IgG hexamers initiate complement-dependent acute lung injury
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
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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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 3

Inhibiting IgG hexamer assembly reduces 34-1-2S-induced acute lung injury responses.

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Inhibiting IgG hexamer assembly reduces 34-1-2S-induced acute lung injur...
(A) Molecular models of IgG hexamers based on the PDB entry 1HZH, showing Fc-Fc and Fc-C1q interaction sites. Scale bar: 5 nm. (B) Molecular model showing lysine residues in mouse IgG2a (mIgG2a), per PDB entry 1IGT. (C) Lung vascular permeability, (D) excess lung water measurements, and (E) lung complement C3 and mIgG immunostains from LPS-primed BALB/c mice after i.v. injection of carbamylated or control 34-1-2S. (F) Molecular model showing the location of Fc domain lysine 439 (K439) in hIgG1, per PDB entry 1HZH. (G) Lung vascular permeability, (H) excess lung water measurements, and (I) lung complement C4/C4b/C4d and Acta2 immunostains from LPS-primed B6.H2d mice after i.v. injection with hIgG1-34-1-2S or hIgG1-34-1-2S with the K439E mutation.(J) Molecular model showing the binding site of SpA-B to the Fc domain of hIgG1, per the PDB entries 1HZH and 5U4Y. (K) Lung vascular permeability, (L) excess lung water measurements, and (M) lung complement C4/C4b/C4d and Acta2 immunostains from LPS-primed B6.H2d mice after i.v. injection with hIgG1-34-1-2S and 75 μg SpA-B or vehicle control. Samples for the injury measurements were collected 2 hours after antibody injections, and lungs were fixed for immunostaining 5 minutes after antibody injections. Graphs show the mean ± SEM, with horizontal gray lines showing 95% CIs of measurements from no-injury control mice given LPS and nonreactive isotype antibodies. **P < 0.01 and ***P < 0.0001, by unpaired, 2-tailed t tests on log10-transformed data, with n = 8/group (C and D) and n = 12/group (G, H, K, and L), or are representative of 3 samples/group (E, I, and M). Scale bars: 50 μm (E, I, and M).