Release of a mitogenic factor by splenic Lyt 1⁺ T-cells from mice treated with SSM, an immunomodulator extracted from human type tubercle bacilli

A production of the soluble factor activity in culture fluids of murine splenic mononuclear cells (SMNC) treated with SSM, an immunopotentiator extracted from Mycobacterium tuberculosis strain Aoyama B, was investigated. The soluble factor activity was determined as a mitogenic activity released from SMNC of mice previously treated with a 500 μg/kg dose of SSM (primed SMNC). The mitogenic activity was produced when primed SMNC were challenged in vitro with SSM at a concentration of 5 μg/ml. The activity was not produced in culture fluids of primed SMNC treated with anti-Thy 1.2 or anti-Lyt 1.2 monoclonal antibody plus complement followed by a challenge with SSM. However, the production of the activity was not affected by pretreatment of primed SMNC with anti-Lyt 2.2 monoclonal antibody plus complement. Since the non-specific resistance to tumors of mice stimulated with SSM was not demonstrated in mice depleted of Thy 1⁺ and Lyt 1⁺ T-cells, and Lyt 1⁺ T-cells from SSM-treated mice did not show any direct cytotoxic activities against tumor cells in vitro, the soluble factor released from Lyt 1⁺ T-cells by SSM stimulation may play an important role in developing the non-specific resistance of mice treated with SSM.