title: Radiation abrogation of myelopoietic inhibitors found in thymus-conditioned medium.
abstract: We have previously reported conditioned medium from cultures of murine 'nonlymphoid' adherent thymus cells to be a source of myelopoietic inhibitor substance(s). The inhibitor has a molecular weight of less than 1000 daltons. It is dialyzable. and its effects are reversible with washing, but it is not significantly cytotoxic. The inhibitor(s) abrogate both the 10-day granulocyte-macrophage colony-forming cell (GM-CFC) and the 25-day monocyte-macrophage colony-forming cell (M-CFC). Morphologically, cultures appear to be lymphocyte-free after 10-12 days, and consist primarily (80%) of nonspecific esterase positive cells and epitheloid appearing (20%), nonspecific esterase negative cells. Radiation of thymic cultures at 12 days reduces levels of inhibitor(s) found in the medium. Inhibitor levels from pooled samples collected over 4 days demonstrate reductions of 10% at 100 rads 15% at 200 rads, 25% at 300 rads, and 85% at 400 rads. The steepest area of radiation reduction occurs between 300 and 400 rads, with the interpolated 50% radiation reduction level at 342 rads. Analysis of once-harvested radiated culture supernates showed no significant inhibitors present when medium was examined 5-10 days postradiation.
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D003114:Colony-Forming Units Assay; D006098:Granulocytes / Q000166:cytology; D006410:Hematopoiesis / Q000528:radiation effects*; D008222:Lymphokines / Q000378:metabolism / Q000528:radiation effects*; D008264:Macrophages / Q000166:cytology; D051379:Mice; D009000:Monocytes / Q000166:cytology; D013950:Thymus Gland / Q000378:metabolism / Q000528:radiation effects*
chemical_list: D008222:Lymphokines; C022173:stem cell inhibitory factor