In Vivo Generation of Mouse Natural Killer Cells: Role of the Spleen and Thymus

The role of the spleen and thymus was investigated in the natural killer (NK) cell system. These NK cells have the ability to kill a variety of tumour cells as demonstrated in vitro in short-term ⁵¹Cr release assays. The work presented deals with three observations: (1) the effect of splenectomy on the levels of NK activity in the blood and lymph nodes. (2) the effect of splenectomy on the reconstitution of irradiated animals with bone marrow cells, and (3) the level of NK activity in adult thymectomized, irradiated animals which were reconstituted with bone marrow or thymus cells from either high or low NK activity animals. Thus, for the third point, chimaeras were established between histocompatible strains of mice A. BY (a low NK strain), and C57B1/6 (a high NK strain). The ability of T cells from one strain could then be observed to either help or suppress the NK activity of the bone-marrow-derived cells. The data presented show that the absence of a spleen does not affect MK activity or reconstitution of NK cells in irradiated animals. Further, T cells from one strain do not affect NK activity of animals reconstituted with bone marrow cells from a histocompatible strain. Thus T cells from a low NK stain (A. BY) did not suppress the high activity of C57B1/6 cells, and, conversely, the C57B1/6 T cells did not compensate for the low NK activity of A. BY cells.