Modulation of B and T cell subsets in mice treated with fractionated total lymphoid irradiation (TLI). IV. Expression of TL4-bearing cells in spleen and bone marrow of TLI-treated mice.

The pre-thymic cell phenotypes arising in spleen and bone marrow (BM) of fractionated total lymphoid irradiation (TLI)-treated mice are characterized in this paper. Different strains of mice received 200 rad lymphoid irradiation daily for 8 to 10 days. At different time intervals after treatment, BM or spleen cells of treated mice were stained with a battery of antisera directed specifically to TL and Thy-1 antigens. Analysis of the stained cells on a fluorescence-activated cell sorter (FACS) apparatus revealed that 10 to 30% of spleen or BM cells of TLI-treated mice were TL+ cells whereas no TL+ cells could be found in the same organs in the normal untreated mice. The appearance of TL+ cells in the spleen and BM of TLI-treated mice was found to be thymic independent, as thymectomy of mice neither prevented nor altered the kinetics of TL+ cell appearance. The sequence of antigenic marker appearance reveals that TL markers precede Thy-1 markers and that TLaa markers precede TL4 antigen. The relevance of the TL4+ cells to the development of leukemias is discussed.