The effect of α and γ-interferon on proliferation and production of IgE and β2-microglobulin in the human myeloma cell line U-266 and in an α-interferon resistant U-266 subline

An IFN-resistant subline (U-266^r_α) was established from the IFN-α-sensitive myeloma cell line U-266 by subculturing U-266 cells with increasing doses of INF-α. The U-266^r_α secreted IgE at a higher rate than the U-266 (7.2 × 10^?13 g/c/8 h as compared to 3.3 × 10^?13 g/c/8 h). The 2 cell lines were found to be equally high producers of β₂m (9.2 and 9.6 × 10^?13 g/c/8 h). The U-266 produced 2.9 times less IgE and 5 times more β₂m compared to the initial production rates at establishment. INF-α and recombinant IFN-αM₂ (rIFN-α₂) inhibited proliferation and concomitantly decreased the rate of IgE and β₂m secretion in U-266 but not in U-266 IFN^r_α, which in contrast was slightly stimulated by IFN-α with respect to growth, IgE and β₂m secretion. In addition, IFN-α at a concentration of 100 U/ml was shown to decrease the IgE and β₂m production without exerting more than minimal cytotoxicity on U-266 cells. No antiproliferative effect was found for IFN-γ or recombinant IFN-γ (rIFN-γ) on either of the 2 cell lines. IFN-γ and rIFN-γ were, however, found to stimulate the production of β₂m. Our results show that the U-266 and the derived IFN-α-resistant subline can be used as models for studying some of the biological effects of IFN-α and -γ in vitro. The clinical implications of these in vitro results, in particular the usefulness of serum determinations of immunoglobulin and β₂m concentrations for monitoring the tumor cell mass, are discussed.