Clonal interactions in fibroblast proliferation: recognition of self vs. non-self.

The proliferation and aging of fibroblast populations has been postulated to include a process of clonal selection. Using carbocyanine dyes to label clonal fibroblast populations, we were able to follow their growth in mixed cultures. Individual fibroblast clones seeded as the minority population (20%) with either another clone or the parent line (differentially labeled) always demonstrated increase relative growth so that, by the end of 4 weeks, approximately equal numbers of both populations were present. Labeled cells of the same clone mixed as the minority population with differentially labeled cells of the same clone maintained their minority status. The results indicate that clonal populations of fibroblasts are able to recognize "self" as different from "non-self" and that this recognition leads to alterations in cellular proliferation.