[Growth stimulation in a Ewing sarcoma after "macrophage blockade" in athymic (nude) mice]

Inoculation of cell suspensions of a Ewing sarcoma (1.5 to 2.0 x 10(8) viable cells/mouse) into thymus less nude mice bred under conventional conditions gave a 90% take rate after subcutaneous injection and 35% after intraperitoneal. Intraperitoneal take rate is raised to 90% by intraperitoneal pretreatment with India ink. The same pretreatment shortens the tumor doubling time after subcutaneous inoculation. Both events are probably caused by inhibition of macrophages and/or natural killer cells.