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

Complement as a vital nexus of the pathobiological connectome for acute respiratory distress syndrome: An emerging therapeutic target

The hallmark of acute respiratory distress syndrome (ARDS) pathobiology is unchecked inflammation-driven diffuse alveolar damage and alveolar-capillary barrier dysfunction. Currently, therapeutic interventions for ARDS remain largely limited to pulmonary-supportive strategies, and there is an unmet demand for pharmacologic therapies targeting the underlying pathology of ARDS in patients suffering from the illness. The complement cascade (ComC) plays an integral role in the regulation of both innate and adaptive immune responses. ComC activation can prime an overzealous cytokine storm and tissue/organ damage. The ARDS and acute lung injury (ALI) have an established relationship with early maladaptive ComC activation. In this review, we have collected evidence from the current studies linking ALI/ARDS with ComC dysregulation, focusing on elucidating the new emerging roles of the extracellular (canonical) and intracellular (non-canonical or complosome), ComC (complementome) in ALI/ARDS pathobiology, and highlighting complementome as a vital nexus of the pathobiological connectome for ALI/ARDS via its crosstalking with other systems of the immunome, DAMPome, PAMPome, coagulome, metabolome, and microbiome. We have also discussed the diagnostic/therapeutic potential and future direction of ALI/ARDS care with the ultimate goal of better defining mechanistic subtypes (endotypes and theratypes) through new methodologies in order to facilitate a more precise and effective complement-targeted therapy for treating these comorbidities. This information leads to support for a therapeutic anti-inflammatory strategy by targeting the ComC, where the arsenal of clinical-stage complement-specific drugs is available, especially for patients with ALI/ARDS due to COVID-19.

The Crucial Role of PPARγ-Egr-1-Pro-Inflammatory Mediators Axis in IgG Immune Complex-Induced Acute Lung Injury

Background

The ligand-activated transcription factor peroxisome proliferator-activated receptor (PPAR) γ plays crucial roles in diverse biological processes including cellular metabolism, differentiation, development, and immune response. However, during IgG immune complex (IgG-IC)-induced acute lung inflammation, its expression and function in the pulmonary tissue remains unknown.

Objectives

The study is designed to determine the effect of PPARγ on IgG-IC-triggered acute lung inflammation, and the underlying mechanisms, which might provide theoretical basis for therapy of acute lung inflammation.

Setting

Department of Pathogenic Biology and Immunology, Medical School of Southeast University

Subjects

Mice with down-regulated/up-regulated PPARγ activity or down-regulation of Early growth response protein 1 (Egr-1) expression, and the corresponding controls.

Interventions

Acute lung inflammation is induced in the mice by airway deposition of IgG-IC. Activation of PPARγ is achieved by using its agonist Rosiglitazone or adenoviral vectors that could mediate overexpression of PPARγ. PPARγ activity is suppressed by application of its antagonist GW9662 or shRNA. Egr-1 expression is down-regulated by using the gene specific shRNA.

Measures and Main Results

We find that during IgG-IC-induced acute lung inflammation, PPARγ expression at both RNA and protein levels is repressed, which is consistent with the results obtained from macrophages treated with IgG-IC. Furthermore, both in vivo and in vitro data show that PPARγ activation reduces IgG-IC-mediated pro-inflammatory mediators’ production, thereby alleviating lung injury. In terms of mechanism, we observe that the generation of Egr-1 elicited by IgG-IC is inhibited by PPARγ. As an important transcription factor, Egr-1 transcription is substantially increased by IgG-IC in both in vivo and in vitro studies, leading to augmented protein expression, thus amplifying IgG-IC-triggered expressions of inflammatory factors via association with their promoters.

Conclusion

During IgG-IC-stimulated acute lung inflammation, PPARγ activation can relieve the inflammatory response by suppressing the expression of its downstream target Egr-1 that directly binds to the promoter regions of several inflammation-associated genes. Therefore, regulation of PPARγ-Egr-1-pro-inflammatory mediators axis by PPARγ agonist Rosiglitazone may represent a novel strategy for blockade of acute lung injury.

Angiotensin-converting enzyme 2, the complement system, the kallikrein-kinin system, type-2 diabetes, interleukin-6, and their interactions regarding the complex COVID-19 pathophysiological crossroads

Because of the current COVID-19-pandemic, the world is currently being held hostage in various lockdowns. ACE2 facilitates SARS-CoV-2 cell-entry, and is at the very center of several pathophysiological pathways regarding the RAAS, CS, KKS, T2DM, and IL-6. Their interactions with severe COVID-19 complications (e.g. ARDS and thrombosis), and potential therapeutic targets for pharmacological intervention, will be reviewed.

The Cooperative Induction of CCL4 in Human Monocytic Cells by TNF-α and Palmitate Requires MyD88 and Involves MAPK/NF-κB Signaling Pathways

Chronic low-grade inflammation, also known as metabolic inflammation, is a hallmark of obesity and parallels with the presence of elevated circulatory levels of free fatty acids and inflammatory cytokines/chemokines. CCL4/MIP-1β chemokine plays a key role in the adipose tissue monocyte recruitment. Increased circulatory levels of TNF-α, palmitate and CCL4 are co-expressed in obesity. We asked if the TNF-α/palmitate could interact cooperatively to augment the CCL4 production in human monocytic cells and macrophages. THP-1 cells/primary macrophages were co-treated with TNF-α/palmitate and CCL4 mRNA/protein expression was assessed using qRT-PCR/ELISA. TLR4 siRNA, a TLR4 receptor-blocking antibody, XBlue™-defMyD cells and pathway inhibitors were used to decipher the signaling mechanisms. We found that TNF-α/palmitate co-stimulation augmented the CCL4 expression in monocytic cells and macrophages compared to controls (p < 0.05). TLR4 suppression or neutralization abrogated the CCL4 expression in monocytic cells. Notably, CCL4 cooperative induction in monocytic cells was: (1) Markedly less in MyD88-deficient cells, (2) IRF3 independent, (3) clathrin dependent and (4) associated with the signaling mechanism involving ERK1/2, c-Jun, JNK and NF-κB. In conclusion, TNF-α/palmitate co-stimulation promotes the CCL4 expression in human monocytic cells through the mechanism involving a TLR4-MyD88 axis and MAPK/NF-κB pathways. These findings unravel a novel mechanism of the cooperative induction of CCL4 by TNF-α and palmitate which could be relevant to metabolic inflammation.

