Toxicity studies with cellular models of differentiation.

Recently a variety of models have been developed in several laboratories to allow the study of various types of tissue differentiation processes from species ranging from lower animals to mammals. If the use of in vitro systems is intended to reveal toxic effects, two main lines of application may be envisaged (a) toxic effects, for which some indication already exists, can be further characterized and the mode of their toxic action clarified ('secondary testing'), and (b) toxic effects, previously unknown, can be detected ('primary testing'). Primary testing is difficult, regarding not only the strategy to be used and the validation of the system, but also the extrapolation of data to the situation which possibly exists in man. Due to these reasons, this approach has so far not been successfully applied with any group of chemicals.