The FRTL-5 thyroid cell strain as a model for studies on thyroid cell growth.

Thyroid cell proliferation has been studied using an in vitro system of rat thyroid follicular cell strain (FRTL-5). While growing in continuous culture, this strain is still differentiated and non-tumourigenic. Both advantages and limitations in the use of such system for studies of thyroid cell growth should be considered. Some obvious limitations should be considered, such as the species (rat) from which FRTL-5 cells were originated, their long-term growth outside the animals, the presence of a chronic TSH stimulation. On the other hand, several advantages as the growth in hormonally and chemically defined media, their dependence upon TSH in the medium, their genetic homogeneity and their widespread use in many laboratories render the FRTL-5 strain a useful experimental tool. Studies on cell proliferation and mechanism of action of hormones, growth factors and human autoimmune IgG have been and are being performed, with the assumption that FRTL-5 cells are the in vitro equivalent of thyroid follicular cells.