages.

Regulation of acute lung inflammatory injury by endogenous IL-13

Using IgG immune complex deposition to trigger acute lung inflammation in rats, we have previously shown that exogenously administered IL-13 suppresses the acute inflammatory response. In the same model, expression of both mRNA and protein for IL-13 has now been detected. Treatment of rats with Ab to IL-13 accentuated the inflammatory response, with significant increases in lung vascular permeability and in the number of neutrophils in bronchoalveolar lavage fluids. In the presence of anti-IL-13, activation of the transcription factor, NF-kappaB, was significantly increased in lung. In addition, anti-IL-13 caused significant increases in bronchoalveolar lavage levels of TNF-alpha, macrophage inflammatory protein-2, and cytokine-inducible neutrophil chemoattractant but no changes in lung vascular ICAM-1. These data suggest that during lung inflammation endogenous IL-13 regulates NF-kappaB activation and related cytokine/chemokine generation, all of which determines the intensity of the lung inflammatory response.

Inhibition of NF-kappaB activation and augmentation of IkappaBbeta by secretory leukocyte protease inhibitor during lung inflammation

In earlier experiments, exogenous administration of secretory leukocyte protease inhibitor (SLPI) suppressed acute lung injury induced by deposition of IgG immune complexes. In the current studies we examined the mechanism of the protective effects of SLPI in this model. The presence of SLPI in the IgG immune complex-model of lung injury reduced the increase in extravascular leakage of 125I-albumin, the intensity of up-regulation of lung vascular intercellular adhesion molecule-1, and the numbers of neutrophils accumulating in the lung. The presence of SLPI caused greatly reduced activation (ie, nuclear translocation) of the transcription nuclear factor-kappaB (NF-kappaB) in lung cells but did not suppress activation of lung mitogen-activated protein kinase. SLPI did not alter NF-kappaB activation in alveolar macrophages harvested 30 minutes after initiation of lung inflammation. In the presence of SLPI, content of tumor necrosis factor-alpha, CXC chemokines, and C5a in bronchoalveolar fluids was unaffected. In the inflamed lungs, inhibition of NF-kappaB activation by SLPI was associated with elevated levels of lung IkappaBbeta (but not IkappaBalpha) protein in the absence of elevated mRNA for IkappaBbeta. When instilled into normal lung, SLPI also caused similar changes (increases) in lung IkappaBbeta. Finally, in the lung inflammatory model used, the presence of anti-SLPI caused accentuated activation of NF-kappaB. These data confirm the anti-inflammatory effect of SLPI in lung and point to a mechanism of anti-inflammatory effects of SLPI. SLPI appears to function as an endogenous regulator of lung inflammation.

Roles for C-X-C chemokines and C5a in lung injury after hindlimb ischemia-reperfusion

We evaluated the roles of the C-X-C chemokines cytokine-induced neutrophil chemoattractant (CINC) and macrophage inflammatory protein-2 (MIP-2) as well as the complement activation product C5a in development of lung injury after hindlimb ischemia-reperfusion in rats. During reperfusion, CD11b and CD18, but not CD11a, were upregulated on neutrophils [bronchoalveolar lavage (BAL) and blood] and lung macrophages. BAL levels of CINC and MIP-2 were increased during the ischemic and reperfusion periods. Treatment with either anti-CINC or anti-MIP-2 IgG significantly reduced lung vascular permeability and decreased lung myeloperoxidase content by 93 and 68%, respectively (P < 0.05). During the same period, there were significant increases in serum C5a-related neutrophil chemotactic activity. Treatment with anti-C5a decreased lung vascular permeability, lung myeloperoxidase, and BAL CINC by 51, 58, and 23%, respectively (P < 0.05). The data suggest that the C-X-C chemokines CINC and MIP-2 as well as the complement activation product C5a are required for lung neutrophil recruitment and full induction of lung injury after hindlimb ischemia-reperfusion in rats.

