Resistance to Moloney murine sarcoma virus (M-MuSV) tumor induction is associated with natural antibody production to "endogenous" Moloney leukemia virus (M-MuLV) in BALB/Mo mice.

BALB/Mo mice are characterized by early expression of "endogenized" M-MuLV and are resistant to M-MuSV tumor induction. Furthermore, compared to normal BALB/c mice, sera from BALB/Mo mice exhibit a significant reactivity which is specific for M-MuLV when tested in a 125I-labelled Staphylococcus protein A binding assay. The possible significance of this reactivity in conferring tumor resistance is explored.