The cytotoxic effect of mouse macrophages stimulated in vitro by a beta-1,3-D-glucan from yeast cell walls.

Macrophages stimulated by an insoluble beta-1,3-D-glucan from yeast cell walls were able to destroy tumour cells as measured by the release of radioactive label from prelabelled 14C-thymidine cells. Target cells were B-16 melanoma, P-815 mastocytoma, and the L-929 cell line. A significant target cell killing by macrophages stimulated by glucan was observed after 72-96 h. The cytolysis of L-929 cells was investigated in some detail. No stable soluble cytolytic factor appeared to be released into the medium during the stimulation of macrophages by glucan, since cell-free spent medium had no cytotoxic effect on L-929 cells. The densities of the macrophage monolayers were critical for an effective target cell killing; dense cultures showed more cytotoxicity than less dense cultures. The kinetics of the development of macrophage-mediated cytotoxicity suggests a minimum stimulation period of 4 days for maximal cytolysis.