RESUMO
Foetal bovine serum (FBS) and the preparation Ultraser (LKB, Sweden) contain more growth factors (GF) necessary to promote proliferation of cells in soft agar than the sera from newborn and adult animals. It was found that non-dialysable GFs are produced during growth of cells in semisolid medium. The dependence of colony-forming efficiency (CFE) on plating cell dose (PCD) was studied in 11 cell lines at varying concentrations of FBS. Cell proliferation depended on both serum and cell GFs. The minimum serum concentration at which CFA is not dependent on PCD can be selected for each cell line and, therefore, serum GFs completely compensate for the lack of cell GFs. Serum GFs within a certain range are, conversely, complemented by cell GFs: the minimum plating cell dose capable of compensating for the lack of serum GFs can be determined for each cell line.