Development of three Thy 1 + cell populations induced by distinct thymic stromal elements.

Thymectomized, X-irradiated mice, reconstituted with T cell-deprived bone marrow, were treated for 10 weeks with various thymic stromal fractions. Their splenocytes were then assayed for Thy 1 antigen. Three Thy 1 + populations were identified: cells of population 1 were found in mice treated with a membrane extract of thymic stroma. They had a high Thy 1 concentration which could be reduced (Population 2) after incubation with a thymic hormone preparation (STF). Population 3 was also composed of high Thy 1 cells but these were induced by STF treatment in vivo and could not be further differentiated into low Thy 1 cells.