Synthesis and regulation of the IgE receptor on B lymphocyte cell lines

The synthesis and ligand-dependent regulation of the lymphocyte receptor for IgE (Fc epsilon R) has been studied. Using murine Fc epsilon R+ cell lines, a 44-kilodalton 35S-methionine-labeled Fc epsilon R precursor was isolated by immunoaffinity chromatography. In contrast to the final processed 49-kilodalton Fc epsilon R, this precursor cannot be isolated from IgE affinity columns, indicating the importance of this processing in the function of the Fc epsilon R. The IgE-mediated Fc epsilon R upregulation was also studied and it was demonstrated that the degradation rate of the Fc epsilon R was dramatically slowed by ligand occupation of the Fc epsilon R. This degradation involves the cell surface-mediated release of a 38-kilodalton Fc epsilon R fragment that can be isolated using monoclonal anti-Fc epsilon R antibodies. Thus, these results demonstrate that posttranslational processing is required for the lymphocyte receptor to gain significant IgE-binding capacity; once acquired its degradation is slowed by occupation of the Fc epsilon R with ligand. At least in the rodent model system, this slowing of the degradation helps explain the increased Fc epsilon R levels seen in the presence of high IgE levels.