On the formation of orientated protrusions in confrontation cultures of human diploid and tumor cells.

Wi38 cells (diploid human embryonic lung fibroblasts) were cultivated for 24 h on cover slips, following which HeLa cells (a monolayer and a suspension subline) were seeded on top of the fibroblasts. Some tumor cells lay on the glass between fibroblasts and by some means induced the Wi38 cells to form protrusions orientated towards the tumor cells. By statistical methods it has been shown that the outgrowth of these protrusions is a non-random process that is not restricted to either normal or the tumor cells. This contact behavior can only be explained by the assumption of an exchange of signals and a chemotactic mechanism must be assumed.