Stimulation of Haemopoietic Colony Formation by Antilymphocyte Serum

Stimulation of endogenous and exogenous colony formation by antilymphocyte serum has been observed. The effect of ALS on endocolonization is associated with promotion of CFU recirculation. ALS‐induced stimulation of exocolonization was observed only with adult bone marrow cells of normal mice. ALS caused no effect on colony formation induced by embryonic liver cells or rapidly proliferating haemopoietic cells of early radiation chimeras. ALS did not cause an increase either in the content of CFU in the spleen or in their proliferating fraction. It is assumed that the ALS effect is exerted on the microenvironment and not directly on the CFU, as the result of which short‐range regulation of haemopoietic stem cell changes.