Searching for measles virus in Crohn's disease

Background: Intestinal epithelial cells (IEC) differentiate morphologically and functionally as they migrate from the crypt to the villus.Recent studies indicate that cellular differentiation alters the immunoregulatory potential of IEC.This study analysed the mechanisms of a differential proinflammatory cytokine response in undifferentiated vs differentiated HT-29 cells.Methods: Parental (HT-29/p) and Methotrexate-differentiated HT-29/ MTX10-3 cells (provided by Dr. T. Lesuffleur, INSERM u17g, France) were stimulated with IL-113, TNF-~ or PMA.Dose-dependent secretion of IL-g was assessed by ELISA, degradation of IKB~ by Westem blot analysis, activation of transcription factors by Jun kinase assay and EMSA, and IL-8 gene expression by Northern blot analysis.Transient cotransfection with an expression vector for IL-1RI and a reporter gene for the IL-8 promoter (gift from Immunex, Seattle and Dr. G. Wu, Philadelphia) was achieved by lipotransfection, and promoter activity was assessed by luciferase assaY.IL-1 receptor density was determined by radiobinding of t25I-IL-l[3.Results: Differentiated HT-29/MTX10-3 cells stimulated with IL-I[~ secreted 80% less IL-8 than HT-29/p cells, while no significant differences were found with induction by TNF-ct or PMA.IKB~ was not degraded in either cell line following IL-113 stimulation, but NF-KB binding activity was only increased 1.5fold in IL-113 stimulated HT-29/MTX10-3 compared to a 9fold increase in HT-29/p cells.NF-~:B activation was comparable when TNF-~t was used as a stimulus.Furthermore JNK activation and IL-g gene expression were greatly reduced in IL-113 stimulated HT-29/MTX10-3.Although HT-29/MTX10-3 cells contained increased intracellular IL-1 receptor antagonist (IL-1Ra) type I, receptor blockade by secreted extracellular IL-1Ra was not responsible for differences since pretreatment with anti-IL-1Ra did not increase IL-8 secretion.Transfection with an IL-1R expression vector restored the IL-113 stimulated IL-8 promoter activity in HT-29/MTX10-3 cells to the level found in HT-29/p, suggesting differences of IL-1R density and/or function between the two cell lines.However, binding of l~I-IL-1 [3 was comparable in both cell lines.Conclusion: Permanent cellular differentiation of HT-29 cells selectively impairs the IL-1 signaling pathway.This alteration may explain 1. the perpetuation of intestinal inflammation in conditions where high epithelial cell turnover leads to an increased number of undifferentiated cells and 2. indicate a potential mode of pharmacological action of Methotrexate in IBD.