2-Methoxyestradiol protects against IgG immune complex-induced acute lung injury by blocking NF-κB and CCAAT/enhancer-binding protein β activities

Increasing evidences indicate that 2-Methoxyestradiol (2ME2) plays an essential role in protecting against inflammatory responses. However, its effect on IgG immune complex (IC)-induced acute lung injury (ALI) remains enigmatic. In the study, by using i.p. administration of 2ME2, we evaluated its influence on IgG IC-induced pulmonary injury in mice. We found that during IgG IC-induced ALI, mice treated by 2ME2 displayed a substantial decrease in vascular permeability and neutrophil influx (represented by myeloperoxidase activity) when compared with their counterparts receiving vehicle treatment. Furthermore, 2ME2 treatment significantly decreased pro-inflammatory mediator production and inflammatory cell, especially neutrophil accumulation in bronchoalveolar lavage fluids (BALFs) upon IgG IC stimulation. In vitro, IgG IC-triggered inflammatory mediator production was markedly down-regulated by 2ME2 in macrophages. Moreover, we verified that the activation of the transcription factors, NF-κB and CCAAT/enhancer-binding protein (C/EBP) β, were inhibited by 2ME2 in IgG IC-challenged macrophages. We demonstrated that alleviation of NF-κB-dependent transcription might be associated with reduced phosphorylation of NF-κB p65, and reduction of C/EBP activation was directly linked to its expression. In addition, we discovered that IgG IC-stimulated phosphorylation of both p38 MAPK and ERK1/2 was alleviated by 2ME2. These data indicated a novel strategy for blockade of IgG IC-induced inflammatory activities.

Anti-inflammatory interventions-what has worked, not worked, and what may work in the future

Our Introductory Commentary relates to many topics that are linked to inflammatory responses and how these responses are regulated in order to promote healing of damaged tissues and bring about effective clearance of infectious agents. In non-infectious situations, cells and tissues release products (danger associated molecular patterns) that can trigger damaging inflammatory responses. These products must be effectively dealt with in order to avoid serious tissue injury. We provide a perspective about many decades of research into the inflammatory response and describe strategies that have achieved success in restraining inflammatory responses, as well as many approaches that have not been clinically effective. With development of new technologies such as advanced genomic analysis, highly sensitive and sophisticated mass spectrometry and related approaches, as well as the ability to employ mutagenesis induction, we are beginning to define highly sophisticated molecular pathways that previously were opaque. This progress may well have clinical relevance, and we may be on the edge of a scientific revolution in the broad area of inflammation.

Reconciling the IPC and Two-Hit Models: Dissecting the Underlying Cellular and Molecular Mechanisms of Two Seemingly Opposing Frameworks

Inflammatory cascades and mechanisms are ubiquitous during host responses to various types of insult. Biological models and interventional strategies have been devised as an effort to better understand and modulate inflammation-driven injuries. Amongst those the two-hit model stands as a plausible and intuitive framework that explains some of the most frequent clinical outcomes seen in injuries like trauma and sepsis. This model states that a first hit serves as a priming event upon which sequential insults can build on, culminating on maladaptive inflammatory responses. On a different front, ischemic preconditioning (IPC) has risen to light as a readily applicable tool for modulating the inflammatory response to ischemia and reperfusion. The idea is that mild ischemic insults, either remote or local, can cause organs and tissues to be more resilient to further ischemic insults. This seemingly contradictory role that the two models attribute to a first inflammatory hit, as priming in the former and protective in the latter, has set these two theories on opposing corners of the literature. The present review tries to reconcile both models by showing that, rather than debunking each other, each framework offers unique insights in understanding and modulating inflammation-related injuries.

Complement component C5 recruits neutrophils in the absence of C3 during respiratory infection with modified vaccinia virus Ankara

Efficient leukocyte migration is important for an effective host response to viral infection and the development of adaptive immunity. The poxvirus strain modified vaccinia virus Ankara (MVA), a safe and efficient viral vector, rapidly induces chemokine expression and respiratory recruitment of leukocytes, which is unique among vaccinia viruses. In addition to chemokines, the complement system contributes to the attraction and activation of different types of leukocytes. Using a murine model of intranasal infection, we show in this study that MVA-induced neutrophil recruitment depends on complement component C5. Remarkably, we find that C5 mediates neutrophil recruitment to the lung, even in the absence of the central complement component C3. Our findings argue for complement C5 activation during MVA infection of the lung via a C3-independent pathway, which enables rapid recruitment of neutrophils.

Bifunctional lipocalin ameliorates murine immune complex-induced acute lung injury

Molecules that simultaneously inhibit independent or co-dependent proinflammatory pathways may have advantages over conventional monotherapeutics. OmCI is a bifunctional protein derived from blood-feeding ticks that specifically prevents complement (C)-mediated C5 activation and also sequesters leukotriene B4 (LTB₄) within an internal binding pocket. Here, we examined the effect of LTB₄ binding on OmCI structure and function and investigated the relative importance of C-mediated C5 activation and LTB₄ in a mouse model of immune complex-induced acute lung injury (IC-ALI). We describe two crystal structures of bacterially expressed OmCI: one binding a C16 fatty acid and the other binding LTB₄ (C20). We show that the C5 and LTB₄ binding activities of the molecule are independent of each other and that OmCI is a potent inhibitor of experimental IC-ALI, equally dependent on both C5 inhibition and LTB₄ binding for full activity. The data highlight the importance of LTB₄ in IC-ALI and activation of C5 by the complement pathway C5 convertase rather than by non-C proteases. The findings suggest that dual inhibition of C5 and LTB₄ may be useful for treatment of human immune complex-dependent diseases.

Zonulin as prehaptoglobin2 regulates lung permeability and activates the complement system

Zonulin is a protein involved in the regulation of tight junctions (TJ) in epithelial or endothelial cells. Zonulin is known to affect TJ in gut epithelial cells, but little is known about its influences in other organs. Prehaptoglobin2 has been identified as zonulin and is related to serine proteases (MASPs, C1qrs) that activate the complement system. The current study focused on the role of zonulin in development of acute lung injury (ALI) in C57BL/6 male mice following intrapulmonary deposition of IgG immune complexes. A zonulin antagonist (AT-1001) and a related peptide with permeability agonist activities (AT-1002) were employed and given intratracheally or intravenously. Also, zonulin was blocked in lung with a neutralizing antibody. In a dose-dependent manner, AT-1001 or zonulin neutralizing antibody attenuated the intensity of ALI (as quantitated by albumin leak, neutrophil accumulation, and proinflammatory cytokines). A similar pattern was found using the bacterial lipopolysaccharide model of ALI. Using confocal microscopy on sections of injured lungs, staining patterns for TJ proteins were discontinuous, reduced, and fragmented. As expected, the leak of blood products into the alveolar space confirmed the passage of 3 and 20 kDa dextran, and albumin. In contrast to AT-1001, application of the zonulin agonist AT-1002 intensified ALI. Zonulin both in vitro and in vivo induced generation of complement C3a and C5a. Collectively, these data suggest that zonulin facilitates development of ALI both by enhancing albumin leak and complement activation as well as increased buildup of neutrophils and cytokines during development of ALI.

