Macrophage Dependent Protection of Tumour Cells.

Rat lymphoma cells sensitized with antibody and incubated with normal macrophages were shown to become resistant to damage from cytotoxic antibody and complement or cytotoxic lymphocytes. Both lymphoma specific antibody and normal macrophages were required to produce protection. The cytotoxic effect of lymphocytes or antibody with complement and the protective effect of antibody with macrophages was assessed by 51Cr release and by loss of capacity of iymphoma cells to transfer the disease to syngeneic rats. No cytotoxic effect could be attributed to macrophages from sensitized allogeneic rats. Inhibition of phagocytosis by Cytochalasin B did not destroy the capacity of macrophages to protect lymphoma cells. Sodium fluoride, however, did block the protective effect. It is envisaged that this protective phenomenon may be of importance in understanding some aspects of growth of tumours in vivo despite the presence of immune cytotoxic mechanisms. [ABSTRACT FROM AUTHOR]