Transcriptional analysis of TREM-1+ and TREM-1- airway eosinophils during allergic inflammation

Triggering Receptor Expressed on Myeloid cells 1 (TREM-1) an innate receptor that canonically amplifies inflammatory signaling in neutrophils and monocytes, plays a central role in regulating lung inflammation. Utilizing a murine model of asthma, flow cytometry revealed TREM-1+ eosinophils in the lung tissue and airway during allergic airway inflammation. TREM-1 expression was restricted to recruited, inflammatory eosinophils. Expression was induced on bone marrow derived eosinophils by incubation with IL-33, LPS, or GM-CSF. Compared to TREM-1- airway eosinophils, TREM-1+ eosinophils were enriched for pro-inflammatory gene sets including migration, respiratory burst, and cytokine production. Unexpectedly, eosinophil-specific ablation of TREM-1 increased airway IL-5 and lung tissue eosinophil accumulation. Further investigation of transcriptional data revealed apoptosis related gene sets were enriched in TREM-1+ eosinophils. Annexin V staining demonstrated higher rates of apoptosis among TREM-1+ eosinophils compared to TREM-1- eosinophils in the inflammatory airway. In vitro, Trem1/3-/- eosinophils were protected from apoptosis. Finally, inhibition of reactive oxygen species production with diphenyleneiodonium protected WT bone marrow derived eosinophils from apoptosis more than Trem1/3-/- eosinophils, suggesting that superoxide accounted for more apoptosis in WT cells. These data demonstrate protein level expression of TREM-1 by eosinophils for the first time, define a population of TREM-1+ inflammatory eosinophils, and reveal that eosinophil TREM-1 restricts key features of type 2 lung inflammation. Paired eosinophil (SSChi CD45+ CD11b+ CD11clo/mid Ly6Glo/mid Siglec-F+) samples were collected from pooled lung lavage WT mice treated to induce allergic airway inflammation . Two samples were sorted from each lavage samples: TREM-1+ denoted by "T" and TREM-1- denoted by "N". Each sample includes a source number ie "101" and TREM status ie "T" which combined would be "101T."