Immune complexes and late complement proteins trigger activation of Syk tyrosine kinase in human CD4(+) T cells

In systemic lupus erythematosus (SLE), the autoantibodies that form immune complexes (ICs) trigger activation of the complement system. This results in the formation of membrane attack complex (MAC) on cell membrane and the soluble terminal complement complex (TCC). Hyperactive T cell responses are hallmark of SLE pathogenesis. How complement activation influences the T cell responses in SLE is not fully understood. We observed that aggregated human γ-globulin (AHG) bound to a subset of CD4(+) T cells in peripheral blood mononuclear cells and this population increased in the SLE patients. Human naive CD4(+) T cells, when treated with purified ICs and TCC, triggered recruitment of the FcRγ chain with the membrane receptor and co-localized with phosphorylated Syk. These events were also associated with aggregation of membrane rafts. Thus, results presented suggest a role for ICs and complement in the activation of Syk in CD4(+) T cells. Thus, we propose that the shift in signalling from ζ-chain-ZAP70 to FcRγ chain-Syk observed in T cells of SLE patients is triggered by ICs and complement. These results demonstrate a link among ICs, complement activation and phosphorylation of Syk in CD4(+) T cells.

Molecular mechanisms of inflammation and tissue injury after major trauma--is complement the "bad guy"?

Trauma represents the leading cause of death among young people in industrialized countries. Recent clinical and experimental studies have brought increasing evidence for activation of the innate immune system in contributing to the pathogenesis of trauma-induced sequelae and adverse outcome. As the "first line of defense", the complement system represents a potent effector arm of innate immunity, and has been implicated in mediating the early posttraumatic inflammatory response. Despite its generic beneficial functions, including pathogen elimination and immediate response to danger signals, complement activation may exert detrimental effects after trauma, in terms of mounting an "innocent bystander" attack on host tissue. Posttraumatic ischemia/reperfusion injuries represent the classic entity of complement-mediated tissue damage, adding to the "antigenic load" by exacerbation of local and systemic inflammation and release of toxic mediators. These pathophysiological sequelae have been shown to sustain the systemic inflammatory response syndrome after major trauma, and can ultimately contribute to remote organ injury and death. Numerous experimental models have been designed in recent years with the aim of mimicking the inflammatory reaction after trauma and to allow the testing of new pharmacological approaches, including the emergent concept of site-targeted complement inhibition. The present review provides an overview on the current understanding of the cellular and molecular mechanisms of complement activation after major trauma, with an emphasis of emerging therapeutic concepts which may provide the rationale for a "bench-to-bedside" approach in the design of future pharmacological strategies.

T cell activation by terminal complex of complement and immune complexes

T cell hyperactivation and complement consumption are prominent features of the immunopathology of systemic lupus erythematosus. Although complement activation is secondary to autoantibodies that form immune complexes (ICs), the trigger for alterations in human peripheral blood T cells is poorly understood. To study the impact (on T cells) of several types of preformed ICs and terminal complement complex, also referred to as C5b-9, we incubated these immune reactants with peripheral blood naive CD4(+) T cells as well as Jurkat cells and analyzed their effects on cellular behavior. We first assembled the C5b-9 in situ on the membrane and observed its assembly primarily on a single site where it promoted aggregation of membrane rafts and recruitment of the CD3 signaling complex. However, C5b-9 alone did not initiate proliferation or commencement of downstream signaling events associated with T cell activation. When T cells were treated with ICs together with nonlytic C5b-9, changes associated with T cell activation by possible antigen engagement then occurred. T cell antigen receptor signaling proteins, including ζ-chain, ZAP-70, Syk, Src, and Lck, were phosphorylated and organized in a synapse-like structure. The cytoskeleton formed F-actin spindles and a distal pole complex, resulting in a bipolar distribution of phosphorylated ezrin-radixin-moesin and F-actin. Furthermore, ICs and nonlytic C5b-9 induced T cell proliferation and IFN-γ production. These results raise the possibility that ICs and the nonlytic C5b-9 modulate T cell-mediated responses in systemic lupus erythematosus and other related chronic inflammatory disorders.

IgG immune complex induces the recruitment of inflammatory cells into the airway and TNF-mediated late airway hyperresponsiveness via NF-κB activation in mice

BACKGROUND

Many of the inflammatory proteins that are expressed in asthmatic airways are regulated, at least partially, by nuclear factor (NF)-κB. Blockade of NF-κB activity has resulted in attenuation of the cardinal features of asthma. Thus, delineating the mechanisms involved in NF-κB activation in asthma might provide an interesting approach to improving the management of asthma. However, despite its importance, the mechanism for NF-κB activation in asthma has not yet been determined.

OBJECTIVE

To examine the role of IgE and IgG antibodies (Abs) in the activation of NF-κB in mouse lungs.

METHODS

To examine the effect of IgE, mice underwent intratracheal (i.t.) instillation of an IgE immune complex (IgE-IC) (anti-2,4-dinitrophenyl hapten (DNP) IgE + DNP-BSA or DNP-OVA) and anaphylactogenic anti-IgE (LO-ME-2). For IgG, mice underwent i.t. instillation with a complex of anti-chicken gamma globulin (CGG) IgG1 mAb + CGG. NF-κB activation was determined by gel shift assay. Small interfering RNA was used for blockade of p50 expression. The effect of tumor necrosis factor (TNF) blockade was determined using anti-TNF Ab. A previously established murine model of asthma was used to assess airway hyperresponsiveness (AHR).

RESULTS

A single i.t. instillation of either IgE-IC or LO-ME-2 failed to induce activation of NF-κB in the lungs. In contrast, single i.t. instillation of IgG-IC was capable of inducing NF-κB activation, as well as NF-κB-dependent proinflammatory molecules, such as TNF and CXC chemokines. Pretreatment of p50 small interfering RNA decreased bronchoalveolar lavage fluid levels of TNF and macrophage inflammatory protein-2 induced by IgG-IC instillation. Single i.t. instillation of IgG-IC caused the recruitment of neutrophils and macrophages into the airway and TNF-mediated late AHR, but failed to induce Th2 cell-mediated asthmatic phenotypes.

