Relationship of Bacillus Calmette-Guérin-induced suppressor cells to hematopoietic precursor cells

Bacillus Calmette-Guérin (BCG) stimulated the proliferation of granulocyte-macrophage colony-forming cells (CFU) and activated suppressor cells that inhibit the immunization of T-lymphocytes in vitro. Increases in both CFU concentration and suppressor cell activity were moderate in the bone marrow and marked in the spleen of mice given BCG i.v. In the bone marrow, these increases were apparent 2 days after treatment with BCG, while in the spleen they did not occur until 7 days after BCG. A BCG strain that produced no increases in CFU concentration also produced no activation in suppressor cell activity. Fractionation of spleen cells through nylon wool and density gradients revealed that cell populations enriched in CFU were also enriched in suppressor cell activity. The paralelism in the response to CFU and suppressor cells to BCG indicates that there is a close relationship between these two cell populations.