Differential Effects of IL-2 and IL-6 on the Development of Three Distinct Precursor T-Cell Populations in the Thymus

Three distinct T-cell precursors: bone marrow cells that express low levels of the Thy-1 antigen but no lineage markers (Thy-1-lo/BM); CD4(-), CD8(-), and CD3(-) thymocytes that express low levels of the Thy-1 antigen (Thy-1-lo/Thym); and CD4(-), CD8(-), and CD3(-) thymocytes that express high levels of the Thy-1 antigen and the IL-2 R α chain (Thy-1(+)/ IL2R(+)) were isolated by fluorescence-activated cell sorter (FACS). These three populations expanded with different kinetics in the thymus of irradiated recipient mice after intrathymic transfer. When a high dose of human recombinant IL-2 (r-IL-2) or human recombinant IL-6 (r-IL-6) was administered, r-IL-6 accelerated donor Thy-1(+)/IL2R(+) to differentiate, whereas r-IL-2 blocked normal differentiation and expansion of donor Thy-1-lo/Thym, but did not show any significant effect on donor Thy-1(+)/IL2R(+). Neither r-IL-2 nor r-IL-6 worked directly on donor Thy-1-lo/BM in this transfer system.