One of the first steps in an In-Cell Western Assay experiment is to seed cells into the wells of a tissue culture microplate. Cell density is more important for some cell lines than others. In particular, cells that depend more on extracellular activity for proliferation (such as epithelial cells) are affected to a greater extent by initial growth conditions. There are three factors to consider when seeding cells:
- Plates: For most adherent cells that stick to wells tightly (e.g. A431, HeLa, HEK293, CHO), we recommend regular tissue culture microplates with low auto-fluorescence, such as Nunc P/N 167008. For adherent cells that could detach from wells during In-Cell Western assay wash steps (e.g. NIH3T3), we recommend Poly-D-lysine coated 96-well microplates.
- Cell seeding density: Typically, 15,000 to 40,000 cells are seeded per well. Two to three days are usually required for cells to reach the appropriate confluency, depending on growth rate. Seeding with low cell numbers is recommended if you plan to culture for several days before use. Plates seeded with higher cell numbers will be ready to use earlier.
- Confluence: To obtain maximal fluorescent signals, complete or near complete confluency is recommended for cells that stick to wells tightly. For cells that adhere loosely to wells, such as NIH3T3, 70% confluency should be used. Please note that cell type and experimental conditions may affect the acceptable level of growth confluency.
The example below illustrates the importance of cell seeding density for A431 cells. As shown in the corresponding graph, cell growth is greatly inhibited when there are too few neighboring cells.