The enamel organ in the zone of transition between enamel secretion and maturation of 2-3-month-old kittens was examined by means of conventional electron microscopy. We subdivided the transition zone into the early and late transition regions. The ameloblasts in the early transition region were 30-45 μm in height and appeared as protein synthesizing cells with a well-developed rER-Golgi apparatus system and many secretion granules. They also contained various lysosomes such as dense bodies, multivesicular bodies, autophagosomes, and cytosomes containing granular materials. The distal cytoplasm of cell body was characterized by the presence of coated pits and vesicles and many secretion granules. Each ameloblast was connected firmly with adjacent ones by proximal and distal junctional complexes consisting of tight and gap junctions and desmosomes. These ameloblasts in the early transition region seemed to be still engaged in the rodless enamel formation. Moving towards the maturation zone, in the late transition region, shortening of ameloblasts became prominent and oval nuclei moved slightly towards the central part of cell bodies. Though the interameloblast spaces became wider than in the early transition region, the ameloblasts in the late transition region were still connected to each other by two sets of junctional complexes at the proximal and distal ends. In the supranuclear cytoplasm, the ameloblasts presented more pronounced vacuolar structures, some of which appeared to fuse to secretion granules and autophagosomes. The Golgi apparatus seemed to decrease its activity to produce secretion granules. The cytosomes containing cytoplasmic organelles were seldom observed in these transition ameloblasts. Throughout the zone of transition, the outer layer of enamel organ consisted of typical papillary layer cells having numerous mitochondria and long microvilli. From these results, we suggest a classification of the zone of transition between enamel secretion and maturation in the kitten enamel organ : the early transition region, the region of rodless enamel secretion; and the late transition region, the region of cell reorganization and termination of enamel matrix secretion.
It is supposed that cell-mediated immune response is an important factor in the pathogenesis of lichen planus (LP), and Langerhans cell (LC) is regarded to play a key role in initiating immune response. In this study, oral LP and leukoplakia were studied by the immunoperoxidase method using anti-S100 protein and monoclonal antibodies to estimate LC and T cell subsets. The number of LCs was found to be more numerous in LP compared with leukoplakia. In LP, OKT11 and OKT4 positive cells were predominant in subepithelial infiltrate, and fewer cells were stained with OKT8 monoclonal antibody. These results suggest an intimate relationship between LC and OKT4 positive cells in the pathogenesis of LP.