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IgG hexamers initiate acute lung injury.

ABSTRACT: Antibodies can initiate lung injury in a variety of disease states such as autoimmunity, transfusion reactions, or after organ transplantation, but the key factors determining in vivo pathogenicity of injury-inducing antibodies are unclear. A previously overlooked step in complement activation by IgG antibodies has been elucidated involving interactions between IgG Fc domains that enable assembly of IgG hexamers, which can optimally activate the complement cascade. Here, we tested the in vivo relevance of IgG hexamers in a complement-dependent alloantibody model of acute lung injury. We used three approaches to block alloantibody hexamerization (antibody carbamylation, the K439E Fc mutation, or treatment with domain B from Staphylococcal protein A), all of which reduced acute lung injury. Conversely, Fc mutations promoting spontaneous hexamerization made a harmful alloantibody into a more potent inducer of acute lung injury and rendered an innocuous alloantibody pathogenic. Treatment with a recombinant Fc hexamer 'decoy' therapeutic protected mice from lung injury, including in a model with transgenic human FCGR2A expression that exacerbated pathology. These results indicate a direct in vivo role of IgG hexamerization in initiating acute lung injury and the potential for therapeutics that inhibit or mimic hexamerization to treat antibody-mediated diseases.

SUBMITTER: Cleary SJ

PROVIDER: S-EPMC10849723 | biostudies-literature | 2024 Jan

REPOSITORIES: biostudies-literature

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IgG hexamers initiate acute lung injury.

Cleary Simon J SJ Seo Yurim Y Tian Jennifer J JJ Kwaan Nicholas N Bulkley David P DP Bentlage Arthur E H AEH Vidarsson Gestur G Boilard Éric É Spirig Rolf R Zimring James C JC Looney Mark R MR

bioRxiv : the preprint server for biology 20240127

Antibodies can initiate lung injury in a variety of disease states such as autoimmunity, transfusion reactions, or after organ transplantation, but the key factors determining in vivo pathogenicity of injury-inducing antibodies are unclear. A previously overlooked step in complement activation by IgG antibodies has been elucidated involving interactions between IgG Fc domains that enable assembly of IgG hexamers, which can optimally activate the complement cascade. Here, we tested the in vivo re ...[more]

PMID: 38328049

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Project description:BackgroundThe 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.ObjectivesThe 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.SettingDepartment of Pathogenic Biology and Immunology, Medical School of Southeast University.SubjectsMice with down-regulated/up-regulated PPARγ activity or down-regulation of Early growth response protein 1 (Egr-1) expression, and the corresponding controls.InterventionsAcute 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 resultsWe 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.ConclusionDuring 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.

Project description:With advances in supportive therapy in the last two decades, mortality rates from ALI/ARDS have improved somewhat, but remain around 30 to 40% with significant morbidity in survivors. Several promising treatments are in various stages of evaluation, but many have failed to prove beneficial in large randomized clinical trials (RCT). The first definitive step forward in ALI therapeutics occurred recently as a result of a large RCT demonstrating a mortality decrease from 40 to 31% with the use of low-volume ventilation strategies. From this, it is clear that the opportunity for successful intervention in ALI exists. However, therapeutic advances remain frustrated by the lack of complete understanding of ALI pathophysiology. This stresses the importance of integrating basic and clinical research of the molecular pathogenesis of this disease. The conclusions of a recent National Heart, Lung, and Blood Institute (NHLBI) Working Group on ALI support this type of research as a priority for future investigations of ALI. One of the areas of research given priority by this ALI Working Group is the issue of ALI severity progression and the role of cells of innate immunity in this process. Currently, the processes that determine which ALI patients progress to ARDS and which do not are unclear. As with many phenotype differences, there is most likely a genetic component involved. The basis for this has been demonstrated. For example, a surfactant protein B (SP-B) polymorphism appears to increase a patient’s risk of developing ALI from pneumonia. Additionally, a polymorphism in the promoter region of the gene for interleukin-6 (IL-6) has been associated with a poor prognosis in patients with ARDS. Understanding the intracellular processes of these genes and the cells expressing them in ALI progression could lead to the identification of molecular markers of ALI severity and eventually to the development of targeted therapies. An examination of genetically uniform animals will provide a clearer insight into the interaction between immune cells in ALI progression as well as guide future human experiments. Keywords: Time Series Design, ALI - acute lung injury, ARDS - acute respiratory distress syndrome, CLP - cecal ligation and puncture

