Elevated mutant frequencies in lymphoid tissues persist throughout plasmacytoma development in BALB/c.lambda LIZ mice

Using the phage lambda LIZ-based transgenic in vivo mutagenesis assay, the mean mutant frequencies in the target gene, lad, were found to be significa ntly increased in lymphoid tissues of congenic BALB/c.lambda LIZ N-5 mice i n the terminal stage of a plasmacytoma induction experiment, 213-280 days a fter the first i.p. injection of the plasmacytomagenic agent pristane (2,6, 10,14-tetramethylpentadecane). In plasmacytoma-bearing mice (n = 7), mutant frequencies in the spleens and mesenteric lymph nodes were elevated 2.46-f old and 5.35-fold, respectively, when compared with age-matched controls. I n plasmacytoma-negative mice (n = Il), mutant frequencies were increased 2. 30-fold (spleens) and 3.48-fold (mesenteric nodes). These results, interpre ted in conjunction with our previous findings (K, Felix et at, Cancer Res., 58: 1616-1619, 1998) of approximately 3-fold elevations in pristane-induce d splenic mutagenesis on day 42 postpristane, indicate that increased mutan t levels in lymphoid tissues persist throughout plasmacytomagenesis in gene tically susceptible BALB/c mice.