ABSTRACT
A human T hybridoma was generated lacking demonstrable low-affinity IgE surface receptors. This cell line produces spontaneously immunoglobulin-binding factors. The factors have an affinity for human IgE and IgG as well as for IgG from other species. The binding factors were purified by concanavalin A affinity chromatography, an IgE immunoaffinity column and SDS-PAGE. This purification procedure resulted in five major proteins bands at 13, 15, 30, 60 and less than 150 kilodaltons. As judged by Western blot analysis, all bands were variably glycosylated and were capable of binding IgE. Biological activity resided even within the small molecular weight (13 kilodaltons) peptide in terms of inhibiting IgE synthesis of the U266 B cell line and net IgE synthesis of B cells from atopic blood donors. Additionally, semipurified binding factor preparations also inhibited the Pokeweed mitogen-induced IgG synthesis while stimulating IgE synthesis at the same time. At present it is not clear whether the different molecular entities are dimers or polymers of the same protein, or are all derived from one larger protein (proteolytically cleaved), or whether they are completely different peptides mediating similar immunoglobulin-binding capacities as well as similar biological activities. Glycosylation of binding factors is not responsible for binding to immunoglobulins, but might be important for its biological activity.
