Interleukin 3 (IL-3) activity was demonstrated when inguinal lymph node cells obtained from Bacillus Calmette-Guérin-sensitized mice (BCG-ILNC) were stimulated in vitro with SSM, an
immunomodulator extracted from Mycobacterium tuberculosis. The
IL-3 activity was first detected on Day 1 in culture fluids of BCG-ILNC stimulated with SSM, reached a peak on Day 3, and then gradually decreased. The activity was completely neutralized by treatment with anti-murine
IL-3 monoclonal antibody (mAb). When BCG-ILNC were treated with anti-Thy 1.2 or anti-Lyt 1.2 mAb followed by
complement,
IL-3 was not produced in the culture fluids. However,
IL-3 in the culture fluids was detected when BCG-ILNC were treated with anti-Lyt 2.2 mAb, anti-asialo-GM1, or anti-mouse
immunoglobulin antiserum followed by
complement. These results suggested that Lyt 1+ T-cells appeared to be required for the production of
IL-3 from BCG-ILNC stimulated with SSM. In addition, low but significant
IL-3 activity was also observed in sera of mice treated with SSM. However, serum
IL-3 activity was not detected in mice treated with both SSM and Thy 1.2 or Lyt 1.2 mAb, whereas the activity was induced by SSM in mice treated with anti-Lyt 2.2 mAb or anti-asialo-GM1 antiserum. On the other hand, the in vivo growth of IMC
tumors inoculated in BALB/c x DBA/2 F1 mice was significantly decreased by
intralesional injection of culture fluids containing
IL-3, as well as by SSM itself. This antitumor activity of the culture fluids was not altered when it was treated with mAbs for
interleukin 1,
interleukin 2, or anti-mouse
gamma-interferon antiserum. The antitumor activity of the fluid was only eliminated when it was treated with anti-mouse
IL-3 mAb. Since nonspecific resistance to
tumors in mice stimulated with SSM appears to require Lyt 1+ T-cells, these results suggest that, in part, nonspecific resistance to
tumors of mice stimulated with SSM may be developed through
IL-3, which was produced by Lyt 1+ T-cells after SSM stimulation.