IgG hexamers initiate complement-dependent acute lung injury
Simon J. Cleary, … , James C. Zimring, Mark R. Looney
Simon J. Cleary, … , James C. Zimring, Mark R. Looney
Published March 26, 2024
Citation Information: J Clin Invest. 2024;134(11):e178351. https://doi.org/10.1172/JCI178351.
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Research Article Pulmonology

IgG hexamers initiate complement-dependent acute lung injury

Abstract

Antibodies can initiate lung injury in a variety of disease states such as autoimmunity, in reactions to transfusions, or after organ transplantation, but the key factors determining in vivo pathogenicity of injury-inducing antibodies are unclear. Harmful antibodies often activate the complement cascade. A model for how IgG antibodies trigger complement activation involves interactions between IgG Fc domains driving the assembly of IgG hexamer structures that activate C1 complexes. The importance of IgG hexamers in initiating injury responses was not clear, so we tested their relevance in a mouse model of alloantibody- and complement-mediated acute lung injury. We used 3 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 an 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.

Authors

Simon J. Cleary, Yurim Seo, Jennifer J. Tian, Nicholas Kwaan, David P. Bulkley, Arthur E.H. Bentlage, Gestur Vidarsson, Éric Boilard, Rolf Spirig, James C. Zimring, Mark R. Looney

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Figure 5

Treatment with recombinant Fc hexamer decoys prevents alloantibody-mediated acute lung injury.

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Treatment with recombinant Fc hexamer decoys prevents alloantibody-media...
(A) Molecular representation of CSL777, an investigational recombinant Fc hexamer decoy treatment that inhibits classical complement activation, based on PDB entry 7X13 (52). (B) Molecular representation of SCIg, a pooled hIg therapeutic with antiinflammatory properties at high doses, based on PDB entry 1HZH. Scale bar: 5 nm. (C) Lung vascular permeability and (D) excess lung water measurements from LPS-primed BALB/c mice given i.p. vehicle or CSL777 at the indicated doses 1 hour before i.v. injection of 34-1-2S or mIgG2a isotype control. (E) Lung vascular permeability and (F) excess lung water measurements from LPS-primed BALB/c mice given i.p. vehicle or 2,000 mg/kg SCIg 1 hour before i.v. injection of 34-1-2S or mIgG2a isotype control. (G and H) Immunofluorescence showing pulmonary arterioles stained for complement C4/C4b/C4d (red) and Acta2 (cyan) in lung sections from LPS-primed BALB/c mice given the indicated treatments, representative of 3 samples per group fixed 5 minutes after antibody injections. White arrowheads point to arterioles with endothelial positivity for C4/C4b/C4d. Scale bars: 50 μm. Graphs show the mean ± SEM, with the horizontal line representing 95% CIs of data from no-injury controls (from vehicle plus isotype control group). *P < 0.05, **P < 0.01 and ***P < 0.0001; log10-transformed data were analyzed using either (C and D) an ordinary 1-way ANOVA (C and D), Dunnett’s multiple-comparison test for differences relative to the vehicle plus 34-1-2S group (C and D), or 2-tailed, unpaired t test (E and F). n = 10/group.