The Influence of Thymus Cells in Hemopoiesis: Stimulation of Hemopoietic Stem Cells in a Syngeneic, In Vivo, Situation

Using the spleen colony-forming techniqueto assay hemopoietic stem cells, (CFUs)experiments have been carried out to investigate the role of thymus cells in hemopoiesis. The experiments were carried outby injecting live or killed thymus cells intolethally-irradiated mice together withhemopoietic tissue containing CFUs. Theeffect of thymus cells on endogenouscolony formation in sublethally-irradiatedmice was also investigated. Colony formation by normal bone marrow or spleen isunaffected by the addition of thymus cells,but cell populations damaged by radiationall demonstrate increased colony numberswhen live thymus cells are injected within48 hr of initiating colony formation. Endogenous colony formation resulting from anx-ray dose of 475 red is increased 2.9times: exogenous colony formation frombone marrow or spleen populations whoseCFUs content has been reduced to approximately 20% of normal with 180-rad-rays is increased 2.1 times. Studiesinvestigating this enhancement demonstrate that at least some of the colonyforming cells require the cooperation oflive thymus cells. Under the conditions ofthese experiments, at least 10⁶ thymuscells must be injected to produce maximum enhancement.

Submitted on November 27, 1972 Revised on January 29, 1973 Accepted on February 16, 1973