Project description:Although respiratory distress is a common complication of severe malaria, little is known about the underlying molecular basis of lung dysfunction. Animal models have provided powerful insights into the pathogenesis of severe malaria syndromes such as cerebral malaria; however, no model of malaria-induced lung injury has been definitively established. This work used bronchoalveolar lavage (BAL), histopathology and gene expression analysis to examine the development of acute lung injury (ALI) in mice infected with Plasmodium berghei ANKA (PbA). BAL fluid of PbA-infected C57BL/6 mice revealed a significant increase in IgM and total protein prior to the development of cerebral malaria (CM), indicating disruption of the alveolar-capillary membrane barrier â the physiological hallmark of acute lung injury (ALI). In contrast to sepsis-induced ALI, BAL fluid cell counts remained constant with no infiltration of neutrophils. Histopathology showed septal inflammation without cellular transmigration into the alveolar spaces. Microarray analysis comparing malaria-induced ALI with sepsis-induced ALI identified several common gene ontology groups characterizing ALI in these models, including defense and immune response. Severity of malaria-induced ALI varied in a panel of inbred mouse strains, and development of ALI correlated with peripheral parasite burden but not CM susceptibility. CD36-/- mice, which have decreased parasite lung sequestration, were relatively protected from ALI. In summary, parasite burden and CD36-mediated sequestration in the lung are primary determinants of ALI in experimental murine malaria. Furthermore, differential susceptibility of mouse strains to malaria-induced ALI and CM indicate that distinct genetic determinants likely regulate susceptibility to these two important causes of malaria-associated morbidity and mortality. Keywords: Time course Lungs were excised immediately following euthanasia, snap-frozen in liquid nitrogen and stored at â80Â°C until use. Total RNA was extracted using Trizol reagent (Invitrogen) according to the manufacturerâs instructions, and mRNA was purified using an Oligo-dT cellulose column (NEB, Mississauga, ON) as described previously [54]. cDNA with incorporated 5-(3-aminoallyl)-2âdeoxyuridine-5â-triphosphate (AAdUTP; Sigma, Oakville ON) was reverse-transcribed from 1-2 Âµg mRNA. Purified cDNA was coupled with N-hydroxysuccinimide esters of Cy3 or Cy5 (GE Lifesciences, Baie d'Urfe QC). Cy3 and Cy5-labeled cDNA pairs and Agilent control spots were added to a final volume of 0.5ml hybridization buffer (1 M NaCl, 0.5% sodium sarcosine, 50 mM methyl ethane sulfonate (MES), pH 6.5, 33% formamide and 40Âµg salmon sperm DNA (Invitrogen)). Hybridizations were performed in Agilent hybridization (Agilent, Palo Alto CA) chambers at 42Â°C with rotation for 18-24 hours. Slides were washed in 6X SSPE, 0.005% sarcosine, followed by 0.06X SSPE, allowed to dry and scanned with a 4000A microarray scanner (Axon Instruments, Union City CA). TIFF images were quantified with GenePix (Axon Instruments). Variance stabilizing normalization [55] and loess smoothing were applied in Bioconductor [56] and the data were transformed to log2 scale. Each array was hybridized with cDNA transcribed from an RNA pool of 5 C57BL/6 mice per timepoint (Day 0 and 6) and technical replicates (dye-swap) experiments were performed for both time points.

Project description:BackgroundAcute lung injury (ALI) and its more severe form, acute respiratory distress syndrome (ARDS) are life threatening pulmonary diseases, and we are now lack of effective therapeutic methods. Inflammatory responses are essential for initiating ALI/ARDS. Thus, ameliorating inflammatory reaction might be beneficial for treatment of the disease. There are increasing data that phosphodiesterase-4 (PDE4)-selective inhibitors, which may elevate cellular cyclic adenosine 3', 5'-monophosphate (cAMP) level, could suppress inflammation. However, whether they could be used to treat IgG immune complex (IgG-IC)-associated ALI has not been determined.MethodsALI is induced by treating mice with airway deposition of IgG immune complexes. Cellular cAMP concentrations are elevated by treating mice or macrophages with Rolipram/Roflumilast. The degree of pulmonary injury is reflected by lung permeability, leukocyte accumulation, histological change and expressions of pro-inflammatory mediators. 6-Bnz-cAMP and H-89 are used to regulate protein kinase A (PKA) activity, and 8-pCPT-2'-O-Me-cAMP is applied to activate exchange proteins directly activated by cAMP (Epac). Gene expressions are analyzed by real-time PCR, ELISA or Western blot. CCAAT/enhancer binding protein (C/EBP) and activation protein 1 (AP-1) transcription activities are estimated by measuring the luciferase productions.ResultsIgG-IC-induced ALI is attenuated by the PDE4-selective inhibitor, which is due to reduced expressions of cytokine and chemokines. Interestingly, we find that cAMP downstream effector molecule PKA but not Epac is involved in negative regulation of IgG-IC-mediated pro-inflammatory mediators' productions. Mechanistically, activation of cAMP-PKA signal axis leads to inactivation of MAPK pathway, resulting in a decrease in C/EBP- and AP-1-mediated transcriptions of pro-inflammatory mediators.ConclusionsOur data demonstrate, for the first time, that cAMP-PKA signal is involved in down-regulation of IgG-IC-associated inflammatory responses via down-regulating MAPK activation, which is critical for transcriptional activities of C/EBP and AP-1. Collectively, our experiments provide theoretical base for the potential application of PDE4-selective inhibitor to clinic for treatment of IgG-IC-related acute lung injury.

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IgG hexamers initiate acute lung injury.

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IgG hexamers initiate acute lung injury.

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