As reported previously, and confirmed here in 26 donors, the serum IgE level (2.6-5,500 ng/ml) correlates well (rs = 0.95, P < 0.001) with the in vivo number of IgE molecules/basophil (6,000-600,000). The total number of IgE receptors/basophil was monitored by incubating them with an IgE-rich serum (15 μg/ml), quantitatively stripping IgE from the cells at pH 3.7, and measuring eluted IgE by a direct radioimmunosorbent test. Saturation of receptors for each donor was achieved with 15 nM IgE (3 μg/ml). The proportion of receptors occupied in vivo correlated with the serum IgE (rs = 0.84, P < 0.001) whereas the average association constant of the receptors was independent of serum IgE and ranged from 7.1 x 108/M to 2.8 x 1010/M, averaging 7.7 x 109/M. Unexpectedly, the total number of IgE receptors/basophil was closely related to the serum IgE level (rs = 0.92, P < 0.001). Thus, either there is genetic association between serum IgE and the number of basophil IgE receptors, or, more likely, the receptor number is modulated by the serum IgE concentration.
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