Characterization of NK cells and extrathymic T cells generated in the liver of irradiated mice with a liver shield

We previously reported that c-kit(+) stem cells which give rise to extrathy mic T cells are present in the liver of adult mice. Further characterizatio n of extrathymic T cells in the liver of adult mice is conducted here. When mice with a liver shield were lethally (9.5 Gy) irradiated, all mice survi ved. All tested organs showed a distribution pattern of hepatic lymphocytes on day 7. The distribution pattern in the liver was characterized by an ab undance of NK (CD3(-) IL-2R beta(+)) and extrathymic T cells (CD3(int) IL-2 R beta(+)) before and after irradiation. To determine their function, post- irradiation allogeneic bone marrow transplantation (BMT) was performed in m ice with or without a liver shield. Allogeneic BM cells were rejected in mi ce with a liver shield and specific activation of CD8(+) CD3(int) IL-2R bet a(+) cells was induced. At that time, potent cytotoxicity of liver mononucl ear cells (MNC) against allogeneic thymocytes was induced. Both NK1.1(+) an d NK1.1(-) subsets of CD3(int) cells expanded in these mice. An ipl vivo el imination experiment of the subsets indicated that the NK1.1(+) subset of C D3(int) cells (i.e. NK T cells) was much more associated with the rejection of allogeneic BM cells. However, even after the elimination of NK T cells, allogeneic BM cells were rejected. In this case, granulocytes expanded in parallel with NK1.1(-) subsets. Granulocytes may also be associated with th e rejection of allogeneic BM cells. These results suggest that the liver is an important haematopoietic organ even in adult life.