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Abstract The development of colonies in nutrient agar in vitro from mouse hemopoietic cells, in the presence of a maximal dose of colony-stimulating activity (CSA), was greatly enhanced by the addition of washed red cells to the culture system. Human, sheep, guinea pig, rat, and mouse (syngeneic or allogeneic), but not rabbit, red cells exhibited enhancing ability, as did osmotically lysed erythrocyte preparations from rats. The use of red cells in the culture system, in addition to a maximum concentration of CSA, has resulted in revised estimates of the numbers of agar colony-forming units in hemopoietic tissues.
Bradley et al. (Wed,) studied this question.