Antiallergic Tea Catechin, (−)-Epigallocatechin-3-O-(3-O-methyl)-gallate, Suppresses FcεRI Expression in Human Basophilic KU812 Cells

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Abstract
We previously found that the O-methylated derivative of (−)-epigallocatechin-3-O-gallate (EGCg), (−)-epigallocatechin-3-O-(3-O-methyl)-gallate (EGCG‘ ‘3Me), has potent antiallergic activity. The high-affinity IgE receptor, FcεRI, is found at high levels on basophils and mast cells and plays a key role in a series of acute and chronic human allergic reactions. To understand the mechanism of action for the antiallergic EGCG‘ ‘3Me, the effect of EGCG‘ ‘3Me on the cell surface expression of FcεRI in human basophilic KU812 cells was examined. Flow cytometric analysis showed that EGCG‘ ‘3Me was able to decrease the cell surface expression of FcεRI. Moreover, immunoblot analysis revealed that total cellular expression of the FcεRI α chain decreased upon treatment with EGCG‘ ‘3Me. FcεRI is a tetrameric structure comprising one α chain, one β chain, and two γ chains. The level of mRNA production of each subunit in KU812 cells was investigated. EGCG‘ ‘3Me reduced FcεRI α and γ mRNA levels. The cross-linkage of FcεRI causes the activation of basophils, which leads to the secretion of inflammatory mediators including histamine. EGCG‘ ‘3Me treatment inhibited the FcεRI cross-linking-induced histamine release. These results suggested that EGCG‘ ‘3Me can negatively regulate basophil activation through the suppression of FcεRI expression. Keywords: Tea catechin; basophil; KU812; FcεRI; O-methylated EGCg