Bulkley, D. P. | bioRxiv Science

bioRxiv2024

IgG hexamers initiate acute lung injury

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. Brief summaryIgG antibodies can form hexamers. This study shows that hexamer assembly is an important event determining the ability of IgG to trigger acute lung injury. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=141 SRC="FIGDIR/small/577129v1_ufig1.gif" ALT="Figure 1"> View larger version (59K): org.highwire.dtl.DTLVardef@15b0346org.highwire.dtl.DTLVardef@33f39eorg.highwire.dtl.DTLVardef@bf0f4dorg.highwire.dtl.DTLVardef@185b5bf_HPS_FORMAT_FIGEXP M_FIG C_FIG

immunology↗

bioRxiv2018

Structural basis for cholesterol transport-like activity of the Hedgehog receptor Patched

Hedgehog protein signals mediate tissue patterning and maintenance via binding to and inactivation of their common receptor Patched, a twelve-transmembrane protein that otherwise would suppress activity of the seven-transmembrane protein, Smoothened. Loss of Patched function, the most common cause of basal cell carcinoma, permits unregulated activation of Smoothened and of the Hedgehog pathway. A cryo-EM structure of the Patched protein reveals striking transmembrane domain similarities to prokaryotic RND transporters. The extracellular domain mediates association of Patched monomers in an unusual dimeric architecture that implies curvature in the associated membrane. A central conduit with cholesterol-like contents courses through the extracellular domain and resembles that used by other RND proteins to transport substrates, suggesting Patched activity in cholesterol transport. Patched expression indeed reduces cholesterol activity in the inner leaflet of the plasma membrane, in a manner antagonized by Hedgehog stimulation and with implications for regulation of Smoothened.

biophysics↗