HETEROGENEITY IN THE IMMUNOLOCALIZATION OF CYTOKERATIN-SPECIFIC MONOCLONAL-ANTIBODIES IN THE RAT LUNG - EVALUATION OF 3 DIFFERENT ALVEOLAR EPITHELIAL-CELL TYPES

The distribution of individual cytokeratin polypeptides in the adult r at lung parenchyma was investigated by immunohistochemistry with 44 mo noclonal and 2 polyclonal antibodies. Simple epithelial cytokeratins 7 , 8, 18 and 19 were found to be expressed differently in alveolar and bronchial epithelial cells. Three distinct types of alveolar cells wer e detected according to their pattern of immunoreactivity: type II cel ls strongly expressing cytokeratins 8 and 18 and weakly expressing cyt okeratins 7 and 19 in the cell periphery; type I cells predominantly p ositive for cytokeratins 7 and 19 and weakly for cytokeratin 8; and a newly defined third cell type Ill (alveolar brush cell) with cytokerat in 18 abundantly expressed but organized in an unusual intracellular ( ''globular'') structure. The latter cell type failed to bind the type II specific Maclura pomifera lectin, and contained no surfactant prote ins. Bronchial epithelial cells exhibited a more or less uniform stain ing pattern for cytokeratins 8, 18 and 19 and focally for cytokeratins 4 and 7.