Immunophenotyping of Acute Inflammatory Exacerbations of Lung Injury Driven by Mutant Surfactant Protein-C: A Role for Inflammatory Eosinophils

Acute inflammatory exacerbations (AIEs) represent immune-driven deteriorations of many chronic lung conditions, including COPD, asthma, and pulmonary fibrosis (PF). The first line of therapy is represented by broad-spectrum immunomodulation. Among the several inflammatory populations mobilizing during AIEs, eosinophils have been identified as promising indicators of an active inflammatory exacerbation. To better study the eosinophil-parenchymal crosstalk during AIE-PF, this work leverages a clinically relevant model of inflammatory exacerbations triggered by inducible expression of a mutation in the alveolar epithelial type 2 cell Surfactant Protein-C gene [SP-C-I73T]. Unbiased single-cell sequencing analysis of controls and SP-C-I73T mutants at a time coordinated with peak eosinophilia (14 days) defined heightened inflammatory activation, chemotaxis, and survival signaling (IL-6, IL-4/13, STAT3, Glucocorticoid Receptor, mTOR, and MYC) in eosinophils. To study the impact of eosinophils in inflammatory exacerbations, the SP-C-I73T line was crossed with eosinophil lineage deficient mice (GATA1(Delta dbl)) to produce the SP-C(I73T)GATA1(KO) line. Time course analysis (7-42 days) demonstrated improved lung histology, survival, and reduced inflammation in SP-C(I73T)GATA1(KO) cohorts. Spectral flow cytometry of tissue digests confirmed eosinophil depletion in GATA1(KO) mice and the absence of a compensatory shift in neutrophils and immature monocyte recruitment. Eosinophil deletion resulted in progressive monocyte-derived macrophage accumulation (14 days post-injury), combined with declines in CD3(+)CD4(+) lymphocyte and B220(+) B cell abundance. Histochemical analysis revealed atypical inflammatory cell activation in SP-C(I73T)GATA1(KO) mice, with reduced numbers of Arg-1(+) and iNOS(+) cells, but increases in tgfb1 mRNA expression in bronchoalveolar lavage cells and tissue. Dexamethasone treatment (1 mg/kg daily, i.p.) was utilized to investigate corticosteroid efficacy in highly eosinophilic exacerbations induced by mutant SP-C-I73T. Dexamethasone successfully reduced total and eosinophil (CD11b(+)SigF(+)CD11c(-)) counts at 14 days and was linked to reduced evidence of structural damage and perivascular infiltrate. Together, these results illustrate the deleterious role of eosinophils in inflammatory events preceding lung fibrosis and demonstrate the efficacy of corticosteroid treatment in highly eosinophilic exacerbations induced by mutant SP-C-I73T.