CONCLUSION

IgG, but not IgE, is the major Ab that induces not only NF-κB activation and NF-κB-dependent proinflammatory molecules in the lungs but also subsequent recruitment of inflammatory cells into the airway and TNF-mediated late AHR.

C5a receptor enables participation of mast cells in immune complex arthritis independently of Fcγ receptor modulation

OBJECTIVE

Mast cells are tissue-resident immune sentinels that are implicated in the pathogenesis of inflammatory joint disease. The aim of this study was to test our hypothesis that complement fragments could be key activators of synovial mast cells in autoimmune arthritis.

METHODS

In vivo studies used the murine K/BxN arthritis model, a distal symmetric polyarthritis mediated by IgG immune complexes. Expression of C5aR on synovial mast cells was determined by immunohistochemical and functional studies. C5aR(-/-) and control mast cells were engrafted into mast cell-deficient WBB6 F1-Kit(w) /Kit(W-v) (W/Wv) mice to examine the requirement for this receptor in arthritis. C5aR-dependent activation of mast cells was investigated in C5aR(-/-) animals and in murine and human mast cell cultures.

RESULTS

Murine synovial mast cells express functional C5aR. Unlike their wild-type counterparts, C5aR(-/-) mast cells adoptively transferred into W/Wv mice were not competent to restore arthritis, despite equivalent synovial engraftment. Activation of C5aR(-/-) mast cells by K/BxN serum in vivo remained intact, indicating that C5aR is dispensable for normal IgG-mediated triggering. Consistent with this result, cultured mast cells treated with C5a failed to modulate the expression of Fcγ receptors (FcγR) or to otherwise alter the activation threshold. In human mast cells, C5a promoted the production of the neutrophil chemotaxin interleukin-8, and recruitment of neutrophils at 24 hours after serum administration was impaired in C5aR(-/-) mice, suggesting that enhanced neutrophil chemoattractant production underlies the requirement for C5aR on mast cells in arthritis.

CONCLUSION

Stimulation via C5aR is required to unleash the proinflammatory activity of synovial mast cells in immune complex arthritis, albeit via a mechanism that is distinct from C5a-modulated expression of FcγR.

Attenuation of IgG immune complex-induced acute lung injury by silencing C5aR in lung epithelial cells

Acute lung injury (ALI) in mouse lung occurs after distal airway deposition of IgG immune complexes (IgGICs), resulting in a breakdown of the vascular-airway barrier, causing intrapulmonary edema, hemorrhage, and accumulation of neutrophils [polymorphonuclear leukocytes (PMNs)] in the alveolar compartment, these changes being complement (C5a) and C5a receptor (C5aR) dependent. In this ALI model, C5aR expression (protein) was found to occur on upper (bronchial) and lower (alveolar) airway epithelial cells. An adenovirus construct (siRNA) was used to silence mRNA for C5aR in the lung. Under such conditions, C5aR protein was markedly reduced on lung epithelial cells, resulting in much reduced leakage of albumin into the lung, diminished buildup of PMNs, and lower levels of proinflammatory mediators in bronchoalveolar lavage fluids. These studies indicate that bronchial and alveolar epithelial cell C5aR is up-regulated and greatly contributes to inflammation and injury in the lung. The use of siRNA administered into the airways avoids systemic suppression of C5aR, which might compromise innate immunity. It is possible that such an intervention might be employed in humans with ALI or acute respiratory distress syndrome as well as in upper-airway inflammatory diseases, such as chronic obstructive pulmonary disease and asthma, where there is evidence for complement activation and buildup of PMNs.

Upregulation of phagocyte-derived catecholamines augments the acute inflammatory response

Following our recent report that phagocytic cells (neutrophils, PMNs, and macrophages) are newly discovered sources of catecholamines, we now show that both epinephrine and norepinephrine directly activate NFkappaB in macrophages, causing enhanced release of proinflammatory cytokines (TNFalpha, IL-1beta, IL-6). Both adrenal-intact (AD+) and adrenalectomized (ADX) rodents were used, because ADX animals had greatly enhanced catecholamine release from phagocytes, facilitating our efforts to understand the role of catecholamines released from phagocytes. Phagocytes isolated from adrenalectomized rats displayed enhanced expression of tyrosine-hydroxylase and dopamine-beta-hydroxylase, two key enzymes for catecholamine production and exhibited higher baseline secretion of norepinephrine and epinephrine. The effects of upregulation of phagocyte-derived catecholamines were investigated in two models of acute lung injury (ALI). Increased levels of phagocyte-derived catecholamines were associated with intensification of the acute inflammatory response, as assessed by increased plasma leak of albumin, enhanced myeloperoxidase content in lungs, augmented levels of proinflammatory mediators in bronchoalveolar lavage fluids, and elevated expression of pulmonary ICAM-1 and VCAM-1. In adrenalectomized rats, development of ALI was enhanced and related to alpha(2)-adrenoceptors engagement but not to involvement of mineralocorticoid or glucocorticoid receptors. Collectively, these data demonstrate that catecholamines are potent inflammatory activators of macrophages, upregulating NFkappaB and further downstream cytokine production of these cells. In adrenalectomized animals, which have been used to further assess the role of catecholamines, there appears to be a compensatory increase in catecholamine generating enzymes and catecholamines in macrophages, resulting in amplification of the acute inflammatory response via engagement of alpha(2)-adrenoceptors.

Regulation of lung inflammation in the model of IgG immune-complex injury

Modern techniques of cell and molecular biology have rapidly uncovered the mechanisms underlying inflammatory injury of the lung. This expanding knowledge (which includes an understanding of complement, cell surface receptors, cytokines and chemokines, transcription factors, oxidants, proteinases, and endogenous inhibitors, as well as the role of leukocyte adhesion-promoting molecules) has provided new insights into the inflammatory system in general, as well as in the context of lung injury. In this review, we summarize recent progress in understanding the regulation of lung inflammation by using immunoglobulin G (IgG) immune complex-induced lung injury as a model. These studies have provided information on the role of various inflammatory mediators and their sequence of engagement. Insights into potential interventional approaches for the suppression of inflammatory processes in humans have emerged from those studies.

