BRONCHIAL EPITHELIUM ASSOCIATED TO LYMPHOID-TISSUE DOES NOT SELECTIVELY EXPRESS VIMENTIN

The existence of a lymphoepithelium containing M cells in the bronchus -associated lymphoid tissue (BALT) of several species has repeatedly b een questioned. In previous electron microscopical studies we failed t o ultrastructurally identify these cells in the epithelium covering br onchial lymphoid tissue of adult rats. In the present study, we analyz e immunohistochemically the expression of vimentin, an intermediate fi lament, reported to be a sensitive marker for rabbit M cells, in both BALT and Peyer's patches. Our results demonstrate, however, the absenc e of vimentin expression in the epithelium covering the bronchial lymp hoid aggregates as well as in the lymphoepithelium of the Peyer's patc hes. On the contrary, both epithelia are strongly cytokeratin positive . Furthermore, numerous vimentin-positive lymphocytes appear in both l ymphoid organs. Results are discussed from a view of the possible rela tionship between BALT and the so-called mucosae-associated lymphoid ti ssue (MALT).