The paradoxical effects of thioglycollate-induced macrophages on the growth of B16 melanoma cells in vivo and in vitro.

The effect of thioglycollate-induced macrophages on the growth of syngeneic B16 melanoma cells was studied. Thioglycollate-induced macrophages showed strong cytostasis and cytotoxicity towards B16 tumor cells in vitro. However, these effects were not demonstrable in an in vivo assay which involved local transfer and experimental metastasis. In contrast to the in vitro results, mice injected iv with both B16 tumor cells alone. Possible reasons for the failure of thioglycollate-induced macrophages to exhibit cytostatic and cytotoxic activity in vivo are discussed.