RARα agonist AM580 induces CD1d expression on LCL and inhibits LEF-1 binding to the CD1d promoter. (A) CD1d transcriptional levels measured by RT-PCR of LCL treated with (+) or without (−) AM580 for 72 hours. CD1d-transfected C1R (C1R-CD1d) and parental C1R cells shown as positive and negative controls for CD1d expression; RT-PCR loading control was cyclophilin A (CPA). (B) Representative surface CD1d (solid lines) and isotype control staining of LCL treated with AM580 for 0, 24, 48, and 72 hours. (C) MFI values (■) of CD1d indicate positive CD1d staining above the isotype control of LCL generated from unrelated individual tonsil samples (n = 10). **P < .01. (D) The specific binding of LEF-1 to the CD1d promoter in unrelated LCL (LCL 1-4) was measured by chromatin immunoprecipitation experiments performed in duplicate and is decreased compared with untreated LCL after incubation with AM580 (100 nM) for 96 hours. ***P < .001. Chromatin immunoprecipitation assays were repeated twice and completed independently at separate times, using LCL generated from 4 unrelated donors.