T- and B-cell-derived supernatant factors enhance IgE synthesis by a myeloma cell line (U-266)

IgE synthesis by the human myeloma line U-266 was enhanced 3- to 15-fold in the presence of supernatants from cultures of mononuclear cells (MNC). The enhancing activity was concentration-dependent and was derived from cells that were cultured in the absence of serum and received no in vitro stimulation by exogenous mitogens or lymphokines. T- and B-lymphocyte-enriched populations isolated from MNC were found to generate the enhancing activity, but no enhancing activity was produced by monocytes. MNC from atopic and nonatopic donors were equally effective as sources for this activity. The enhancement of IgE synthesis was proportionally greater than the effect of the activity on cell proliferation. Furthermore, this enhancement of IgE synthesis was demonstrated to be isotype-specific in that the factor(s) had no effect on IgM- and IgG-secreting cell lines. It is suggested that augmentation of IgE synthesis by B cells at a late stage of differentiation may be accomplished by lymphokines constantly present in the cells' milieu and that the U-266 model may be useful for testing putative IgE regulatory factors.