Effects of thymocytes on marrow cells from normal and busulfan-treated mice

To study the effects of thymocytes on hemopoiesis, we 1) cocultured marrow cells with and without thymocytes in an erythroid burst (BFU-E) culture system, 2) injected marrow cells with and without thymocytes into supralethally irradiated mice to assay CFU-S, and 3) assessed the survival of supralethally irradiated mice transplanted with marrow cells with or without thymocytes. The marrow cells used were either from mice given six injections of busulfan and then permitted to rest for 2, 5, or 10 weeks or from mice treated similarly with the busulfan vehicle alone. Thymocytes did not alter spleen surface colony counts or survivorship in any of the test groups. Thymocytes did effect an increase in BFU-E cultured from marrow obtained from the vehicle-treated mice but not from marrow of busulfan-treated mice. Thus, in addition to decreasing the population of hemopoietic precursors in the marrow, busulfan alters the nature of the remaining early erythroid precursor cell population rendering it unresponsive to thymocytes in vitro.