Rats were subjected to acute lung injury by the intra-alveolar formation of IgG immune complexes of bovine serum albumin (BSA) and anti-BSA. In this model of injury, complement activation occurs and large numbers of neutrophils invade the interstitium and alveolar space. In the present study, animals were treated with intratracheal catalase concomitantly with anti-BSA or after a lag period of 5–120 min. Catalase treatment at time-zero or at 5 min post injury failed to prevent lung injury as indicated by permeability change, histological features, and neutrophil influx. However, treatment after a delay of 15–30 min (but not 120 min) afforded substantial protection. Consistent with past findings [19], lung injury was accompanied by an accumulation of matrix metalloproteinase 9 (MMP-9) in bronchoalveolar lavage (BAL) fluid. There was a strong correlation between inhibition of injury and reduction in MMP-9 levels. In vitro studies conducted in parallel revealed that unstimulated alveolar macrophages did not produce measurable MMP-9, while there was a large induction following exposure to the same immune complexes that initiated injury in vivo. MMP-2 was also slightly upregulated under the same conditions. Concomitant treatment with catalase greatly inhibited MMP-9 production by macrophages in response to immune complexes, but this treatment had little effect on basal production of either MMP-9 or MMP-2 by macrophage. The same concentration of catalase that suppressed MMP-9 elaboration also inhibited the production of tumor necrosis factor α. In contrast, when neutrophils were treated with catalase and then exposed to immune complexes, the antioxidant failed to prevent the release of either MMP-2 or MMP-9. Taken together, these findings demonstrate that antioxidant treatment interferes with elaboration of MMPs by alveolar macrophages. Protection against lung injury is correlated with reduction in MMP levels in the BAL fluid.

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.

Inflammatory lung injury is probably regulated by the balance between proteases and protease inhibitors together with oxidants and antioxidants, and proinflammatory and anti-inflammatory cytokines. Rat tissue inhibitor of metalloprotease-2 (TIMP-2) and secreted leukoprotease inhibitor (SLPI) were cloned, expressed, and shown to be up-regulated at the levels of mRNA and protein during lung inflammation in rats induced by deposition of IgG immune complexes. Using immunoaffinity techniques, endogenous TIMP-2 in the inflamed lung was shown to exist as a complex with 72- and 92-kDa metalloproteinases (MMP-2 and MMP-9). In inflamed lung both TIMP-2 and SLPI appeared to exist as enzyme inhibitor complexes. Lung expression of both TIMP-2 and SLPI appeared to involve endothelial and epithelial cells as well as macrophages. To assess how these endogenous inhibitors might affect the lung inflammatory response, animals were treated with polyclonal rabbit Abs to rat TIMP-2 or SLPI. This intervention resulted in significant intensification of lung injury (as revealed by extravascular leak of albumin) and substantially increased neutrophil accumulation, as determined by cell content in bronchoalveolar lavage (BAL) fluids. These events were correlated with increased levels of C5a-related chemotactic activity in BAL fluids, while BAL levels of TNF-alpha and chemokines were not affected by treatment with anti-TIMP-2 or anti-SLPI. The data suggest that endogenous TIMP-2 and SLPI dynamically regulate the intensity of lung inflammatory injury, doing so at least in part by affecting the generation of the inflammatory mediator, C5a.

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-1 alpha and monocyte chemoattractant-l) 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.

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.

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.

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.

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.

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 I-125-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 Ist 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 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.