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Abstract
BackgroundThe IgE-mediated activation of mast cells and basophils results in the secretion of many substances, including the release of FceRI-alpha subunit. This released alpha subunit can bind IgE and it may act as a down-regulator of subsequent IgE-dependent reactions. However, previous studies do not observe loss of the mass of FceRI-alpha associated with the cells, at least not for human basophils. This study was designed to understand the basis for the discordant observations.MethodsPurified human basophils were stimulated with multiple activating secretagogues and supernatants were examined for histamine and released FceRI-alpha. In addition, cell surface IgE densities (occupied and unoccupied) were measured by flow cytometry and total cellular content of mature and immature FceRI-alpha determined with Western blots.ResultsReleased FceRI-alpha, on average, represented 7% of the total surface FceRI before the reaction. The molecular weight of the soluble FceRI-alpha was approximately 54 kD, larger than immature subunit and somewhat smaller than surface subunit. In addition, 1) release ceased long before internalized FceRI-alpha was processed, 2) release was insensitive to Bafilomycin A, 3) release was independent of the starting density of FceRI and 4) release occurred more effectively with non-IgE-dependent stimuli, FMLP or C5a.ConclusionsThere appears to be relatively constant amount of nearly mature FceRI-alpha that is susceptible to secretion events induced by any form of stimulation. The amount, on average, represents about 7% of the mature form of FceRI-alpha.
Highlights
IgE-mediated activation of basophils and mast cells results in the secretion of substances, e.g., histamine, that generate the signs and symptoms of the allergic response
Purified human basophils were stimulated with multiple activating secretagogues and supernatants were examined for histamine and released FceRI-alpha
1) release ceased long before internalized FceRI-alpha was processed, 2) release was insensitive to Bafilomycin A, 3) release was independent of the starting density of FceRI and 4) release occurred more effectively with non-IgE-dependent stimuli, FMLP or C5a
Summary
IgE-mediated activation of basophils and mast cells results in the secretion of substances, e.g., histamine, that generate the signs and symptoms of the allergic response. Studies by Fiebiger and colleagues [1,2,3] have demonstrated the presence of the alpha subunit of the receptor in the serum of subjects and this group has shown the appearance of an alpha subunit in the supernatants of an in vitro-stimulated mast cell line. In both cases, this solution-phase alpha subunit is able to bind IgE and the investigators have proposed that it can act as a feedback inhibitor of further allergic reactions because it becomes a “sink” for binding IgE that prevents its ability to sensitize cells expressing the high affinity receptor. This study was designed to understand the basis for the discordant observations
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