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.
View: Text | PDF
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

×

Figure 4

Fc mutations promoting IgG hexamer assembly increase the in vivo pathogenicity of alloantibodies.

Options: View larger image (or click on image) Download as PowerPoint
Fc mutations promoting IgG hexamer assembly increase the in vivo pathoge...
(A) Molecular model showing amino acids mutated in RGY-hIgG1 antibodies, per PDB entry 1HZH. (B) Negative stain electron micrographs showing single hIgG1-34-1-2S molecules and spontaneous solution-phase hexamers formed by RGY-hIgG1-34-1-2S (colored overlay highlights structures in expanded images). Numbers 1–6 label individual IgG molecules forming a hexamer. Scale bars: 10 nm (including enlarged insets). (C) Lung vascular permeability and (D) excess lung water measurements from LPS-primed B6.H2d mice injected with control or RGY-mutated hIgG1-34-1-2S mAbs at i.v. doses of either 0.3 or 1 mg/kg. (E) Immunofluorescence staining showing pulmonary arterioles stained for complement C4/C4b/C4d (red) and Acta2 (cyan) in lung sections from LPS-primed B6.H2d mice given the indicated treatments, representative of 3 samples per group fixed 5 minutes after antibody injections. Scale bars: 50 μm. (F) Lung vascular permeability and (G) excess lung water measurements from LPS-primed B6.H2d mice injected with control or RGY-mutated hIgG1-Kd1 (a novel mAb targeting only the H-2Kd MHC class I antigen) at 1 mg/kg i.v. Graphs show the mean ± SEM, with the horizontal line representing 95% CIs from no-injury controls (LPS-primed B6.H2d mice given hIgG1 isotype control i.v.). *P < 0.05, **P < 0.01 and ***P < 0.0001; log10-transformed data were analyzed using an ordinary 2-way ANOVA with Šídák’s multiple-comparison test for the effect of the Fc mutation within the dose level (C and D) or unpaired, 2-tailed t test (F and G). n = 12/group.