[Differentiation and a change in the sensitivity to antibrain serum of circulating colony-forming units under the action of thymic factors].

The rabbit anti-mouse brain serum (RAMBS) that interacts with SC-1 marked cells, rather than with thymocytes and bone marrow cells, inhibits most of the blood and bone marrow colony-forming unit (CFU) population. A commercial thymus preparation thymalin increases the granulocytopoietic activity of the circulating CFU and decreases their sensitivity to RAMBS in thymectomized and normal animals. Differentiation of circulating CFU remains unchanged in thymalin-treated mice after RAMBS administration, while CFU erythroid activity of nontreated animals is lowered. The revealed changes in the CFU differentiation and sensitivity to RAMBS confirm the assumption that SC-1 antigen may mark Thy-1 lymphocytes of their microenvironment, rather than CFU.