Flagellin stimulation suppresses IL-7 secretion of intestinal epithelial cells.

IL-7 is a cytokine, which regulates development, maintenance and proliferation of T lymphocytes within the human immune system. Production of IL-7 is observed in a sterile environment such as thymus or bone marrow. However, it is also known that intestinal epithelial cells (IECs) residing in close contact with numerous bacterial stimuli also produce IL-7. Here we show that secretion of IL-7 by IECs is significantly suppressed upon stimulation by various bacterial components, including flagellin. Analysis of the intracellular mechanism by which flagellin regulates IL-7 production revealed that flagellin down-regulates expression of the two major transcripts encoding IL-7. Surprisingly, such function of flagellin was independent from the known transcriptional regulation of the IL-7 gene, as no significant change was observed in the transcriptional activity regulated by the previously identified promoter region. As the stability of IL-7 mRNA also remained unchanged upon flagellin stimulation, results suggested the possible involvement of a yet unknown transcriptional regulation of the IL-7 gene. These results describe a novel regulation of IL-7 production by bacterial stimuli, presumably mediated via Toll-like receptors. The present system might contribute to regulate the local lymphocyte pool, in response to the gut luminal or sub-mucosal bacterial abundance.