Abstract. Mouse interferon preparations inhibited the multiplication of mouse leukemia L 1210 cells in stationary suspension cultures. The degree of inhibition was found to correlate with the antiviral titer of the interferon preparations. The factor(s) responsible for inhibition of L 1210 cell multiplication could not be dissociated from interferon by standard physicochemical means.
Abstract. Previously published studies concerning the proliferative changes, during ageing in vitro, of human embryonic fibroblasts, have been reappraised. The data suggest that the changes occur through shifts in a whole spectrum of cells between two extremes: complete inhibition and a normal division cycle. Reversion from the non‐dividing to the dividing state becomes increasingly difficult and random. Ageing is the result of a long chain of events that hinder the transit of cells through the division cycle, mainly through interference with the G1 but also with the G2 period. Some metabolic events at the very end of the lifespan could support the terminal differentiation hypothesis.
The growth properties of fibroblasts from the thoracic skin of patients with mammary cancers were compared to those of fibroblastic cultures from patients with benign lesions or having undergone surgery for non-neoplastic diseases. As expected, an inverse correlation was found between the doubling potential of fibroblasts in vitro and the donor's age for cells from patients with benign lesions; however no correlation, was found with cultures from cancer patients. Moreover, the latter group responded in an abnormal way to three biological parameters: anchorage dependence, colony formation on monolayers of normal human epithelial cells and saturation densities in overcrowded culture conditions. Skin fibroblasts from one patient with a benign lesion, whose mother had developed a breast cancer, displayed all the abnormal growth properties. Periodic controls of this patient resulted in the early detection of a carcinoma 3 years after the first operation for a benign microcystic lesion. Finally, we found that multiple subcultivations in overcrowded culture conditions cause the selection of a fibroblastic cell subset with greater growth potential which, in the cell strain tested, could invade foreign tissue in vitro.
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