Primary lung fibroblasts respond to IL-33, IL-13, and IL-17A by secreting factors that activate macrophages

There is mounting evidence that macrophage-fibroblast communication is key to the understanding of disease processes. To gain insights into these relationships in the context of progressive lung damage, we measured changes in protein and RNA expression of pulmonary macrophages and fibroblasts upon exposure to IL-33, IL-13, and IL-17A, which are three cytokines often implicated in pathways driving chronic lung remodeling and severe disease like emphysema. Applying an in vitro culture system, bulk-RNA sequencing, and protein assays, it was determined that IL-33, IL-13, and IL-17A used alone or in combination activated mouse alveolar macrophages to a modest extent with IL-13 inducing the most vigorous response. While lung fibroblasts also responded modestly to single and paired treatments with IL-33, IL-13, and IL-17A, simultaneous exposure to all three cytokines induced significant activation that was characterized by expression of genes associated with immune cell trafficking and activation, tissue remodeling, and maintenance of the extracellular matrix. Importantly, factors secreted by triple-treated lung fibroblasts resulted in the activation of macrophages in vitro. In addition to being the first report describing the cooperative interactions of IL-33, IL-13, and IL-17A on lung fibroblasts, these findings provide additional evidence that fibroblast-macrophage communication is a key component to repair and remodeling in the lung, as well as mechanisms that drive progression of emphysema.