Role of biological modifiers regulating the immune response after trauma

Trauma induces a profound immunological dysfunction. This is characterised by an early state of hyperinflammation, followed by a phase of immunosuppression with increased susceptibility to infection and multiple organ failure. Therapeutic strategies directed at restoring immune homeostasis after traumatic injuries have largely failed in translation from "bench to bedside". The present review illustrates the role of biological modifiers of the posttraumatic immune response by portraying different modalities of therapeutic immune modulation. The emphasis is placed on anti-inflammatory (steroids) and immune-stimulatory (interferon) pharmacological strategies and modified resuscitative strategies, as well as more unconventional immunomodulatory approaches, such as immunonutrition.

Phagocyte-derived catecholamines enhance acute inflammatory injury

It is becoming increasingly clear that the autonomic nervous system and the immune system demonstrate cross-talk during inflammation by means of sympathetic and parasympathetic pathways. We investigated whether phagocytes are capable of de novo production of catecholamines, suggesting an autocrine/paracrine self-regulatory mechanism by catecholamines during inflammation, as has been described for lymphocytes. Here we show that exposure of phagocytes to lipopolysaccharide led to a release of catecholamines and an induction of catecholamine-generating and degrading enzymes, indicating the presence of the complete intracellular machinery for the generation, release and inactivation of catecholamines. To assess the importance of these findings in vivo, we chose two models of acute lung injury. Blockade of alpha2-adrenoreceptors or catecholamine-generating enzymes greatly suppressed lung inflammation, whereas the opposite was the case either for an alpha2-adrenoreceptor agonist or for inhibition of catecholamine-degrading enzymes. We were able to exclude T cells or sympathetic nerve endings as sources of the injury-modulating catecholamines. Our studies identify phagocytes as a new source of catecholamines, which enhance the inflammatory response.

Complement C5 mediates experimental tubulointerstitial fibrosis

Renal fibrosis is the final common pathway of most progressive renal diseases. C5 was recently identified as a risk factor for liver fibrosis. This study investigated the role of C5 in the development of renal tubulointerstitial fibrosis by (1) induction of renal fibrosis in wild-type and C5(-/-) mice by unilateral ureteral ligation (UUO) and (2) investigation of the effects of a C5a receptor antagonist (C5aRA) in UUO. In C5(-/-) mice, when compared with wild-type controls, markers of renal fibrosis (Sirius Red, type I collagen, fibronectin, alpha-smooth muscle actin, vimentin, and infiltrating macrophages) were significantly reduced on day 5 of UUO. On day 10, fibronectin mRNA and protein expression were still reduced in the C5(-/-) mice. Cortical mRNA of all PDGF isoforms and of TGF-beta(1) (i.e., central mediators of renal disease) were significantly reduced in C5(-/-) mice when compared with controls. Renal tubular cell expression of the C5aR was sparse in normal cortex but markedly upregulated after UUO. Treatment of wild-type UUO mice with C5aRA also led to a significant reduction of cortical Sirius Red staining, fibronectin protein expression, and PDGF-B mRNA expression on day 5. Neither genetic C5 deficiency nor C5aRA treatment caused any histologic changes in the nonobstructed kidneys. In cultured murine cortical tubular cells, C5a stimulated production of TGF-beta(1), and this was inhibited by C5aRA. Using a combined genetic and pharmacologic approach, C5, in particular C5a, is identified as a novel profibrotic factor in renal disease and as a potential new therapeutic target.

Co-expression of alpha(1,3)galactosyltransferase and Bacillus thuringiensis PIPLC enhances hyperacute rejection of tumor cells

The use of alpha(1,3)galactosyltransferase (alphaGT) as a method of inducing hyperacute rejection of tumors has been gaining interest recently. However, the approach is based in part on the sensitivity of each tumor line to the effects of complement lysis. Tumors expressing complement resistance factors such as membrane cofactor (CD46), decay accelerating factor (CD55) and protectin (CD59) have been shown to be more resistant to complement mediated lysis. Anchored to the membrane by a glycosylphosphoinositol moiety (GPI-anchored), CD55 and CD59 can be cleaved by Bacillus thuringiensis phosphatidylinositol-specific phospholipase C (PIPLC). Complement resistant A549 human lung carcinoma cells were engineered to express both the murine alphaGT gene and the B. thuringiensis PIPLC gene to alleviate complement resistance and enhance alphagal-mediated cancer killing. The PIPLC native signal sequence was replaced with the human epidermal growth factor signal sequence, EGFssPIPLC, to induce secretion from A549. Expression of EGFssPIPLC resulted in complete removal of CD55 and CD59 while sparing the non-GPI-anchored CD46. Results demonstrated that A549 cells transduced with two recombinant retroviral vectors carrying the alphaGT and EGFssPIPLC genes expressed high levels of alphagal epitope and exhibited a 5-fold increase in sensitivity to anti-alphagal mediated complement lysis.

Adenoviral-mediated overexpression of SOCS3 enhances IgG immune complex-induced acute lung injury

The lung inflammatory response caused by intratracheal deposition of IgG immune complexes (IC) includes the production of IL-6, which signals through activation of STAT transcription factors. Recently, suppressor of cytokine signaling 3 (SOCS3) has been shown to be a key negative regulator of IL-6/gp130/Jak/STAT3 signal transduction. Although SOCS3 has been implicated in several inflammatory diseases, very little is known regarding its activation and its function in the lung during acute inflammation. Our previous study showed that IL-6/STAT3 activation was triggered in lungs after intrapulmonary deposition of IgG IC in rats. In the current study, we sought to determine whether SOCS3 is playing a regulatory role in the lung inflammatory response. SOCS3 induction occurred during development of inflammation in the IgG IC model of lung injury. Overexpression of SOCS3 in lung using a recombinant adenovirus encoding murine SOCS3 resulted in substantial increases in lung vascular permeability and lung myeloperoxidase, together with enhanced levels of TNF-alpha, MIP-2, and keratinocyte-activated cytokine in bronchoalveolar lavage fluids. SOCS3 overexpression in lungs led to overproduction of bronchoalveolar lavage IL-6, but not IL-10, in this inflammatory model. We further show that activation of STAT3 was inhibited by SOCS3 overexpression as well as by anti-IL-6 treatment during IgG IC-induced lung injury, as determined by EMSA. In vitro, SOCS3 overexpression abrogated IL-6-induced activation of STAT3 in lung epithelial cells. These findings suggest SOCS3 is an important regulator of lung inflammatory injury after deposition of IgG IC.

