The development of NK cell activity in thymectomized bone marrow chimaeras.

Most of the natural killer (NK) cells, recently derived from the bone marrow (14 days after injection of bone marrow cells into lethally irradiated mice), express the Thy-1 antigen; after some period of time (by day 28) a normal proportion (50%) of Thy-1+ NK cells is found. This study demonstrates that the shift of these Thy-1+ NK cells to Thy-1- NK cells is influenced by the thymus: NK cells developing in the total absence of the thymus--bone marrow (bm) cells from adult thymectomized (Tx) or nude (nu) mice injected into thymectomized recipients, (Tx) bm----(Tx) or nu bm----(Tx)--remain Thy-1+, while the presence of the thymus at some stage of the NK cell maturation--bone marrow cells injected into thymectomized recipients, bm----(Tx), or normal recipients reconstituted with bone marrow cells from thymectomized or nude mice, (Tx) bm----or nu bm----normal recipients--is sufficient for the development of normal ratio of Thy-1+ and Thy-1- NK cells.