Interaction of high or low metastatic related tumor lines with normal or lymphokine-activated syngeneic peritoneal macrophages:in vitro analysis of tumor cell binding and cytostasis

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Abstract
Peritoneal macrophages from normal DBA/2 mice were found to bind significantly more cells of a syngeneic low metastatic lymphoma line (Eb) than cells of a high metastatic variant (ESb) derived therefrom. These differences were observed in three different assays, at 4°C and at 37°C, and at various ratios of macrophages to tumor cells. Upon co-culture with normal macrophages, a tumor cytostatic effect was consistently observed with Eb but not with ESb tumor cells. Further experiments indicated that macrophages exerted their growth inhibitory effect via direct tumor cell contact. Pre-treatment of tumor cells with neuraminidase or pre-treatment of macrophages with lens culinaris lectin increased the numbers of macrophages binding Eb and ESb tumor cells. Addition of D-galactose or D-mannose at 50 mM concentration led to an increase of tumor cell binding and tumor cytostatic activity. Taken together, these results suggest (i) that carbohydrates play a role in tumor cell recognition by macrophages and (ii) that the differences observed between Eb and ESb tumor cells may be due to differences in the expression of carbohydrates. Pre-activation of the macrophages by lymphokine(s) led to a short increase in their tumor cell binding capacity. Lymphokine activation resulted in a strong but also short-lived increase of tumor cytostatic potential. This was effective against both the low and the high metastatic tumor line.