Mediators of microvascular injury in dermal burn wounds

In previous studies we have demonstrated that second-degree thermal injury of skin in rats leads to secondary effects, such as systemic complement activation, C5a-mediated activation of blood neutrophils, their adhesion-molecule-guided accumulation in lung capillaries and the development of acute pulmonary injury, largely caused by neutrophil-derived toxic oxygen metabolites. In the dermal burn wound, however, pathophysiologic events are less well understood. The injury is fully developed at four hours post-burn. To further elucidate the pathogenesis of the "late phase" dermal vascular damage, rats were depleted of neutrophils or complement by pretreatment with rabbit antibody against rat neutrophils or with cobra venom factor, respectively. In other experiments, rats were treated with blocking antibodies to IL-6, IL-1, and TNF alpha immediately following thermal burning or were pretreated with hydroxyl radical scavengers (dimethyl sulfoxide, dimethyl thiourea). Extravasation of 125I-labeled bovine serum albumin into the burned skin was studied, as well as, skin myeloperoxidase levels. The studies revealed that, like in secondary lung injury, neutrophils and toxic oxygen metabolites, are required for full development of microvascular injury. In contrast, however, development of dermal vascular damage in thermally injured rats was not affected by complement depletion. Our data suggest that the development of microvascular injury in the dermal burn wound is complement-independent, involves the pro-inflammatory cytokines IL-1, TNF alpha and IL-6, and may result from reactive oxygen metabolites generated by neutrophils accumulating in the burn wound.

Soluble ICAM-1 activates lung macrophages and enhances lung injury

Because of the important role of rat ICAM-1 in the development of lung inflammatory injury, soluble recombinant rat ICAM-1 (sICAM-1) was expressed in bacteria, and its biologic activities were evaluated. Purified sICAM-1 did bind to rat alveolar macrophages in a dose-dependent manner and induced production of TNF-alpha and the CXC chemokine, macrophage inflammatory protein-2 (MIP-2). Alveolar macrophages exhibited cytokine responses to both sICAM-1 and immobilized sICAM-1, while rat PBMCs failed to demonstrate similar responses. Exposure of alveolar macrophages to sICAM-1 resulted in NFkappaB activation (which was blocked by the presence of the aldehyde peptide inhibitor of 28S proteosome and by genistein, a tyrosine kinase inhibitor). As expected, cross-linking of CD18 on macrophages with Ab resulted in generation of TNF-alpha and MIP-2. This response was also inhibited in the presence of the proteosome inhibitor and by genistein. Alveolar macrophages showed adherence to immobilized sICAM-1 in a CD18-dependent manner. Finally, airway instillation of sICAM-1 intensified lung injury produced by intrapulmonary deposition of IgG immune complexes in a manner associated with enhanced lung production of TNF-alpha and MIP-2 and increased neutrophil recruitment. Therefore, through engagement of beta2 integrins, sICAM-1 enhances alveolar macrophage production of MIP-2 and TNF-alpha, the result of which is intensified lung injury after intrapulmonary disposition of immune complexes.

Differing patterns of P-selectin expression in lung injury

Using two models of acute lung inflammatory injury in rats (intrapulmonary deposition of immunoglobulin G immune complexes and systemic activation of complement after infusion of purified cobra venom factor), we have analyzed the requirements and patterns for upregulation of lung vascular P-selectin. In the immune complex model, upregulation of P-selectin was defined by Northern and Western blot analysis of lung homogenates, by immunostaining of lung tissue, and by vascular fixation of 125I-labeled anti-P-selectin. P-selectin protein was detected by 1 hour (long before detection of mRNA) and expression was sustained for the next 7 hours, in striking contrast to the pattern of P-selectin expression in the cobra venom factor model, in which upregulation was very transient (within the 1st hour). In the immune complex model, injury and neutrophil accumulation were P-selectin dependent. Upregulation of P-selectin was dependent on an intact complement system, and the presence of blood neutrophils was susceptible to the antioxidant dimethyl sulfoxide and required C5a but not tumor necrosis factor alpha. In contrast, in the cobra venom factor model, upregulation of P-selectin, which is C5a dependent, was also dimethyl sulfoxide sensitive but neutrophil independent. Different mechanisms that may explain why upregulation of lung vascular P-selectin is either transient or sustained are discussed.

