IMMUNOLOCALIZATION OF CATHEPSIN-D IN PNEUMOCYTES OF NORMAL HUMAN LUNGAND IN PULMONARY FIBROSIS

Cathepsin D expression has been assessed by immunohistochemistry and i mmunoelectron microscopy in fetal, normal adult and injured lungs of h uman beings. In addition to the well known positivity of alveolar macr ophages and the bronchial epithelial cells, normal type I and to a les ser extent type II pneumocytes showed a granular, cytoplasmic staining pattern. Using immunogold labelling of lowicryl embedded human lung, cathepsin D was present in lysosomes of epithelial cells. Double immun ofluorescence labelling employing type I and type II specific antibodi es or lectins confirmed the epithelial staining for cathepsin D. At th e terminal sac period during lung development cathepsin D appears in t he alveolar epithelium, In fibrotic specimens, enhanced immunoreactivi ty was found in epithelial and non-epithelial cells. Proliferative epi thelial formations were strongly stained with cathepsin D antibodies, whereas detached, desquamated epithelial cells were weakly positive or negative. We suggest that cathepsin D plays a role in the remodelling process during fibrogenesis.