High-dimensional analysis reveals a pathogenic role of inflammatory monocytes in experimental diffuse alveolar hemorrhage

Diffuse alveolar hemorrhage (DAH) is a life-threatening pulmonary complication associated with systemic lupus erythematous and other autoimmune diseases. Little is known about the pathophysiology of DAH and no targeted therapy is currently available. Pristane treatment in mice induces systemic autoimmunity and lung hemorrhage that recapitulates hallmark pathologic features of human DAH. Using this experimental model, we performed high dimensional analysis of lung immune cells in DAH by mass cytometry and single cell RNA sequencing. We found a large influx of myeloid cells to the lungs in DAH and defined the gene expression profile of infiltrating monocytes. Using three models of monocyte deficiency and complementary transfer studies, we established a central role of inflammatory monocytes in the development of DAH. We further found that the myeloid transcription factor interferon regulatory factor 8 (Irf8) is essential to the development of both DAH and type-I interferon-dependent autoimmunity. These findings collectively reveal monocytes as a potential treatment target in DAH. Examination of gene expression in peritoneal cells from 1) wild-type mice treated with PBS, 2) wild-type mice treatd with pristane, and 3) Irf8-deficient mice treated with pristane