Complement depletion enhances pulmonary inflammatory response after liver injury

Hepatic cryoablation can produce acute lung injury, with activation of nuclear factor (NF)-kappaB in the remnant liver and lungs, production of C-X-C chemokines, and neutrophil infiltration of the lungs. Activated complement stimulates NF-kappaB and cytokine secretion from Kupffer cells. The role of complement in the development of acute lung injury after cryoablation was examined using HLL transgenic mice (5'HIV-LTR-Luciferase gene; 5' HIV-LTR is an NF-kappaB-dependent promoter). Total complement depletion was achieved with preoperative administration of cobra venom factor (CVF). After hepatic cryoablation, bioluminescent NF-kappaB activity increased in the nonablated liver remnant by 4 hours in both control (119,093 +/- 22,808 net RLU/mg protein) and CVF-treated mice (117,722 +/- 14,932) from cumulative baseline (657 +/- 90, P < 0.0001). In the lung, complement-depletion induced significantly greater increases in NF-kappaB activation at both early and later times. Likewise, chemokines were higher in complement-depleted mice relative to controls (KC: 493 +/- 43 versus 269 +/- 29 pg/mg protein, P < 0.001; MIP-2: 171 +/- 29 versus 64 +/- 13 pg/mg protein, P < 0.0001). Pulmonary myeloperoxidase activity was equivalent at 24 hours, but complement-depletion caused a significantly more rapid influx of neutrophils. Complement depletion results in increased pulmonary inflammation following liver cryo injury via relative upregulation of NF-kappaB activity. Activated complement is not the initiator of the systemic inflammatory response; in fact, downstream components of the complement cascade may diminish subsequent inflammation.

Role of C5 in the development of airway inflammation, airway hyperresponsiveness, and ongoing airway response

The role of complement component C5 in asthma remains controversial. Here we examined the contribution of C5 at 3 critical checkpoints during the course of disease. Using an mAb specific for C5, we were able to evaluate the contribution of C5 during (a) the initiation of airway inflammation, (b) the maintenance of airway hyperresponsiveness (AHR), and (c) sustainment of an ongoing airway response to allergen provocation. Our results indicate that C5 is probably activated intrapulmonarily after infections or exposures to allergen and C5 inhibition has profound effects at all 3 critical checkpoints. In contrast to an earlier report, C5-deficient mice with established airway inflammation did not have elevated AHR to nonspecific stimuli. In the presence of airway inflammation, C5a serves as a direct link between the innate immune system and the development of AHR by engaging directly with its receptors expressed in airways. Through their powerful chemotactic and cell activation properties, both C5a and C5b-9 regulate the downstream inflammatory cascade, which results in a massive migration of inflammatory cells into the bronchial airway lumen and triggers the release of multiple harmful inflammatory mediators. This study suggests that targeting C5 is a potential clinical approach for treating patients with asthma.

Complement factor C5a mediates renal ischemia-reperfusion injury independent from neutrophils

The complement system has been shown to mediate renal ischemia-reperfusion (I/R) injury. However, the contribution of complement factor C5a to I/R injury, in particular in the kidney, remains to be established. In this study, we investigated the impact of blocking the C5aR pathway on the inflammatory response and on the renal function in a murine model of I/R injury. First, we analyzed C5aR expression in kidneys of healthy mice. Intriguingly, we found expression on mesangial, as well as on tubular epithelial, cells. After I/R injury, C5aR expression was up-regulated in tubular epithelial cells. In addition, mRNA levels of CXC chemokines and TNF-alpha increased significantly and kidneys were heavily infiltrated by neutrophils. Blocking the C5aR pathway by a specific C5a receptor antagonist (C5aRA) abrogated up-regulation of CXC chemokines but not of TNF-alpha and reduced neutrophil infiltration by >50%. Moreover, application of the C5aRA significantly reduced loss of renal function. This improvement of function was independent of the presence of neutrophils because neutrophil depletion by mAb NIMP-R14 did not affect the protective effect of C5aRA treatment. Furthermore, blocking of the C5aR pathway had no influence on renal apoptosis. These data provide evidence that C5a is crucially involved in the pathogenesis of renal I/R injury by modulation of neutrophil-dependent as well as neutrophil-independent pathways, which include the regulation of CXC chemokines but not TNF-alpha or apoptotic pathways.

C5a anaphylatoxin is a major regulator of activating versus inhibitory FcgammaRs in immune complex-induced lung disease

IgG Fc receptors (FcgammaRs, especially FcgammaRIII) and complement (in particular, C5a anaphylatoxin) are critical effectors of the acute inflammatory response to immune complexes (ICs). However, it is unknown whether and how these two key components can interact with each other in vivo. We use here a mouse model of the acute pulmonary IC hypersensitivity reaction to analyze their potential interaction. FcgammaRIII and C5aR are coexpressed on alveolar macrophages (AMs), and both FcgammaRIII and C5aR mutant mice display impaired immune responses. We find that recombinant human C5a (rhC5a) can control inverse expression of various FcgammaRs, and costimulation of ICs with rhC5a results in strong enhancement of FcgammaRIII-triggered cellular activation in vitro and in vivo. Moreover, we show here that early IC-induced bioactive C5a, and its interaction with C5aR, causes induction of activating FcgammaRIII and suppression of inhibitory FcgammaRII on AMs that appears crucial for efficient cytokine production and neutrophil recruitment in lung pathology. Therefore, C5a, which is a potent chemoattractant, has a broader critical function in regulating the inhibitory/activating FcgammaRII/III receptor pair to connect complement and FcgammaR effector pathways in immune inflammation.

C5a anaphylatoxin is a major regulator of activating versus inhibitory FcgammaRs in immune complex-induced lung disease

IgG Fc receptors (FcgammaRs, especially FcgammaRIII) and complement (in particular, C5a anaphylatoxin) are critical effectors of the acute inflammatory response to immune complexes (ICs). However, it is unknown whether and how these two key components can interact with each other in vivo. We use here a mouse model of the acute pulmonary IC hypersensitivity reaction to analyze their potential interaction. FcgammaRIII and C5aR are coexpressed on alveolar macrophages (AMs), and both FcgammaRIII and C5aR mutant mice display impaired immune responses. We find that recombinant human C5a (rhC5a) can control inverse expression of various FcgammaRs, and costimulation of ICs with rhC5a results in strong enhancement of FcgammaRIII-triggered cellular activation in vitro and in vivo. Moreover, we show here that early IC-induced bioactive C5a, and its interaction with C5aR, causes induction of activating FcgammaRIII and suppression of inhibitory FcgammaRII on AMs that appears crucial for efficient cytokine production and neutrophil recruitment in lung pathology. Therefore, C5a, which is a potent chemoattractant, has a broader critical function in regulating the inhibitory/activating FcgammaRII/III receptor pair to connect complement and FcgammaR effector pathways in immune inflammation.

