Cldn10-positive cells found in the airspace of IPF lungs did not show Cldn10 expression at their cell-cell contact sites including tight junctions (Figure 4B, D & E) whereas they displayed slight traces of ultrastructural features of mature club cells, e.g. cytoplasmic granules (area circled by dot-dashed line in Figure 4D) and well-developed endoplasmic reticulum (Figure 4F). This evidence concerns the gene CLDN10 and idiopathic pulmonary fibrosis.