Growth stimulation by direct cell-cell contact (contact stimulation) in normal human lung fibroblasts.

Clonal growth of the normal human lung fibroblasts, IMR-90, is stimulated efficiently by utilizing feeder fibroblasts. Under the sparse culture conditions, IMR-90 cells located close to the feeder cells formed colonies with a higher efficiency than those isolated from the feeders within the same dish. The IMR-90 cells in direct contact with the 3T3 cell feeders, as monitored by metabolic cooperation, showed a faster entrance into S phase than did the IMR-90 cells isolated from the feeders. The isolated cells, even when they remained closer to the feeder cells, entered S phase later than those of the IMR-90 cells making direct contact with the feeders with long pseudopods. Medium- and dish-surface-conditioning with the feeders resulted in marginal improvement of the clonal growth. These observations suggest that contact stimulation of growth occurs in sparse cultures of normal human lung fibroblasts.