Tehran University of Medical Sciences Iranian Journal of Allergy, Asthma and Immunology 1735-1502 8 4 2009 12 15 177 183 Reza Safaralizadeh Department of Biochemistry, National Institute of Genetic Engineering and Biotechnology, Tehran, Ira Zahra-Soheila Soheili Department of Biochemistry, National Institute of Genetic Engineering and Biotechnology, Tehran, Ira Abdolkhaleg Deezagi Department of Biochemistry, National Institute of Genetic Engineering and Biotechnology, Tehran, Ira Zahra Pourpak Immunology, Asthma and Allergy Research Institute, Tehran University of Medical Sciences, Tehran, Ir Shahram Samiei Iranian Blood Transfusion Organization Research Center, Tehran, Iran Mostafa Moin Immunology, Asthma and Allergy Research Institute, Tehran University of Medical Sciences, Tehran, Ir 2015 10 01 FcεRI, The high affinity receptor for IgE plays a critical role in triggering the allergic reactions. It is responsible for inducing mast cell degranulation and deliberation of allergy mediators when it is aggregated by allergen and IgE complexes. FcεRI on the mast cells consists of three subunits; α chain directly binds IgE, β chain and dimmer of γ chains together mediate intracellular signaling. Cross-linking of IgE-bound FcεRI on the surface of mast cells and basophils by the multivalent antigen induces release of chemical mediators. The present in vitro study was designed to investigate the effect of synthetic FcεRI-α siRNA on the antigen-induced activation of MC/9 cells. MC/9 cells which are murine mast cells were transfected by FcεRI-α siRNA and negative control siRNA. After 6 h, anti-DNP (Dinitrophenyl) IgE was used for the cells sensitization. Then the cells were challenged with Dinitrophenyl-Human Serum Albumin (DNP-HSA) for mast cell degranulation induction before collection of supernatants. The amount of mRNA and protein expression was measured by Real Time PCR and western blot analysis, respectively. Determination of the expression rate of FcεRI-α on cell surface was achieved by flow cytometry. ELISA and spectrophotometry methods were used subsequently for measuring the effects of FcεRI-α siRNA on antigen-induced histamine and β-hexosaminidase release. FcεRI-α siRNA treated cells showed significant decrease in FcεRI-α mRNA and protein expression in comparison to control cells. FcεRI-mediated mast cell release of β-hexosaminidase and histamine were also inhibited. In this study it was shown that FcεRI-α siRNA could suppress FcεRI-α expression and inhibited degranulation and histamine release in antigen-stimulated MC/9 cells. In conclusion, knock-down of FcεRI-α by siRNA could be a promising method for inhibition of the mast cell-mediated allergic reactions. https://ijaai.tums.ac.ir/index.php/ijaai/article/view/254 https://ijaai.tums.ac.ir/index.php/ijaai/article/download/254/254