The binding of human myeloma IgE immunoglobulin on rat mast cells was studied by three independent techniques. A mixed agglutination reaction with anti-IgE-coated Sephadex granules demonstrated that only human IgE-coated rat mast cells were clearly agglutinated. This binding is strong (50 agglutination) in 3 min and progresses for 30 min (95 agglutination). Autoradiographic studies with 125I-labelled human serum proteins demonstrated the selective formation of grains on mast cells incubated with labelled IgE. Upon action of anti-IgE antiserum on IgE-coated rat mast cells, the mast cells released up to 47.5) of their total histamine content in a fluorometric histamine assay. A relationship was established between sensitizing doses of human IgE and histamine release. These results bring evidence for a binding of human IgE on rat mast cells and imply the existence of receptors for this immunoglobulin on mast cell membrane.
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