CYTOKINE-STIMULATED RELEASE OF DECAY-ACCELERATING FACTOR (DAF CD55) FROM HT-29 HUMAN INTESTINAL EPITHELIAL-CELLS

Expression of DAF (CD55) is enhanced on colonic epithelial cells of pa tients with ulcerative colitis (UC), and stool DAF concentrations are increased in patients with active disease. Cytokines are known to modu late DAF expression in various human cells, and lesions of UC reveal a ltered profiles of cytokine production. In this study, we evaluate the effects of various cytokines, IL-1 beta, IL-2, IL-4, IL-6, IL-8, IL-1 0, and interferon-gamma (IFN-gamma), on the synthesis and kinetics of DAF protein in HT-29 human intestinal epithelial cells. Using flow cyt ometry and an ELISA, we found that HT-29 cells constitutively express DAF on the cell surface and spontaneously release DAF into the culture supernatant under standard culture conditions. When the culture super natant was centrifuged at 100 000 g, nearly a half of DAF was precipit ated, indicating that one half of the released DAF was present as a me mbrane-bound form and the other half as a soluble form. Analysis of th e culture supernatant of biotin surface-labelled MT-29 cells suggested that the soluble form DAF was derived by secretion from within the ce ll or by cleavage from the cell surface. Among the cytokines, IL-4 mar kedly, and IL-1 beta moderately, enhanced the expression and the relea se of DAF. Actinomycin D, cycloheximide, and brefeldin A inhibited the increase in DAF release induced by IL-4 and IL-1 beta stimulation. Th ese results suggest that DAF is released from intestinal epithelial ce lls in response to cytokine stimulation and that IL-4 and IL-1 beta ar e possible cytokines involved in DAF release into the colonic lumen of patients with UC.