Bone Marrow as the Major Source of Potential Immunologically Competent Cells in the Adult Mouse

Abstract

PREVIOUS work from this laboratory^1–4 has suggested that immunologically competent cells are derived from foetal liver during embryonic life and that their ‘functional maturation’, or proliferation, or both, is dependent on the residence of these cells in thymic tissues. The source of these lymphoid precursor cells during adult life is not known. Using chromosomally marked cells, it has been shown, however, that when cell suspensions of various adult lymphoid tissues are injected into lethally irradiated mice only those cells derived from bone marrow are found in the thymus of the host in significant numbers; while the cells from other lymphoid tissues readily proliferate in the peripheral lymphoid tissues of the host, they are only rarely found in the thymus⁵. In experiments involving the restoration of immunological competence in lethally irradiated thymectomized adult mice, Miller et al.⁶ concluded that “marrow cell suspensions lack adequate numbers of immunologically competent cells but contain precursor cells” which mature under the influence of the thymus. Furthermore, Feldman and Globerson⁷ have reported work which suggests that the immunological reactivity manifested by thymectomized mice which have been lethally irradiated, but protected with bone marrow cells and restored to immunological competence with an allogeneic thymic graft, may be due to the donor marrow cells rather than to cells from the thymic graft. Taken together, these results suggest that bone marrow is the source of potential immunologically competent cells in the adult. It is the purpose of this communication to present data which suggest that bone marrow may be the major, or perhaps sole, source of lymphoid precursor cells in the adult mouse.