Probable mechanism of spleen colony formation suppression with rabbit antimouse brain antiserum

Syngeneic thymocytes are shown to restore the capacity of bone marrow treated with rabbit antimouse brain (RAMB) serum to form the spleen colonies. The same effect may be exerted by the V fraction of thymosin or endotoxin, but not by allogeneic thymocytes. It is assumed that RAMB serum acts not on the stem cells but rather on another cell population (accessory cells?) contributing to the differentiation.