Downregulation of high affinity IgE receptor FcεRI expression in the human basophilic KU812 cells by a tea catechin

High affinity IgE receptor FcepsilonRI express on the cell surface of mast cells and basophils, which is a key molecule in the allergic responses through IgE. Human basophilic KU812 cells express FcepsilonRI, in this study, we investigated the effect of major tea catechins, (+)-catechin (C), (-)-epicatechin (EC), (-)-epigallocatechin (EGC), (-)-epicatechin gallate (ECg), (-)-epigallocatechin gallate (EGCg) on the cell surface expression of FcepsilonRI in KU812 cells. FcepsilonRI is a tetramer consisting of alpha, beta and gamma chains. It is known that FcepsilonRI alpha extends into the extracellular space and contains the entire IgE-binding site. The cell surface expression of FcepsilonRI was measured by flow cytometric analysis using anti-FcepsilonRI alpha antibody. This analysis showed that the among tea catechins, EGCg only decreased the cell surface expression of FcepsilonRI for 24 hr treatment in serum-free condition. Moreover, the decrease of FcepsilonRI alpha protein level was observed by Western blot analysis. We measured the mRNA level of each subunit of FcepsilonRI in KU812 cells treated with EGCg by RT-PCR methods. The mRNA levels of FcepsilonRI alpha and gamma was decreased by the treatment with EGCg. Taken together, these results suggest that EGCg has an ability to down-regulate FcepsilonRI expression, and the down-regulation of FcepsilonRI may be due to the suppression of FcepsilonRI a and gamma mRNA levels.