IgE Content and IgE Receptor Expression of Mast Cells in Normal and Nematode-Infected Rats

A cytofluorometric method was used to measure the native IgE content, the number of IgE receptors available for binding, and the degree of saturation of the receptors on microscopically identified mast cells. The peritoneal mast cells of normal, naive, murine pathogen-free Sprague-Dawley rats as well as of Wistar and Hooded-Lister rats raised under controlled conditions and without signs of infection, were found to carry a significant number of IgE molecules with unknown specificity. The IgE content varied greatly among the individual mast cells within a given population, but, on average, 60-70% of the receptors available for binding were occupied. During an infection with the nematode worm, Nippostrongylus brasiliensis which is associated with an elevated serum IgE level, an increased number of IgE receptors on the peritoneal mast cells was already found on days 2-3 of the infection, preceding a reduction of mast cell numbers and an inflammatory response in the peritoneal cavity. This up-regulation of IgE receptors occurred much earlier than a previously observed increase in serum IgE.