NATURAL RESISTANCE IN MICE AGAINST FRIEND CELLS INJECTED INTRAVENOUSLY III. COMPARISON BETWEEN IN-VIVO AND IN-VITRO PASSAGED INTERFERON-SENSITIVE 745 AND INTERFERON-RESISTANT 3C18 CELL CLONES

In vitro (FLC-Vt) or in vivo (FLC-V) passaged Friend erythroleukaemia cells of DBA/2 origin were tested for susceptibility to natural resistance (NR) in vivo or to NK cell activity in vitro. Scarcely oncogenic FLC-Vt cells were highly susceptible to in vivo NR (measured as rapid organ clearance or growth inhibition in lethally irradiated mice) or to in vitro NK attack. Conversely, highly oncogenic FLC-V cells were weakly susceptible to NR and to NK as well. These data seem to point out that natural immunity, which is up-regulated by endogenous or exogenous interferons, can play a significant role in surveillance against mouse leukaemic cells of retrovirus origin.