Immunoregulatory functions of paf-acether. VIII. Inhibition of IL-4-induced human IgE synthesis in vitro.

In the present study we showed that paf-acether (paf), a naturally occurring phospholipid cytokine, down-regulated IL-4-induced IgE production by mononuclear cells from healthy nonatopic donors in a dose-dependent fashion from 10 microM to 10 pM. Kinetic studies indicated that addition of paf together with IL-4 strongly decreased IgE synthesis from day 7 up to day 14. By contrast, paf had little or no inhibitory effect on the levels of IgM, total IgG, and IgA production. The inhibition of IgE synthesis by paf occurred independently of known inhibitors of IgE synthesis, IFN-gamma, PGE2, and transforming growth factor-beta because the addition of anti-IFN-gamma (10 micrograms/ml) mAb, indomethacin (0.1 microM), or anti-transforming growth factor-beta (10 micrograms/ml) mAb, together with paf and IL-4, did not overcome the inhibition of IgE synthesis. Finally, paf not only inhibited IL-4-induced IgE production but also reduced both germ-line and productive IgE transcripts levels by 77 and 67%, respectively, suggesting that modulation of IgE production by paf occurred at the transcriptional level. Taken together, these results suggest a novel IgE regulatory mechanism by phospholipid cytokine.