The characteristic cellular organization and CEACAM1 expression in the junctional epithelium of rats and mice are genetically programmed and not influenced by the bacterial microflora

Background: The epithelial cell adhesion molecule CEACAM1 exhibits an interesting dynamic expression during tooth development. It is first expressed in the reduced enamel epithelium, its expression then increases in the orally faced reduced epithelium and the overlying oral epithelium that then fuse to give rise to the junctional epithelium. The expression of CEACAM1 remains at high levels in the junctional epithelium, in contrast to the surrounding oral sulcular epithelium which shows much lower expression levels. We investigated if the high expression levels of CEACAM1 and the loosely organized cells characteristic of the junctional epithelium are genetically programmed or result from bacterial infiltration. Methods: Oral tissues from germ-free rats and mice and animals with conventional bacterial flora were analyzed by transmission electron microscopy and immunohistochemical staining for CEACAM1. Results: The junctional epithelium of both germ-free and conventional animals was identical with respect to both CEACAM1 expression and morphology. Also the presence of leukocytes was the same in both types of animals. Conclusions: The results indicate that the characteristic morphology and the high expression levels of CEACAM1 in the junctional epithelium are genetically programmed and not a result of bacterial infiltration. This suggests that CEACAM1 has an important role for the structural integrity of the junctional epithelium. This conclusion was supported by the observation that the junctional epithelium does not express any E-cadherin, which is another abundant epithelial cell adhesion molecule.