Complement, cytokines, and adhesion molecule expression in inflammatory reactions

Directional emigration of neutrophils is the hallmark of phlogistic processes. The involved regulatory mechanisms include complement activation products, cytokines, adhesion molecules, and their respective counter receptors. In this article, we discuss the role of these mediators in initiation, development, and containment of acute inflammatory responses in in vitro and in vivo models, showing interactions between a network of proinflammatory and anti-inflammatory effectors. A major focus deals with the effects of complement on activation of the vascular endothelium. In addition, the role of interleukins in the regulation of inflammatory responses is described.

Role of complement in in vitro and in vivo lung inflammatory reactions

Complement is one of the integral buttresses of the inflammatory response. In addition to host defense activities, proinflammatory properties of several complement components are described. This overview elucidates the role of complement in inflammatory reactions in vitro and in vivo, focusing on the complement activation products, C5a, and the membrane attack complex, C5b-9. Using several approaches, the impact of these complement components in mechanisms relevant to neutrophil recruitment is emphasized. In addition, the participation of complement in endothelial superoxide generation and its essential requirement for full expression of lung injury is demonstrated, as are the involved intracellular signal transduction pathways. Understanding the mechanisms of complement-induced proinflammatory effects may provide a basis for future therapeutic blockade of complement and/or its activation products.

NF-kappaB activation during IgG immune complex-induced lung injury: requirements for TNF-alpha and IL-1beta but not complement

The development of acute lung inflammatory injury induced by alveolar deposition of IgG immune complexes in rats requires increased production of the proinflammatory cytokines, tumor necrosis factor-alpha (TNF-alpha), and interleukin-1beta (IL-1beta) as well as the complement activation product, C5a. Transcription of TNF-alpha and IL-1beta genes are known to be regulated by the nuclear factor-kappa B (NF-kappaB). During IgG immune complex-induced lung inflammation, NF-kappaB has been shown to be activated in both alveolar macrophages and whole lung tissues. In the current studies we sought to determine whether TNF-alpha, IL-1beta, the complement system and oxidants contribute to the activation of NF-kappaB in the lung. Electrophoretic mobility shift analysis of nuclear extracts from whole lung tissues demonstrated that NF-kappaB activation induced by the presence of IgG immune complexes occurred independently of the complement system and neutrophils. Intrapulmonary instillation of TNF-alpha or IL-1beta into normal lung induced NF-kappaB, whereas C5a was incapable of causing NF-kappaB activation. In alveolar macrophages stimulated in vitro with IgG immune complexes, NF-kappaB activation was greatly attenuated in the presence of antibodies to TNF-alpha or IL-1beta. Similarly, in vivo blockade of TNF-alpha or IL-1beta suppressed lung NF-kappaB activation during IgG immune complex-induced lung injury. N-acetylcysteine, but not catalase, suppressed activation of lung NF-kappaB. These data suggest that TNF-alpha and IL-1beta function in an autocrine or paracrine manner to amplify the lung inflammatory response through activation of NF-kappaB. Oxidants not derived from neutrophils also appear to play a role in this process, whereas complement activation products are not involved in this phenomenon.

Protective effects of an aptamer inhibitor of neutrophil elastase in lung inflammatory injury

Neutrophils play an important part in the development of acute inflammatory injury. Human neutrophils contain high levels of the serine protease elastase, which is stored in azurophilic granules and is secreted in response to inflammatory stimuli. Elastase is capable of degrading many components of extracellular matrix [1-4] and has cytotoxic effects on endothelial cells [5-7] and airway epithelial cells. Three types of endogenous protease inhibitors control the activity of neutrophil elastase, including alpha-1 protease inhibitor (alpha-1PI), alpha-2 macroglobulin and secreted leukoproteinase inhibitor (SLPI) [8-10]. A disturbed balance between neutrophil elastase and these inhibitors has been found in various acute clinical conditions (such as adult respiratory syndrome and ischemia-reperfusion injury) and in chronic diseases. We investigated the effect of NX21909, a selected oligonucleotide (aptamer) inhibitor of elastase, in an animal model of acute lung inflammatory disease [11-14]. This inhibitor was previously selected from a hybrid library of randomized DNA and a small-molecule irreversible inhibitor of elastase (a valine diphenyl ester phosphonate, Fig. 1), by the blended SELEX process [15]. We show that NX21909 inhibits lung injury and neutrophil influx in a dose-dependent manner, the first demonstration of efficacy by an aptamer in an animal disease model.