Increased expression of the IgE Fc receptors on rat macrophages induced by elevated serum IgE levels.

Macrophages (M phi) from rats with elevated serum IgE levels induced by (i) Nippostrongylus brasiliensis (Nb) infection, (ii) IgE-secreting plasmacytoma IR 162, or (iii) i.p. injection of purified rat IgE, and M phi from normal animals cultured in the presence of 10 micrograms/ml IgE were analysed for Fc IgE receptors (Fc epsilon R) expression. To detect Fc epsilon R-bearing cells, a rosette assay employing fixed ox erythrocytes coated with rat IgE was used. With undersensitized indicator cells a significantly (P less than 0.002) greater number of M phi from animals having elevated serum IgE levels or of M phi cultured in the presence of IgE formed IgE rosettes than M phi from normal donors. The IgE rosettes were IgE class-specific, since they were inhibited by rat IgE in a dose-dependent manner, but not by any other rat Ig class, heat-denatured rat IgE or human IgE. The modulating effect of Fc epsilon R expression on M phi was IgE specific, because neither rat IgG nor heated rat IgE induced increased IgE rosette formation. Furthermore, elevated serum IgE levels did not increase the expression of Fc receptors for IgG subclasses. Studies of 125I-IgE binding showed that alveolar macrophages (AM phi) from Nb-infected rats bind IgE with similar affinity (Ka 1.1 X 10(7) M-1) as AM phi from normal animals, but they have increased numbers of IgE binding sites. Collectively, the results demonstrate that in vivo and in vitro elevated serum IgE concentrations induce increased IgE rosette formation as a result of a marked increase in the number of Fc epsilon R per macrophage.