Contact Inhibition, Macromolecular Synthesis, and Polyribosomes in Cultured Human Diploid Fibroblasts.

The contact inhibition of locomotion in human cells has been described by Abercrombie.' When normal diploid fibroblasts growing on a glass surface come into contact, an adhesion forms and cell movement in that direction stops. As the resulting "monolayer" of diploid cells becomes confluent, their growth rate also decreases markedly.1' 2 In consequence, an upper limit is set for the population density of a given diploid cell culture which is not determined by properties of the medium. Human cell lines in which contact inhibition of growth is not operative (in general, heteroploid cells) form multilayered sheets in stationary culture, and attain population densities up to ten times those of human diploid cells. The present communication describes some of the molecular events associated with the decreasing growth rate of cultured human diploid cells as they become confluent. The possible causal role of cellular contact is also considered.