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Inhibition of the growth of murine tumour cells in vitro by serum from non-immune syngeneic and allogeneic mice.

Sera from DBA/2 and Quackenbush mice (which are non-immune for mastocytoma and Sarcoma 180 respectively) contain a heat-labile (56 degrees for 30 min) component(s) that inhibits the in vitro growth of DBA Mastocytoma P-815 X-2 and Sarcoma 180. Adsorption of the sera with tumour cells at 4 degrees did not eliminate the factor(s), suggesting that it is not an antibody. In liquid suspension cultures inhibitory activity was observed at concentrations of mouse serum of 10--20% and in semisolid agar clonogenic cell assays at concentrations as low as 1%. The influences of the inhibitor(s) for both tumours and in both culture systems were parallel. However, there was a quantitative difference in susceptibility to other environmental factors (FCS concentration, bicarbonate concentration, and O2 tension) between the two tumours. These results parallel the in vivo findings where intravenously injected mastocytoma cells produced more tumours than did Sarcoma 180.