Functional expression of the high affinity receptor for IgE (FcεRI) in human platelets and its intracellular expression in human megakaryocytes

The high affinity IgE receptor (Fc epsilon RI) expressed on the cell surface of mast cells and basophils is the key molecule in triggering the IgE-mediated allergic reaction. Recently, it was elucidated that the Fc epsilon RI is expressed on a variety of other cells like Langerhans cells, monocytes, and eosinophils, and the functional importance of the Fc epsilon RI expression in Langerhans cells was also shown. Some studies suggest that human platelets may play important roles in allergic inflammation through the cell-surface expression of the Fc epsilon RII and Fc gamma RII. Here, we report that human platelets and megakaryocytes constitutively express the messenger RNA and protein for the Fc epsilon RI. Although the Fc epsilon RI is expressed on the cell surface of human platelets, it is only detected in the cytoplasm of human megakaryocytes. We also confirmed that human platelets express the genes for the alpha, beta, and gamma chains of the Fc epsilon RI without any defined mutations. Furthermore, stimulation of human platelets via the Fc epsilon RI induced the release of serotonin and RANTES (Regulated on Activation, Normal T Expressed, and presumably Secreted). Taken together, these results suggest a novel and important role for human platelets in perpetuating allergic inflammation through the expression of and activation via the Fc epsilon RI. (C) 1999 by The American Society of Hematology.