Synthesis and Regulation of the IgE Receptor on B Lymphocyte Cell Lines

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

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