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The immunologic mechanisms promoting eosinophilic granulomatosis with polyangiitis (EGPA) are unclear. To characterize the mechanisms underlying pulmonary EGPA, we examined and compared EGPA paraffin-embedded lung biopsies with normal lung biopsies, using immunostaining, RNA sequencing, and RT-PCR. The results revealed novel type 2 as well as immuneregulatory features. These features included basophils and increased mast cell contents; increased immunostaining for tumor necrosis factor ligand superfamily member 14; sparse mast cell degranulation; numerous forkhead box protein P3 (FoxP3)+ regulatory T cells and IgG4 plasma cells; and abundant arachidonate 15-lipoxygenase and 25-hydroxyvitamin D-1 α hydroxylase, mitochondrial. Significantly decreased 15-hydroxyprostaglandin dehydrogenase [NAD(+)], which degrades eicosanoids, was observed in EGPA samples. In addition, there was significantly increased mRNA for chemokine (C-C motif) ligands 18 and 13 and major collagen genes, IgG4-rich immune complexes coating alveolar macrophages, and increased immunostaining for phosphorylated mothers against decapentaplegic homolog 2/SMAD2, suggesting transforming growth factor-β activation. These findings suggest a novel self-promoting mechanism of activation of alveolar macrophages by arachidonate 15-lipoxygenase-derived eicosanoids to express chemokines that recruit a combined type 2/immunoregulatory immune response, which produces these eicosanoids. These results suggest that the pulmonary EGPA immune response resembles the immune response to a tissue-invasive parasite infection. Copyright © 2020 American Society for Investigative Pathology. Published by Elsevier Inc. All rights reserved.

Citation

Zachary M Dong, Edwin Lin, Michael E Wechsler, Peter F Weller, Amy D Klion, Bruce S Bochner, Don A Delker, Mark W Hazel, Keke Fairfax, Paneez Khoury, Praveen Akuthota, Peter A Merkel, Anne-Marie Dyer, Carol Langford, Ulrich Specks, Gerald J Gleich, Vernon M Chinchilli, Benjamin Raby, Mark Yandell, Frederic Clayton. Pulmonary Eosinophilic Granulomatosis with Polyangiitis Has IgG4 Plasma Cells and Immunoregulatory Features. The American journal of pathology. 2020 Jul;190(7):1438-1448

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PMID: 32251643

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