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 inter esting dynamic expression during tooth development. It is first expressed i n the reduced enamel epithelium, its expression then increases in the orall y faced reduced epithelium and the overlying oral epithelium that then fuse to give rise to the junctional epithelium. The expression of CEACAM1 remai ns at high levels in the junctional epithelium, in contrast to the surround ing oral sulcular epithelium which shows much lower expression levels. We i nvestigated if the high expression levels of CEACAM1 and the loosely organi zed cells characteristic of the junctional epithelium are genetically progr ammed or result from bacterial infiltration. Methods: Oral tissues from germ-free rats and mice and animals with convent ional bacterial flora were analyzed by transmission electron microscopy and immunohistochemical staining for CEACAM1. Results: The junctional epithelium of both germ-free and conventional anima ls was identical with respect to both CEACAM1 expression and morphology. Al so the presence of leukocytes was the same in both types of animals. Conclusions: The results indicate that the characteristic morphology and th e high expression levels of CEACAM1 in the junctional epithelium are geneti cally programmed and not a result of bacterial infiltration. This suggests that CEACAM1 has an important role for the structural integrity of the junc tional epithelium. This conclusion was supported by the observation that th e junctional epithelium does not express any E-cadherin, which is another a bundant epithelial cell adhesion molecule.