Membrane attack complex contributes to destruction of vascular integrity in acute lung allograft rejection

The lung is known to be particularly susceptible to complement-mediated injury. Both C5a and the membrane attack complex (MAC), which is formed by the terminal components of complement (C5b-C9), can cause acute pulmonary distress in nontransplanted lungs. We used C6-deficient rats to investigate whether MAC causes injury to lung allografts. PVG.R8 lungs were transplanted orthotopically to MHC class I-incompatible PVG.1U recipients. Allografts from C6-sufficient (C6(+)) donors to C6(+) recipients were rejected with an intense vascular infiltration and diffuse alveolar hemorrhage 7 days after transplantation (n = 5). Ab and complement (C3d) deposition was accompanied by extensive vascular endothelial injury and intravascular release of von Willebrand factor. In contrast, lung allografts from C6-deficient (C6(-)) donors to C6(-) recipients survived 13-17 days (n = 5). In the absence of C6, perivascular mononuclear infiltrates of ED1(+) macrophages and CD8(+) T lymphocytes were present 7 days after transplantation, but vascular endothelial cells were quiescent, with minimal von Willebrand factor release and no evidence of alveolar hemorrhage or edema. Lung allografts were performed from C6(-) donors to C6(+) recipients (n = 5) and from C6(+) donors to C6(-) recipients (n = 5) to separate the effects of systemic and local C6 production. Lungs transplanted from C6(+) donors to C6(-) recipients had increased alveolar macrophages and capillary injury. C6 production by lung allografts was demonstrated at the mRNA and protein levels. These results demonstrate that MAC causes vascular injury in lung allografts and that the location of injury is dependent on the source of C6.

Activator protein-1 activation in acute lung injury

The role of activator protein-1 (AP-1) in inflammation is primarily unknown. AP-1 was evaluated in nuclear extracts from alveolar macrophages and whole lung nuclear extracts during acute lung injury after deposition of IgG immune complexes. AP-1 activation occurred in macrophages and in whole lung extracts, but with distinctly different time courses. Low levels of constitutive AP-1 were observed in normal rat lung as determined by the electrophoretic mobility shift assay. Increased AP-1 was detected 2 hours after initiation of the inflammatory response in lung with a further increase by 4 hours, while AP-1 activation was found in alveolar macrophages 0.5 hour after onset of the inflammatory response. mRNAs and proteins for c-fos, c-jun, jun-B, and jun-D were all up-regulated in whole lung tissues and in alveolar macrophages during acute lung injury induced by IgG immune complex deposition. Depletion of lung macrophages sharply reduced AP-1 activation, as did anti-tumor necrosis factor-alpha, whereas complement depletion showed no effect on lung AP-1 activation. The data suggest that activation of AP-1 occurs in both alveolar macrophages and in the lung, and this activation process is macrophage- and tumor necrosis factor-alpha-dependent.

Roles of the complement system in human neurodegenerative disorders: pro-inflammatory and tissue remodeling activities

Complement is an important component of the innate immune response with the capacity to recognize and clear infectious challenges that invade the CNS through a damaged blood brain barrier. For instance, the membrane attack complex is involved in cytotoxic and cytolytic activities while other smaller fragments lead to cell activation (chemotaxis) and phagocytosis of the intruders. It is noteworthy that there is a growing body of evidence that uncontrolled complement biosynthesis and activation in the CNS can contribute to exacerbate the neuronal loss in several neurodegenerative disorders. We provide here an insightful review of the double-edged sword activities of the local innate complement system in the CNS and discuss further the potential therapeutic avenues of delivering complement inhibitors to control brain inflammation.

Regulation of experimental lung inflammation

Acute lung inflammation is an important component of a number of pulmonary diseases, including acute respiratory distress syndrome (ARDS). Much has been learned about the manner in which various insults to lung, such as infection or trauma, bring about recruitment of neutrophils into alveoli and small airways, resulting in parenchymal damage and organ dysfunction. In this brief review, we discuss the endogenous mechanisms in which the lung regulates the acute inflammatory response in rats to intrapulmonary deposition of IgG immune complexes. Emphasis is given to the participation of the transcription factor, NF-kappaB, in the development of lung injury and the endogenous mediators which attempt to control the extent of lung inflammation by modulating the activation of NF-kappaB.

A role for complement C5 in organism containment and granulomatous response during murine tuberculosis

The molecular mechanisms underlying protective granuloma formation and control of bacterial growth during infection with Mycobacterium tuberculosis (MTB) are not yet completely understood. MTB-infected mice with natural deficiency in complement component C5 are unable to develop productive granulomatous responses, and are impaired in limiting organism growth within the lung. To address the molecular basis for this histologic dysfunction, congenic complement C5-sufficient (B10.D2-H2d H2-T18c Hcl/nSnJ) and complement C5-deficient strains (B10.D2-H2d H2-T18c Hco/oSnJ) congenic mice were infected with Mycobacterium tuberculosis, and cytokine and chemokine responses were examined. Twelve and 28 days after infection, lungs showed elevated messages for multiple inflammatory cytokines in both congenic strains. Interleukin (IL)-12(p40) mRNA was also induced during infection in C5-deficient mice, although levels were significantly decreased compared to C5-sufficient congenics. C5-deficient mice also demonstrated reduced KC, MIP-2, IP-10, and MCP-1 mRNA. The defect may directly involve C5-mediated effects on macrophage responses; C5-deficient bone marrow derived macrophages had significantly reduced secretion of KC, MIP-1 alpha and MIP-2 compared to C5-sufficient macrophages following in vitro infection. These findings indicate a role for C5 in mediation of chemotactic and activation events that are the basis for granulomatous responses during murine tuberculosis.

Regulatory effects of eotaxin on acute lung inflammatory injury

Eotaxin, which is a major mediator for eosinophil recruitment into lung, has regulatory effects on neutrophil-dependent acute inflammatory injury triggered by intrapulmonary deposition of IgG immune complexes in rats. In this model, eotaxin mRNA and protein were up-regulated during the inflammatory response, resulting in eotaxin protein expression in alveolar macrophages and in alveolar epithelial cells. Ab-induced blockade of eotaxin in vivo caused enhanced NF-kappaB activation in lung, substantial increases in bronchoalveolar lavage levels of macrophage inflammatory protein (MIP)-2 and cytokine-induced neutrophil chemoattractant (CINC), and increased MIP-2 and CINC mRNA expression in alveolar macrophages. In contrast, TNF-alpha levels were unaffected, and IL-10 levels fell. Under these experimental conditions, lung neutrophil accumulation was significantly increased, and vascular injury, as reflected by extravascular leak of (125)I-albumin, was enhanced. Conversely, when recombinant eotaxin was administered in the same inflammatory model of lung injury, bronchoalveolar lavage levels of MIP-2 were reduced, as was neutrophil accumulation and the intensity of lung injury. In vitro stimulation of rat alveolar macrophages with IgG immune complexes greatly increased expression of mRNA and protein for MIP-2, CINC, MIP-1alpha, MIP-1beta, TNF-alpha, and IL-1beta. In the copresence of eotaxin, the increased levels of MIP-2 and CINC mRNAs were markedly diminished, whereas MIP-1alpha, MIP-1beta, TNF-alpha, and IL-1beta expression of mRNA and protein was not affected. These data suggest that endogenous eotaxin, which is expressed during the acute lung inflammatory response, plays a regulatory role in neutrophil recruitment into lung and the ensuing inflammatory damage.

