Migration and maturation of Langerhans cells in squamous metaplasia of the rat trachea induced by vitamin A deficiency

The migration and maturation of Langerhans cells (LCs) in rat tracheal squamous metaplasia due to vitamin A deficiency were investigated immunohisto-chemically and electron microscopically. In the early stage of metaplasia, i.e. basal cell hyperplasia, no LCs with Birbeck granules (BGs) could be found, but there were desmosome-free cells which had the morphological charcteristics of immature LCs. They were clearly different from inflammatory cells such as macrophages and lymphocytes, and were, therefore, considered to be precursors of LCs. In the stage of stratification, small numbers of Ia-and protein kinase C type II (PKCII)-positive cells were recognized. Ultrastructually they were immature LCs with ovoid nuclei, many free ribosomes and few dendrites. The cytoplasm was dark and a few BGs and atypical granules (AGs) could be seen in the Golgi area. In the early stage of cornification, LCs with partially intended nuclei, prominent nucleoli and well-developed Golgi complexes were found. There were many BGs and AGs and structures transitional between them in the Golgi areas. In epithelium showing mature squamous metaplasia, many Ia-and PKCII-positive dendritic cells could be seen. Most of these were typical mature LCs with lobulated nuclei, clear cytoplasm and prominent dendritic processes. The number of BGs and AGs was fewer than in the LCs found in the early stage of cornification, and these granules were distributed throughout the cytoplasm. In the final stage, where the basal cells had differentiated into a flatter epithelium, few LCs could be seen. These findings suggest that the precursors of LCs without BGs migrate into metaplastic squamous epithelium and mature into LCs forming BGs after exposure to the microenvironment of the squamous epithelium.