Abstract
Hypersensitivity pneumonitis (HP) typically presents with interstitial inflammation and granulomas induced by an aberrant immune response to inhaled Ags in sensitized individuals. Although IL-17A is involved in the development of HP, the cellular sources of IL-17A and the mechanisms by which IL-17A contributes to granuloma formation remain unclear. Recent studies report that γδ T cells produce IL-17A and exhibit memory properties in various diseases. Therefore, we focused on IL-17A-secreting memory γδ T cells in the sensitization phase and aimed to elucidate the mechanisms by which IL-17A contributes to granuloma formation in HP. We induced a mouse model of HP using pigeon dropping extract (PDE) in wild-type and IL-17A knockout (IL-17A-/-) mice. IL-17A-/- mice exhibited reduced granulomatous areas, attenuated aggregation of CD11b+ alveolar macrophages, and reduced levels of CCL2, CCL4, and CCL5 in the bronchoalveolar lavage fluid. Among IL-17A+ cells, more γδ T cells than CD4+ cells were detected after intranasal PDE administration. Interestingly, the expansion of IL-17A-secreting Vγ4+ or Vγ1-Vγ4- cells of convalescent mice was enhanced in response to the sensitizing Ag. Additionally, coculture of macrophages with PDE and Vγ4+ cells purified from PDE-exposed convalescent mice produced significantly more IL-17A than coculture with Vγ4+ cells from naive mice. Our findings demonstrate that in the sensitization phase of HP, IL-17A-secreting memory γδ T cells play a pivotal role. Furthermore, we characterized the IL-17A/CCL2, CCL4, CCL5/CD11b+ alveolar macrophage axis, which underlies granuloma formation in HP. These findings may lead to new clinical examinations or therapeutic targets for HP.
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