Systemic complement depletion diminishes perihematomal brain edema in rats

BACKGROUND AND PURPOSE

The complement cascade is activated after experimental intracerebral hemorrhage (ICH). It remains unclear, however, whether depleting the complement system will improve injury resulting from ICH. This study investigated the effects of systemic complement depletion on brain edema formation after ICH.

METHODS

Fifty-six pentobarbital-anesthetized Sprague-Dawley rats were used. Treatment animals were complement-depleted with cobra venom factor (CVF) (intraperitoneally). Control rats received an equal volume of saline injection (intraperitoneally). In both treatment and control rats, autologous blood (100 microL) was infused stereotaxically into the right basal ganglia. Rats were killed 2, 24, or 72 hours later for brain water, ion, and tumor necrosis factor-alpha (TNF-alpha) measurements, for Western blot analysis, and for immunohistochemical studies. Brain edema was quantitated by wet/dry weight. TNF-alpha levels were measured by enzyme-linked immunosorbent assay. Western blot analysis was applied for C9 semiquantification. Immunohistochemistry was used to detect complement C3d, C5a, C9, and myeloperoxidase.

RESULTS

Perihematomal brain edema was reduced by systemic complement depletion at 24 hours (78.8+/-0.6% versus 81.5+/-0.8% in control, P:<0.01) and 72 hours (81.5+/-1.5% versus 83.6+/-0.9% in control, P:<0.05), while cerebellar water content was unaffected (78.2+/-0.3% versus 78.0+/-0. 1%). Complement depletion reduced TNF-alpha production 2 hours after ICH. Immunocytochemistry showed that complement depletion significantly reduced perihematomal C9 deposition, C3d production, and the number of C5a- and myeloperoxidase-positive cells.

CONCLUSIONS

Complement depletion by CVF attenuates brain edema in ICH, indicating that complement activation plays an important role in ICH-induced brain edema. Preventing complement activation may be effective in the treatment of ICH.

Attenuation of experimental autoimmune demyelination in complement-deficient mice

The exact mechanisms leading to CNS inflammation and myelin destruction in multiple sclerosis and in its animal model, experimental allergic encephalomyelitis (EAE) remain equivocal. In both multiple sclerosis and EAE, complement activation is thought to play a pivotal role by recruiting inflammatory cells, increasing myelin phagocytosis by macrophages, and exerting direct cytotoxic effects through the deposition of the membrane attack complex on oligodendrocytes. Despite this assumption, attempts to evaluate complement's contribution to autoimmune demyelination in vivo have been limited by the lack of nontoxic and/or nonimmunogenic complement inhibitors. In this report, we used mice deficient in either C3 or factor B to clarify the role of the complement system in an Ab-independent model of EAE. Both types of complement-deficient mice presented with a markedly reduced disease severity. Although induction of EAE led to inflammatory changes in the meninges and perivascular spaces of both wild-type and complement-deficient animals, in both C3(-/-) and factor B(-/-) mice there was little infiltration of the parenchyma by macrophages and T cells. In addition, compared with their wild-type littermates, the CNS of both C3(-/-) and factor B(-/-) mice induced for EAE are protected from demyelination. These results suggest that complement might be a target for the therapeutic treatment of inflammatory demyelinating diseases of the CNS.

Complement components of the innate immune system in health and disease in the CNS

The innate immune system and notably the complement (C) system play important roles in host defense to recognise and kill deleterious invaders or toxic entities, but activation at inappropriate sites or to an excessive degree can cause severe tissue damage. C has been implicated as a factor in the exacerbation and propagation of tissue injury in numerous diseases including neurodegenerative disorders. In this article, we review the evidence indicating that brain cells can synthesise a full lytic C system and also express specific C inhibitors (to protect from C activation and C lysis) and C receptors (involved in cell activation, chemotaxis and phagocytosis). We also summarise the mechanisms involved in the antibody-independent activation of the classical pathway of C in Alzheimer's disease, Huntington's disease and Pick's disease. Although the primary role of C activation on a target cell is to induce cell lysis (particularly of neurons), we present evidence indicating that C (C3a, C5a, sublytic level of C5b-9) may also be involved in pro- as well as anti-inflammatory activities. Moreover, we discuss evidence suggesting that local C activation may contribute to tissue remodelling activities during repair in the CNS.

Interleukin-10 inhibits pulmonary NF-kappaB activation and lung injury induced by hepatic ischemia-reperfusion

Hepatic ischemia and reperfusion cause local and remote organ injury. This injury culminates from an integrated cascade of proinflammatory cytokines, chemokines, and adhesion molecules, many of which are regulated by the transcription factor nuclear factor-kappaB (NF-kappaB). The anti-inflammatory cytokine interleukin-10 (IL-10) has been shown to have inhibitory effects on NF-kappaB. The objective of the current study was to determine whether IL-10 could suppress pulmonary NF-kappaB activation and ensuing lung injury induced by hepatic ischemia-reperfusion. C57BL/6 mice underwent partial hepatic ischemia with or without intravenous administration of IL-10. Hepatic ischemia-reperfusion resulted in pulmonary NF-kappaB activation, increased mRNA expression of tumor necrosis factor-alpha (TNF-alpha), and macrophage inflammatory protein-2 (MIP-2), as well as increased pulmonary neutrophil accumulation and lung edema. Administration of IL-10 suppressed lung NF-kappaB activation, reduced TNF-alpha and MIP-2 mRNA expression, and decreased pulmonary neutrophil recruitment and lung injury. The data suggest that IL-10 protects against hepatic ischemia and reperfusion-induced lung injury by inhibiting lung NF-kappaB activation and the resulting pulmonary production of proinflammatory mediators.