Role of Thy-1 antigen in the in vitro differentiation of a rat mammary cell line.

A line of rat mammary cells, LA7, undergoes differentiation into domes or ridges or projections under partial medium control. Immunofluorescent studies show that at the time of dome formation the LA7 cultures express the Thy-1 antigen at the borders between cells. Exposure of the cultures to certain monoclonal anti-Thy-1.1 sera prevents formation of new domes and causes disappearance of preexisting ones; antisera to whole cells produce no visible effect. Cultures exposed to anti-Thy-1 sera at effective concentrations of antibody against domes show morphological changes and ridge formation. It seems that the specific interactions of these antisera with the Thy-1 antigen redirects the differentiation program of the cells.