The free form of the α-subunit of the high-affinity IgE receptor is rapidly degraded but stabilized by IgE

Several studies have demonstrated a positive correlation between the expression of the basophil IgE receptor, FcepsilonRI, and the level of IgE. We aimed at studying the mechanism employing a radioimmunoassay, which detected the soluble form of the receptor's alpha-subunit (s-alpha). Using the human basophil leukemic cell line KU812, it was demonstrated that extracts of lysed cells contained substantial amounts of s-alpha. The soluble form turned out to degrade in a time- and temperature-dependent manner but, interestingly, the presence of IgE reduced this degradation dramatically, suggesting that the liganz stabilizes the receptor. Complexes between IgE and its receptor can be found in serum, and their concentration is well correlated to the IgE level. Secondly, 51 patients suffering from birch and. grass pollinosis and 16 nonallergic subjects were tested, and s-alpha was detected in the serum of all subjects (range: 68-3975 pg/ml). The season (birch, grass, or outside both seasons) did not influence the s-alpha quantities, and. neither were these related to the involvement of target organ, i.e., rhinitis vs. rhinitis + asthma, but correlated (r = 0.51,p < 10-4) to serum levels of IgE. Circulating levels of the alpha-subunit of FcepsilonRI are most likely to be determined by constitutive turnover and total IgE serum levels, and not by inflammatory-induced release.