Interrelationships of myeloid and lymphoid cells: studies with chromosome-marked cells transfused into lethally irradiated mice

Abstract

Lethally irradiated CBA mice were injected with a mixture of two cell suspensions, syngeneic with each other and with the host, but distinguished by the presence of either one or two T6 marker chromosomes. One of the cell suspensions was derived from adult bone marrow (10 5 cells), the other from adult thymus or pooled lymph nodes or thoracic duct lymph (10 7 cells). The recipients were killed between one day and one year after irradiation, having been injected 1 ½ h previously with Colcemid. Their bone marrow, spleen, thymus and lymph nodes were studied cytologically, and counts were made of the numbers of mitotic cells derived from the two donor cell suspensions and from the irradiated host. Bone marrow, spleen and thymus were all recolonized predominantly or exclusively by descendants of injected bone marrow cells. Descendants of injected lymphoid cells were seen in substantial numbers only in the lymph nodes, where they formed the majority of the total dividing cells between 1 and 3 weeks after irradiation. After that the proportion of such cells in the lymph nodes decreased gradually, in favour of bone marrow-derived cells, but they did not disappear completely. Lymphoid cells were equally unsuccessful at recolonizing the myeloid and thymic tissues of mice given a high sublethal dose of irradiation (800 rad) without bone marrow therapy. The normality of the repopulated lymph nodes and thymus was verified histologically and by two functional tests involving the capacity of cells rapidly to recolonize the lymph nodes or form macroscopic haematopoietic nodules in the spleen of further lethally irradiated mice. A small and decreasing amount of haematopoiesis was found in the lymph nodes during the first 2 months after irradiation, but not in the thymus.