Bronchial epithelium associated to lymphoid tissue does not selectively express vimentin

Abstract

The existence of a lymphoepithelium containing M cells in the bronchus-assmiated lymphoid tissue (BALT) of severa1 species has repeatedly been questioned. In previous electron microscopical studies we failed to ultrastmcturally identify these cells in the epithelium covering bronchial lymphoid tissue of adult rats. In the present study, we analyze immunohistochemically the expression of vimentin, an intermediate filament, reported to be a sensitive marker for rabbit M cells, in both BALT and Peyer's patches. Our results demonstrate, however, the absence of vimentin expression in the epithelium covering the bronchial lymphoid aggregates as well as in the lymphoepithelium of the Peyer's patches. On the contrary, both epithelia are strongly cytokeratin positive. Furthermore, numerous vimentin-positive lymphocytes appear in both lymphoid organs. Results are discussed from a view of the possible relationship between BALT and the so-called mucosaeassociated lymphoid tissue (MALT).