Characterization of immunoglobulins eluted from murine tumor cells: Binding patterns of cytotoxic anti-tumor IgG

In this study we tested whether or not a correlation exists between the immunochemical character, the biological activity and the binding patterns of IgG prepared from low pH eluates of tumor cells harvested at various stages of tumor growth. The experiments were carried out using SEYF-a cells, a polyoma virus-induced ascites tumor, propagated in syngeneic A.BY mice. It was found that IgG eluted from tumor cells consisted mainly of IgG2a molecules. The specific cytotoxic activity of these IgG preparations was highest in eluates from 11-15-day-old tumor cells, and it decreased with propagation time of the tumor. This indicated the fixation onto old cells either of IgG2a molecules with no cytotoxic activity, or of molecules with the capacity to inhibit such an activity. Simultaneously the binding patterns of these IgG preparations also changed with propagation time of the tumors. IgG molecules eluted from SEYF-a cells 11-15 days after inoculation of the tumor were homogeneous with respect to their binding constant to the corresponding tumor cells. Thus, a correlation was indicated between the exclusive presence of antibodies with a high-binding constant and a high-specific cytotoxic activity. On the other hand, IgG molecules eluted from SEYF-a cells 26-30 or 38-42 days after inoculation of the tumor were heterogeneous with respect to their binding patterns to tumor cells. Such preparations contain IgG molecules with high-binding constants as well as those with low-binding constants. IgG preparations from serum or from ascitic fluid of tumor-bearing mice demonstrated at all stages of tumor propagation heterogeneity with respect to their binding pattern to the cells and low levels of cytotoxic activity compared with IgG from tumor eluates.