Thymic hormones and syngeneic T-lymphocytes are not required for leukopoiesis in an in vivo culture system for mouse bone marrow cells.

In order to explore the regulatory influence of thymic hormones and T cells on leukopoiesis , bone marrow cells from normal and athymic nude mice were cultured in peritoneal diffusion chambers (DC) that were implanted intraperitoneally into either normal or nude mice. T-cell-deficient nu/nu-C3H marrow cells formed slightly above normal numbers and nu/nu-BALB/c formed slightly below normal numbers of progenitor cells for granulocytes and/or macrophages in four-day DC cultures. Seven-day leukopoiesis in DC, as estimated by 3H-thymidine incorporation and differential cell counts, was not detectably affected by T-cell absence from nu/nu-BALB/c marrow. Leukopoiesis , including formation of progenitor cells, was not significantly different in normal and T-cell-deficient DC hosts. Normal thymocytes added to the T-cell-deficient bone marrow inocula decreased the generation of progenitor cells. These results indicate that (a) expansion of a proliferating granulocyte-macrophage progenitor cell population takes place in in vivo DC cultures without the presence of thymic hormones and T-lymphocytes, and that (b) T-lymphocytes may either stimulate or inhibit progenitor cell growth, and the balance between stimulation and inhibition apparently varies between mouse strains.