Suppression of antibody-sensitized tumor cells by macrophages: insufficient supply or activation of macrophages within large tumors.

Systemic administration of antibody against the C3H lymphosarcoma 6C3HED caused complete suppression of the growth of 10(5) tumor cells. When the size of the tumor inoculum was increased to 10(6) tumor cells, excess antibody was unable to cause complete suppression unless exogenous macrophages were added to the tumor inocula. The decreased effectiveness of antibody was shown to be caused by a local deficiency in the supply or activation of macrophages within the large tumor grafts and not by a systemic deficiency.