ANTI-TUMOR CYTO-TOXIN FROM MACROPHAGES - NO CORRELATION BETWEEN CYTO-TOXIN ADSORPTION BY TUMOR-CELL LINES AND THEIR CYTO-TOXIN SUSCEPTIBILITY

Abstract

Mononuclear phagocytes can synthesize a cytotoxin, similar to that in tumor necrosis serum, which is cytotoxic to certain tumor cell lines in vitro. This study investigated whether susceptibility and resistance to the cytotoxin can be explained in terms of the amount of cytotoxin receptor expressed on the tumor cell surface. Binding of cytotoxin was quantitated by direct adsorption and competitve inhibition assays with cytoxin-resistant or -susceptible tumor lines and with sublines of susceptible lines selected for resistance to the cytotoxin. For both rabbit and human cytotoxin, there was no correlation between cytotoxin adsorption by tumor cell lines and their cytotoxin susceptibility, suggesting that resistance to the cytotoxin is expressed at a post-receptor stage. Preliminary studies on the cytotoxin receptor of K562 cells showed that it is probably not the transferrin receptor, and that protein but not carbohydrate is essential for its function.