Although we cannot make definitive conclusions in the absence of cell-type specific markers, the spindle-like morphology of some IL-33 positive cells, our IL-33 gene and protein data in IPF HLFs and the reported expression of IL-33 by freshly isolated [35] and cultured [14] IPF fibroblasts, collectively suggest that a proportion of the IL-33 positive cells in our ILD lung sections were fibroblasts. The gene discussed is IL33; the disease is idiopathic pulmonary fibrosis.