Importance of lyt 1⁺ t-cells in the antitumor activity of an immunomodulator, ssm,¹ extracted from human-type tubercle bacilli²

An arabinomannan lipid extracted from Mycobacterium tuberculosis strain Aoyama B (SSM) is an immunopotentiating agent with interferon-inducing and antitumor activities. In the present study, the possible role(s) of various immunocompetent cells on the antitumor effect of SSM was investigated in mice bearing syngeneic (RL♂1 leukemia) and allogeneic (Ehrlich carcinoma) ascites tumors. When Thy 1⁺ T-cells were depleted from tumorbearing mice by the administration of monoclonal anti-Thy 1.2 antibody, the protective effect of SSM was eliminated. However, when macrophage (Mφ) and natural killer (NK) cell activities were depleted by treatment with Mφ blockers (trypan blue and carrageenan) or a blocker for NK cells (anti-asialo GM1 antiserum), no alteration of the antitumor' activity of SSM was observed. Therefore, T-Iymphocytes, but not Mφ or NK cells, were required for the expression of the antitumor efficacy of SSM. The antitumor activity of SSM was also abrogated by Lyt 1⁺ T-cells being depleted by treatment with monoclonal anti-Lyt 1.2 antibody, whereas the administration of monoclonal anti-Lyt 2.2 antibody had no effect on the antitumor activity. Independent of Mφ, NK cells, or Lyt 2⁺ T-cells, Lyt 1⁺ T-lymphocytes appear to play an important role in the expression of the antitumor effects of SSM.