The mechanisms of action of anti‐tumour polysaccharides. I. The effects of antilymphocyte serum on the anti‐tumour activity of lentinan

Mechanisms of the regression of transplantated tumours in mice caused by lentinan, an anti‐tumour polysaccharide, were examined. 1) Lentinan showed a marked anti‐tumour effect when the animal was pretreated, starting 12 days before tumour inoculation. 2) The anti‐tumour effect of lentinan was blocked by injection of anti‐lymphocyte serum from 24 h after tumour transplantation. Lymphoid cells attacked by this serum apparently play an important role in tumour regression induced by lentinan. 3) Considering the selective actions of anti‐lymphocyte serum as an immunosuppressor, one of the mechanisms responsible for the anti‐tumour effect of lentinan may be the stimulation of cell‐mediated responses. 4) Humoral antibodies against lentinan do not seem to participate in tumour regression.