Immunoregulatory changes induced by total lymphoid irradiation (TLI). I. Appearance of a population of cells bearing the thymus leukemia (TL) surface antigen in the lymph nodes and spleen.

BALB/c mice were treated with total lymphoid irradiation (TLI; 3400 rads) or single-dose, whole-body irradiation (WBI; 550 rads), and the lymph nodes and spleen were assayed for the level of H-2, Ia, Thy-1.2, Lyt-1.2, Lyt-2.2,3.2, and TL-bearing cells by an in vitro cytotoxicity assay. The level of cells bearing all these markers, except for TL, was similar to that observed in normal unirradiated mice. The level of TL+ cells was increased 10- to 20-fold in the TLI-treated mice as compared to WBI-treated mice or normals. The increased number of TL+ cells persisted for at lest 200 days after radiotherapy, and was not dependent upon irradiation of the thymus. However, thymectomy before TLI prevented the subsequent development of peripheral TL+ cells. The findings suggest that this abnormal subpopulation of T cells develops as a result of changes in the peripheral lymphoid tissue microenvironment induced by TLI.