Interferon-α and the synthetic glucocorticoid dexamethasone are used in the treatment of multiple myeloma. The effect of 48 h exposure to recombinant interferon-α 2b (100 to 10,000 U/ml) and dexamethasone (1 μM to 1 mM) was studied in AF10, an IgE-secreting myeloma cell line. Interferon-α and dexamethasone at 10,000 U/ml and 1 mM respectiviely had a synergistic inhibitory effect on IgB concentration. Interferon-a and dexamethasone had an additive inhibitory effect on myeloma cell concentration. Interferon-α at 10,000 U/ml caused a twofold increase in sialyltransferase activity. Dexamethasone decreased sialyltransferase activity and attenuated the stimulatory effect of interferon-α. These data suggest that combined interferon-α and dexamethasone therapy might have a synergistic effect on monoclonal protein production and a diverse effect on sialyltransferase activity.

A STA was observed in a human-derived myeloma cell line, AF10, that produces IgE paraprotein. The STA in the culture medium of the AF10 myeloma cell line was associated in the 24 to 48 hr period of incubation with IgE biosynthesis, and increased thereafter up to 72 hr, while IgE remained stable. These data support our previous observations that human myeloma cells are associated with a relatively high production of sialyltransferase, which is released to the medium, presumably by a mechanism of shedding.