Bone marrow contains pluripotent stem cells which give rise to colonies when injected into irradiated syngenic hosts as well as more differentiated progenitor cells of the myeloid cell which are able to form colonies in vitro. Antisera against brain is known to contain antistem cell antibody. The present experiments were designed to determine if the myeloid progenitor cell still expresses the stem cell antigen.

Bone marrow cells were treated with antibrain antiserum plus complement and then survival of stem cells was determined by injection into irradiated hosts. Survival of myeloid progenitor cells was determined by culturing the cells in vitro. It was found that stem cells were eliminated by the antiserum but that myeloid progenitors were not. Inefficient in vitro lysis was ruled out as the reason for this difference since in vitro colonies were not reduced when the cells were treated with anti-immunoglobulin or after passage through an irradiated host. In the differentiation from stem cell to myeloid progenitor there is an associated surface antigen change.

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