An electron microscope study of receptor site on rat mast cells for human immunoglobulin E

Previous studies using immunofluorescence and autoradiography demonstrated the presence of specific immunoglobulin E (IgE) receptors on rat mast cells (RMC). This finding was confirmed by the use of transmission electron microscopy (TEM) combined with X-ray microanalysis (XMA) employing ferritin labelled antisera XMA was used to detect ferritin as Fe in the target cells. On examination by TEM and XMA, 25 per cent of RMC showed a dense area of Fe deposits on the surface of the cells. No Fe could be detected on neutrophils or eosinophils or in the control cell preparations without human IgE. The Fe was concentrated in well-defined areas of the treated mast cells and this distinct concentration of receptor sites was similar to that observed by other investigators who have termed this phenomenon, "cap" formation.