Analysis of the growth characteristics of a primary BALB/c IgG plasmacytoma

Spontaneously arising and chemically or virally induced tumors usually cannot be analyzed in the early stages of tumorigenesis. Growth characteristics of these tumors thus are not available and it is unkown whether their expansion at any stage is influenced by the immune system. We have developed the following strategy to evaluate possible deviations from exponential growth in initial stages when a tumor is not yet manifest and in order to overcome the two main objections against most experiments in tumor immunology: use of possibly selected transplantable tumors and high initial cell doses. BALB/c mice received 0.5 ml of Pristane intraperitoneally three times within 16 weeks. This treatment induces plasmacy‐tomas in 58% of the animals within I year. Mice were bled twice a week beginning with the 5th week after the last injection and sera were stored. Guinea‐pig anti‐idiotypic antibodies were raised against the IgG myeloma protein of a plasmacytoma developing in mouse 6‐15 and a radioimmunoassay was set up. Sera of mouse 6‐15 were then tested in retrospect for appearance and increase of the myeloma idiotype Id 6‐15. We followed this idiotype thus for 19 weeks from a concentration of about 10 μg/ml up to 3 mg/ml serum. Plasmacytoma 6‐15 cell growth was calculated from the Id 6‐15 levels. In early phases wave‐like fluctuations were found, possibly due to varying ratios of secretor to total plasmacytoma 6‐15 cells. This phase was followed by an exponential increase in secretor cell number. At no time was there evidence for anti‐idiotypic auto‐antibodies against Id 6‐15. The data are discussed in connection with possibly early activation of cellular components of the immune system.