Inhibition of interleukin-4 production in activated T cells via the downregulation of AP-1/NF-AT activation by N-lauroyl-D-erythro-sphingosine and N-lauroyl-D-erythro-C₂₀-sphingosine

Allergic diseases are hypersensitivity disorders that are associated with the generation of specific immunoglobulin E (IgE) in response to environmental allergens. Interleukin (IL)-4, which is primarily produced by the CD4 ⁺ T cells, is an important stimulus for the switching of the antibody isotype to IgE in both mice and humans. In a previous study, we demonstrated that ceramide derivatives coupled with a lauroyl group exerted strong inhibitory effects on IL-4 production in T cells. In this study, we attempted to characterize the mechanisms underlying the inhibition of IL-4 production in T cells. Two ceramide derivatives, N-lauroyl-d-erythro-sphingosine and N-lauroyl-d-erythro-C₂₀-sphingosine (hereafter abbreviated as LES and LECS, respectively), were shown to significantly inhibit the production of IL-4 in both primary CD4⁺ T cells and EL4 T thymoma cells in a dose-dependent manner. LES and LECS also inhibited the activity of the IL-4 gene promoter in EL4 cells transiently transfected with IL-4 gene promoter constructs, but this effect was impaired in EL4 cells that had been transfected with an IL-4 promoter construct deleted of a P4 site harboring the AP-1 and NF-AT binding sites. Furthermore, LES and LECS inhibited the DNA binding activities of both AP-1 and NF-AT transcription factors. In addition, LES and LECS were demonstrated to suppress PMA-stimulated PKC activity, although they exerted no significant effects on the protein levels of the conventional PKCs. These results indicate that the ceramides, LES and LECS, may inhibit the production of IL-4 in the activated T cells, via the downregulation of AP-1/NF-AT activation and PKC activity.