CMA1 and idiopathic pulmonary fibrosis: Several studies have reported that mast cells and fibroblasts colocalize in the lung [14,15,16,22], where mast cell granules containing merely tryptase and not chymase are described to be the dominating mast cell type in the alveolar regions [15], and that mast cells are located close to fibrotic foci and alveolar type II cells in lung tissue samples from IPF patients [22].