Modulation of cell-bound and soluble CD23, spontaneous and ongoing IgE synthesis of human peripheral blood mononuclear cells by soluble IL-4 receptors and the partial antagonistic IL-4 mutant protein IL-4 (Y124D).

We studied the influence of human recombinant soluble interleukin-4 receptors (sIL-4R) and a partial antagonistic mutant IL-4 protein, IL-4(Y124D), on the in vitro CD23 expression, soluble (s)CD23 release and IgE synthesis of human peripheral blood mononuclear cells (PBMC). The data show that sIL-4R suppressed the IL-4-induced IgE synthesis of PBMC. sIL-4R fusion protein stabilized with human Fc gamma fragments showed a more pronounced effect than unconjugated sIL-4R. IL-4(Y124D) also suppressed the IL-4-induced IgE synthesis. The IL-4-induced antigen CD23 and its soluble fragments were suppressed by sIL-4R and IL-4(Y124D). PBMC of atopic donors with a spontaneous in vitro IgE synthesis showed a partial suppression of the IgE production after sIL-4R or IL-4(Y124D) application. The IgE synthesis and sCD23 release of normal donor PBMC were suppressed when the substances were applied 0-4 days after IL-4 treatment. After 4 days of IL-4 stimulation, sIL-4R and IL-4(Y124D) enhanced the IgE synthesis. These data demonstrate that sIL-4R and IL-4(Y124D) are suppressive for the primary IgE synthesis induced by IL-4. In contrast, the ongoing IgE synthesis was only partially modulated by sIL-4R and IL-4(Y124D), and in some conditions even an enhancement of the IgE production was observed. These data suggest a differential function for IL-4 in the early and late phase of PBMC IgE production.