Numerical evaluation of the invasion of closely related cell lines into collagen type I gels.

Cells were seeded on top of a reconstituted collagen gel layer, and their migration into the gel was evaluated as an assay for invasive behavior. The method was standardized by measuring the depth of migration of each cell in a defined volume of the gel. We developed a microscope stage, controlled by a computer program. This semiautomatic counting method allowed precise vertical localization of each cell in a collagen gel with an error of less than 0.1 micron. To test the discriminative power of the assay, we used cell lines which were known to be invasive or noninvasive in other assays. Closely related variants of 2 cell families were chosen: (1) one family derived from a mouse mammary gland (NMuMG), and (2) one derived from a mouse T cell lymphoma (BW5147). The assay could discriminate between invasive and noninvasive variants of related cell lines within the same family. The profile of the number of cells in each layer of the gel provided additional discrimination between the different cell lines. Furthermore, the assay allowed direct microscopic observation of cells migrating in the collagen gel. The present standardization makes the collagen assay suitable for semiautomatic testing of the invasive phenotypes in cell populations from the same as well as from different cell families.