A VARIANT EPITHELIAL SUBPOPULATION IN NORMAL THYROID WITH HIGH PROLIFERATIVE CAPACITY INVITRO

We describe the existence in normal human primary thyroid cultures of a hitherto unrecognised sub-population of epithelial cells. This varia nt phenotype is characterised by squamoid morphology, absence of thyro globulin, and an altered profile of intermediate filament expression. We suggest that these cells are derived from scattered foci of squamou s metaplasia present in the normal gland. Although they are initially present at a frequency of less than 10(-4), their very high proliferat ive capacity enables them to outgrow the 'classical' follicular cells and confers a much increased capacity for gene transduction. Recogniti on of these cells is therefore crucial in the interpretation of long-t erm thyroid culture experiments and those involving in vitro gene tran sfer.