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Interactions between epithelial and fibroblast-like cells in cultures derived from monkey periodontal ligament.

Explants of adult monkey periodontal ligament produced outgrowths containing both fibroblast-like (F) and epithelial-like (E) cells. A number of multilayers of either E or F cells, or both E and F cells were seen. Electron-microscopic examination of mixed multilayers showed that E cells could form, either the superficial or deep sheet of cells. Attachments by means of desmosomes between dorsal and ventral surfaces of multilayered E cells were demonstrated. Although the membranes of E and F cells were sometimes closely apposed, no special junctional structures could be detected between them. The E cell and F cell layers were also observed in a relationship, unusual for cell culture, in which the E cell layer was sandwiched between two F cell layers. This unusual relationship may be the result of cells mimicking in vitro their relationship in vivo, since the E cells are derived from the epithelial rests of Malassez which, in vivo, are surrounded by periodontal ligament F cells. When F cells were seeded on to the surface of E cells a significant fraction of them were found to attach, but the spreading of F cells on E cells was a rare event. These observations could be interpreted as being the result of heterogeneity in the F cell populations. A further indication of the heterogeneity of F cell populations was provided by time-lapse studies of colonies of F cells obtained by culturing cell suspensions of porcine periodontal ligament. In this system, it was found that statistically significant differences existed between the different F colonies with respect to their average cellular mobility. These findings suggest that light-microscopical morphological criteria do not adequately define cell types in terms of behavioural or functional characteristics.