Competitive inhibition of passive sensitization of mouse mast cells by IgE. A bioassay for mouse and rat IgE.

Possibility of inhibition of an efficient in vitro IgE-sensitization system was studied. The sentization of mouse peritoneal mast cells with an anti-ovalbumin IgE-rich fraction of serum, as tested by ovalbumin-induced degranulation, was inhibited by previous incubation with antisera of another or of no specificity. Fractionation and other experiments showed that the inhibiting activity correlated with IgE content. IgGl did not seem to have an effect. Sensitization was also inhibited by rat myeloma IgE, 50 ng giving a 50 per cent inhibition. Plots of the logarithms of rat and mouse IgE concentration vs their inhibitory effect on sensitization gave two parallel linear curves, indicating that mouse and rat IgE compete for the same receptor sites. It was thus possible to use this system as a sensitive bioassay for both mouse and rat IgE levels and, by comparing inhibition by mouse IgE to that by a known rat IgE standard, to obtain not only relative data but absolute mouse IgE levels. This, and also a better discrimination of IgE doses, was the major advantage of this bioassay in relation to the equally sensitive anti-IgE degranulation tests.